1994 brave 454 7.4 tbi Engine won't stay running with new coolant temp sensor

kellyerenee · April 20, 2022, 09:34 PM

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.

eXodus · April 21, 2022, 09:41 AM

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,,?

kellyerenee · April 21, 2022, 09:52 AM

Two wire sensor.

Eyez Open · April 21, 2022, 11:20 AM

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.

kellyerenee · April 21, 2022, 11:40 AM

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.

Eyez Open · April 21, 2022, 09:31 PM

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.

kellyerenee · April 21, 2022, 10:43 PM

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.

Eyez Open · April 21, 2022, 11:39 PM

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

kellyerenee · April 22, 2022, 10:52 AM

That is the part number we have for the cts we installