We have a baffling problem with our rv. We replaced the coolant temp sensor near the thermostat housing. When we start the rv it won't stay running, we have to feather the gas pedal and it runs rough. So we tried unplugging the new one and plugged in the old one and set it on the housing. Started the rv and it ran perfectly no issues. It didn't even stall when we turned the air on or put it in drive. So we took the new cts out and replaced it with the old one Started the rv and it would not run again. So we unplugged the old one and plugged in the new outside of manifold and started it up and ran perfectly. Why does the sensor work outside of the manifold and not in the manifold?
We have even traced all the wires to the ecm. All complete there circuits. Please help wee have to have this running before June.
Probably to much dirt in the threads to make good contact.
Clean out the hole and use metallic cooper anti sieze and try again.
Is it a one or two wire Sensor,,?
Two wire sensor.
Your new CTS is not functional. One has to be very careful getting the right part for those TBI systems..stay with AC Delco if at all possible.
How Does an Engine Coolant Temperature Sensor Work?
https://resource-center.meineke.com/how-does-a-car-temperature-sensor-work/#:~:text=The%20tip%20of%20the%20CTS,the%20on%2Dboard%20control%20system.
Additionally, it may signal the need for a richer fuel mixture or open the exhaust gas recirculation.
So we unplugged the old one and plugged in the new outside of manifold and started it up and ran perfectly. Why does the sensor work outside of the manifold and not in the manifold?
When outside of the manifold the NEW CTS signaled the engine was cold which told the ECM to enrich the fuel mixture. It is also possible to work the other way...that would be enriching the fuel mixture when the engine was warm which is not good at all.
We did get ac Delco. Two of them as a matter of fact. Still runs the same with the ac Delco. It's just baffling that when it's in the intake manifold it doesn't work but when it's outside of the the intake manifold it works. We have changed out every electronically components on this motor and still the same results.
Is this engine cold when this happens? Does this engine clear up when warm? Do you have a pert number just for grins&giggles...it could be shorting out in some manner..something is changing the voltage when the sensor is In the engine.
With the cts in the manifold it's when cold, as it warms up it doesn't change it a bit and we have to keep feathering it to stay running. We turn it off swap out the cts and place it on the thermostat housing and restart it, runs perfectly. Can't read the part number on the original one we took out. Don't have the Delco number handy right now. That's what we are thinking is happening or a ground somewhere is bad not sure. Cleaned all the grounds from the batteries to the frame late this evening. Going to look for more tomorrow.
You may well have two sensors, one for the ecu and one for the gauge package each is different . Do not use Teflon tape as it can cause grounding problems. Just a quick net search gave the below AC part number. ACDelco Coolant Temperature Sensor 213-928
A link that may help you thru this, without knowing what the ECT is doing is going to be tough. Even a obd reader is only going to give you a bad ECT code..which you already know. Check the sensor wiring closely for fractures. Do the cooling fans turn on during this stumbling?
One oddity is feathering the pedal to keep it running, TBI should not respond that way. Maybe a fuel pressure check is in order here, parts stores generally have rentals... Your fuel rail should be at 30 psi..
https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-coolant-temp-sensor-1
That is the part number we have for the cts we installed.
As I read it you are making it much to difficult for yourself. It really sounds like a bad or wrong sensor to me. that it's new doesn't mean it can't be faulty.
The sensor isn't grounding when it's outside the engine, as there is no ground the sensor works as it gives high resistance to ground and then the engine runs well. The sensor does ground when it's placed in it's position, so ground resistance is low and the engine runs bad. 1+1=2
https://www.youtube.com/watch?v=puNKAW5Nurc
Measuring the sensor with a multimeter would be the best thing to do, then you are absolutely sure.
That ECT sensor is a two wire sensor, one hot one cold. Grounding to the block does not work,yet that appears to be what is happening.
But speaking to connectivity...is your ECT in contact with engine coolant? No contact no work...much like a thermostat. No coolant and it will not open...lol well maybe after things get to far along that is. A full cooling system would be quite critical...and no air pockets.
Just spit balling here.
I was indeed wondering about that because it was a two wire sensor. With my dodge it is a one way sensor, as in the most engines i came across during my years working for a yacht broker.
QuoteGrounding to the block does not work,yet that appears to be what is happening.
My point exactly. I also don't quite get why the sensor is replaced when this is the message?
QuoteSo we tried unplugging the new one and plugged in the old one and set it on the housing. Started the rv and it ran perfectly no issues. It didn't even stall when we turned the air on or put it in drive.
And just to be clear, not to put anybody down but help solve the problem and to prevent chasing shadows just because a wrong/faulty part:
https://www.youtube.com/watch?v=Qk8dkNv95XY&t=478s
We went through changing plugs, cap, rotor,wires tps sensor, iac control, map sensor, or sensor, ignition coil, ignition module, hoses, thermostat, vapor canister valve, exhaust gas recirculation vacuum solenoid, egr valve and the coolant temp sensor mounted in the intake manifold. This was all done due to this rv sat for a year without being started and we didn't want any issues when we go on a trip. Basically it was preventive maintenance. The original cts was replaced with ac Delco part number 213-928, which we thought was faulty. We tested thus by leaving the Delco one in the manifold unplugged. We got the original one and just plugged it in and set it on top off the engine thermostat housing to see what would happen. The rv started up with no hesitation. So we took the Delco one back and got a replacement thinking it was bad. Put the new replacement in the intake manifold plugged in and it would not stay running no matter what we did. The cts has two wires one yellow and one black. So with the second new Delco replacement in the manifold we unplugged it again and plugged the original one back in placed on engine thermostat housing, rv started up ran fine. So we pulled the Delco one out of the housing and put the original back in. Plugged it in started the rv and would not stay running with the original one in just like the new Delco one. We traced all the electronics to the ecm to make sure the circuits where communicating with each other. It is strange how the rv can run great with the cts mounted outside the manifold. Mind you which ever one is in the manifold it is left there when we unplug it and plug in the other one to set on the engine to test.
It has been 15 yrs since I've tinkered with efi but a another spitball here.
Two wire sensors are a isolated circuit, now if one of those wires connecting the ECT to the are broken then there is no circuit. A bit deeper if the power wire is active and the ground broken then placing the ECT in the engine block would ground the system and with bad results.
Checking the wiring from the efi loom to the ECT would be in order. Making sure the ground wire is not broken..that wiring is very old and while the outer skin might look good the inner core wiring may well have broken/fractured. When you plug in the ECT might create enough tension to break the signal...
Having two ECT bad in a row? Nope. Wrong ECT well maybe...shorting out twice in a row being plugged into the block...It happened.
Quote from: kellyerenee on April 22, 2022, 04:14 PM
We went through changing plugs, cap, rotor,wires tps sensor, iac control, map sensor, or sensor, ignition coil, ignition module, hoses, thermostat, vapor canister valve, exhaust gas recirculation vacuum solenoid, egr valve and the coolant temp sensor mounted in the intake manifold. This was all done due to this rv sat for a year without being started and we didn't want any issues when we go on a trip. Basically it was preventive maintenance. The original cts was replaced with ac Delco part number 213-928, which we thought was faulty. We tested thus by leaving the Delco one in the manifold unplugged. We got the original one and just plugged it in and set it on top off the engine thermostat housing to see what would happen. The rv started up with no hesitation. So we took the Delco one back and got a replacement thinking it was bad. Put the new replacement in the intake manifold plugged in and it would not stay running no matter what we did. The cts has two wires one yellow and one black. So with the second new Delco replacement in the manifold we unplugged it again and plugged the original one back in placed on engine thermostat housing, rv started up ran fine. So we pulled the Delco one out of the housing and put the original back in. Plugged it in started the rv and would not stay running with the original one in just like the new Delco one. We traced all the electronics to the ecm to make sure the circuits where communicating with each other. It is strange how the rv can run great with the cts mounted outside the manifold. Mind you which ever one is in the manifold it is left there when we unplug it and plug in the other one to set on the engine to test.
Well now that is quite a accomplished list, speaking for myself only it's time for a scanner to look at each and every point of the system. Aside from checking the wiring loom for breaks and doubling checking grounds I at a loss. But a system scanner would point out any or all bad readings.
We checked the yellow wire and black wire back to the ecm which it made a complete circuit. We tested the black wire to ground on the frame or on a bolt on the tbi and stil completed the circuit as grounded.
We are trying to find someone with an obd1 scanner to help us but haven't found anyone yet.
I've been thru a very difficult situation once with a old 454. Made short I had a 81 block in a 83 model yr RV..only a 81 model yr starter would work correctly in my RV.
Now on to yours. You have a 94, GM used a 30lb fuel pressure rail on only 1994 and 1995, all other yrs used 13psi on the fuel pressure rail. Meaning this two yrs have very different injectors, using the wrong ones would be brain death...to take it further I am quite sure new ones are no longer available..
I think it might be wise to get your VIN code go to a GM dealership and check into what type of TBI system you actually have. I took the casting number off my engine to determine what yr it was made in.
Now if that sounds crazy remember it's been a very long time since 1994, hundreds of data bases have been crossed over and updated..A seamless transition are words that should make any cringe.
Did you by chance change the TBI injectors?
No we just sent them to fuel injector connection in Cummings, GA for service. Which after they tested them they were working correctly and they only cleaned them. They sent them back to us a long with new orings and throttle body gaskets.
Ok well you do work on your own engines and you have efi so I will post a tool for you and a demo link. If your skill set can manage tunerpro it is quite a tool. Kids today just eat this stuff up and do quite well with it. You do need a laptop
TunerPro RT (free), ALDL OBD1 cable (~$60)
http://aldlcable.com/products/aldlobd1u.asp
https://www.tunerpro.net/downloadApp.htm
https://youtu.be/LscbiTcx34s
computer controlled engines are so much easier for a young person to understand W%
But everyone can learn it.
No idea if the OBD1 already carries the sensor data from the coolant sensor. Could be a something simple on/off threshold.
But my old electrician mindset is telling me - you have a grounding issue somewhere.
A two wire sensor should be isolated - so it there should be no difference if you run it outside or inside the manifold.
Do you have it dangling in the air when it's running? try to hold it against the engine block while it's running and see if it stutters or shuts down.
Maybe both sensors are shot, the old one from age and the new one from a bad design no improved. Get a known working one. But like other said - could be also the wiring.
They are selling pigtails - the last part of the wire from the plug to the harness - the one which gets hot.
Thanks for the information. We will work on getting this order. My son is very interested in this as well.
We have the sensor sit on top of the engine. We also have grounded it with a wire to the throttle body as it sits on the engine as well. It runs perfectly that way, but when we plug it back in to the one on the manifold it runs badly. We are on our fourth sensor and still get the same results.
Quote from: kellyerenee on April 24, 2022, 09:34 AM
We have the sensor sit on top of the engine. We also have grounded it with a wire to the throttle body as it sits on the engine as well. It runs perfectly that way, but when we plug it back in to the one on the manifold it runs badly. We are on our fourth sensor and still get the same results.
Wait here...Your running a new ground to the throttle body?
Are you saying you have the sensor plugged in and then you take a new wire and ground this new wire to the throttle body and the engine runs?
If so have you bolted in the sensor and grounded the system with this new wire? Did the engine run correctly then?
We have the sensor set on top of the engine next to the thermostat housing with the pigtail plugged in to that one and we run another ground wire to the block and the rv starts and runs perfectly. We have the other sensor screwed into the manifold with nothing plugged to it. It's just plugging the hole so we didn't loss the antifreeze.
Quote from: kellyerenee on April 24, 2022, 12:55 PM
We have the sensor set on top of the engine next to the thermostat housing with the pigtail plugged in to that one and we run another ground wire to the block and the rv starts and runs perfectly. We have the other sensor screwed into the manifold with nothing plugged to it. It's just plugging the hole so we didn't loss the antifreeze.
Ok there's the problem your grounding is bad. Unhook the battery and clean every contact with CRC cleaner...use it like a water hose. Every contact every connection the looms the battery the grounding straps.
The ECT is a self contained/ isolated circut... when you grounded the housing to the throttle body with a NEW/SEPARATE wire you introduced a new circut...actually you restored or grounded the entire system togethe. When you did your parts change over more than likely a ground hanging on the ragged edge was broken. It happens all the time. 1st video keeps it simple, your system uses a 5volt signal bad grounds cause chaos.
https://youtu.be/Ibuvo4Zz4rw
https://youtu.be/iuCIC1HjHVA :)clap
https://www.chevytalk.org/fusionbb/showtopic.php?tid/320934/
https://youtu.be/zr7q3m49Vpk
QuoteWe went through changing plugs, cap, rotor,wires tps sensor, iac control, map sensor, or sensor, ignition coil, ignition module, hoses, thermostat, vapor canister valve, exhaust gas recirculation vacuum solenoid, egr valve and the coolant temp sensor mounted in the intake manifold. This was all done due to this rv sat for a year without being started and we didn't want any issues when we go on a trip.
Well, I certainly can respect the fact that you don't want troubles on your trip.
Word of advise: Keep the old parts around in the RV as you know that they work. When something does go wrong you at least have spare parts.
Replace the braided ground strap from the engine block to frame. That is very likely your issue. Be sure both ends are clean...clean...clean. 'to just clean the one currently on the RV is bad idea. It's likely bad given it's age. Replace it entirely. Same with the battery ground cable. Once everything is tightened down coat with di-electric grease.
Sorry I haven't replied in a while. Thanks everyone for all the advice on our situation. We looked at all the advice we got and did everything you suggested with the exception of the cable and computer software. We are still having the same issue. We will keep trying until we find it. It makes no sense that the cts works outside the manifold and the one pulled into the manifold does work. We even switched each part we replaced one at a time to see it it just wasn't communicating with the sensor and got the same results. We checked all the grounds and they all are good and clean. If there's another ground that we are not aware of please let us know. Thanks
Check your injectors, the part numbers are on top. There is a good reasoning for this.
Rochester 17104288 that number is original. There is so much disinformation on 94/95 injectors it's stunning.
You said you hooked up a separate ground wire and it ran correctly, am I correct? If so simply make that new ground strap permanent. Plug in your ECT and if it runs correctly...well you need to take a deeper look into your grounding.
https://m.motormanfuelinjection.com/Rochester_TBI/fuel-injector-17104288.html
Ok here's what we tried today. We searched everywhere for the wiring schematic and find one close for our engine. We decided to trace the wires once again from the pigtail to the red and blue connectors. The tps and cts black wire tie together. The map and egr black tie together. With the ecm not connected each of these have no ground to the chassis. So we reconnected the ecm and tested the black wires. They have current on the black wires. We still have the same issue nit running with the cts pigtail plugged into the cts in the manifold. We checked all are grounds to the chassis and frame they are good. If someone has a link or website for the wiring schematic please let me know.
That might work
https://67-72chevytrucks.com/vboard/attachment.php?attachmentid=1311220&d=1412990365
That's one of the ones we are using.
That's one of the ones we are using.
Just one thing. Do you have two factory ground straps on or near the thermostat housing? The strap on the thermostat housing is it shiny squeaky clean?
When you added the extra wire and the engine cleaned up says it all. Actually if I were in your shoes that wire would be permanent...Code readers are 30 dollars perhaps that may assist you. There are times the code reader cannot read the ecu..This maybe one of those times.
Timeline 4:30. https://youtu.be/cjzHbyWfe_4
Yes we have that ground wire on the thermostat housing. Here's other thing we discovered we tested ecm prongs for the tps/cts and the egr/map where the black wires go into. The tps/cts are on the third prong red and the map/egr are on the fourth prong red. With our meter the pins three and four have conductivity which we think its just going into a loop circuit.
During startup these old engines run open loop, aka oxygen sensors not up and running yet. Timing fuel curves are set in stone. Not to much can happen when the system is cold..Actually I suspicion that grounding out the CTS defaults the ecu into open loop, that takes almost every sensor out of the loop aside from the Map...and the knock sensor...So how's your knock sensor up and running right? And you MAP is Ok?
We don't have a knock sensor. Map is good replaced with new one. It has Banks Header System on it.
Well know this is gretting interesting...94 actually I do not know of a 90's era 454 without a knock sensor. So have you looked or are you assuming. Plz do not take offense I know your skilled simply by following down the wiring. Banks would not eliminate a knock sensor...That would be rich. Are you the original owner? If not how long have you owned this RV
https://www.rockauto.com/en/catalog/chevrolet,1994,p30,7.4l+v8,1059634,exhaust+&+emission,knock+/+detonation+sensor,5108
Have you measured the CTS pins against it's housing/engine block ? Just regular resistance?
Should be infinite high. If you got any reading - the sensor is bad. New sensors come sometimes bad too. There should be no difference between screwed in and laying on the side.
Try the same for the pigtail end.
The knock sensor is somewhere down on the block and has 1 wire. I think mine was passenger side.
My guess is - as soon as you screw it in - you partially ground the positive from the ECU or you don't get a signal from the return line.
Those are tiny amps - I mean like 20mA, if there is a tiny inperfect in the sensor or wiring - it will not work
Yes we located the knock sensor and that's one we have not replaced. We are the third owners of this rv. Original own bought this and had the banks power system put on. He traveled all over the country in it. He actually lives down the street from us. The second owners only drive it barley 5,000 miles and then it sat for a year. He said something happened with the a/c had it checked. They a/c wouldn't come on so I'm not sure what they did to it. So he just parked it and didn't do anything else with it. When we got it we added freon and it worked but again not sure what they had done. They also worked on the fuel pump and not sure what they did there either.
Yes we have checked the voltage on the senso outside the block plugged in and we have low voltage. We are going to do some other testing and see what we come up with.
That all makes sense, might I ask did this RV idle well when cold and choppy when warm prior to the temp sensor change? Have you driven this RV much? Just a thought running that engine without a knock sensor can be very bad. TBI can and will cause detonation when running lean the knock sensors retard timing making the RV very sluggish.
As odd as this may sound,checking your fuel pump pressue would be the very first step. Only 1994/1995 tbi systems ran 26/30 psi pressures. All other yrs ran 11/13, that difference is huge actually the engine would struggle and eventually burn up.
Next are the injectors,94/95 are very unique. They are specially calibrated to handle the 30psi, they are no longer made. Taking it a bit further you cannot rebuild a tub injector, clean yes and install new screens. But once the spindle in them gets sloppy there done.I posted a link to oem refurbished injectors, notice the flow matched statement, meaning there cleaned and checked for proper flow rates.
The above is very old information in the marine industry, since 2007 actually. GM dumped high pressure systems to to epa issues, and the marine industry used the tech for their use. No epa regs on the marine industry back then
Don't assume anything on someone else's work, it will only cause headaches. Google the below statement and you will see some of the confusion.
94 95 454 fuel pump problems forums
Parts lookup by VIN. https://parts-catalog.acdelco.com/acesCat.php?
I posted this link due to the fact it is entirely possible to have a 94 model yr RV sitting on a 93 chassis/engine. This happens in a RV, cars no but RVS it happens.
Below is why I keep on over fuel pressure and the correct injectors, TBI will try to fix the supply problem and overwhelm itself.
https://www.gmtruckclub.com/threads/94-454-manual-runs-fine-in-open-loop-not-in-closed-loop.1475461/
ok.....
so it turns out it was bad fuel pump .... the 'new' one was no good
put the old one in and works fine.... so far
Model yr...1994 Hm?
1. Because the RV mfg had to order the chassis a year in advance, it was normal for the current model RV (94) to be mounted on a previous model year (93) chassis. Check your P30 VIN code to verify chassis model year. 10th digit is most likely a "P" indicating 1993. "R" is 1994. Make sure your ordering parts for the correct year chassis.
2. I did not see anywhere in this thread the OBD1 codes you currently have. This is an OBD 1 system so the engine codes can be read by shorting ALD pins "A" and "B" together (engine off) then turning the engine on (do not start) then counting the engine light flashes. In order to get more detailed info requires either a GM Tech 1 scan tool or using TunerPro RT (Post 19 (https://www.classicwinnebagos.com/forum/index.php?topic=16458.msg100819#msg100819)). Not even sure your troubleshooting the correct problem. CTS problem is either OBD Code 14 or 15. OBD1 ALD connector should be under the dash close to the steering wheel.
3. CTS is 2 wire unit like shown in post 10 (https://www.classicwinnebagos.com/forum/index.php?topic=16458.msg100803#msg100803). It is not grounded via the sensor case. CTS and TPS grounds are shorted together and grounded via the PCM. OBD sensors are connected like this because of the lower voltages used by computerized OBD systems.
4. Yes this engine does have a knock sensor. It is located on right side of engine just forward of the starter. With a 454 and 4L80-E tranny, it interfaces directly with the PCM. Other Chevy setups of this age typically had the knock sensor connected to the electronic Spark Control module.
5. Not sure if this will help or not however here (http://dave78chieftain.com/ChevyP30/1992_454_with_4L80-E_ECM_1of5.jpg) is the CTS wiring diagram for a 1992 P30 454 Chassis with 4L80-E trans.
6. When engine is cold the sensor resistance is high so the PCU sees a high voltage (~ 5 VDC). As the engine heats up the sensor resistance becomes less so at operating temp (85 - 95C) the PCU sees 1.5 to 2.0 VDC.
At 212F sensor resistance = ~ 177 ohms
At 140F sensor resistance = ~ 667 ohms
At 104F sensor resistance = ~ 1459 ohms
At 77F sensor resistance = ~ 2796 ohms
7. This works when not installed in the sensor hole issue sorta implies the cable is under stress and the 2 leads are shorting together when installed. Either that OR you have a idiot light sensor instead of a variable resistance thermo sensor. If you have a water idiot light on the dash then be advised there are 2 water temp sensors on that engine. One for PCU CTS and one for idiot light.
Any of the OEM TBI injectors for 94 still available?
VIN#1GBJP37N4R3314754
As always call them and verify,just for your peace of mind and warranty of course. The below website has long posted the correct injectors for yrs, very good reputation. I am not affiliated with them in any manner shape or form
https://m.motormanfuelinjection.com/Rochester_TBI/fuel-injector-17104288.html
https://m.motormanfuelinjection.com/Rochester_TBI.html
DavidVA78Chiefton do you have blue e and f connector, red a and b connector. I have attached the tag that's on the inside drivers side wall. Do you happen to have the complete wiring diagram for that 7.4 tbi. We can't seem to find it anywhere. We have blue 32 pin and red 32 pin connector. The plate on the inside drivers side panel say; Incomplete Vehicle by General Motors Corp 11/93 Month and year of Manufacture 11/93. Vin number 1GBKP37N9R3308453
Udidwht we had our injectors done by Injector Connection in Georgia.
Eyez Open the injectors are the original injectors the we sent to Injector Connection and they tested them. They were good. No the rv didn't run well before we changed the coolant temp sensor. We thought that was the problem, but it didn't fix it. We haven't driven it much because it won't run properly. When we put it in drive it dies, when we put it in reverse it dies. When we started testing the cts we only was able to drive for a short time before service engine light came on.
Your VIN 10th digit is "R" = 1994 chassis.
I just have the 1992 Chevy P30 Service Manual set however you can get used manuals on EBAY
1994 Chevy P service manual (https://www.ebay.com/sch/i.html?_odkw=1993+Chevy+P+Service+manual&_sop=15&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.X1994+Chevy+P+Service+manual.TRS1&_nkw=1994+Chevy+P+Service+manual&_sacat=0)
1994 is a 2 volume set.
I have always found the BISHKO PDF CD manuals to be complete (Service, Electrical, Driveability (OBD info), etc) and reasonably priced:
1994 Chevy P Chassis Motorhome Truck Shop Service Repair Manual CD Guide OEM (https://www.ebay.com/itm/150931998359?fits=Year%3A1994%7CMake%3AChevrolet&hash=item23243f8697:g:6tUAAOSwUuFWu9hM)
They are just scanned copies of the service manuals in PDF format. BISHKO site says this does contain chassis wiring diagrams.
Please note that P30 manuals only contain P30 chassis information. Wiring info for the rest of the RV has to be obtained from Winnebago (https://www.winnebago.com/Files/Files/Winnebago/Resources/Diagram/Wiring.htm)
While the manuals indicate wire colors, circuit numbers & wire size, they do not indicate PCM connector colors.
Dave
DaveVA78Chueftain thanks for the information.
TBI SENSOR DIAGNOSTIC - HOW TO WITH A MULTIMETER:
https://www.gmt400.com/threads/tbi-sensor-diagnostic-how-to-with-a-multimeter.18225/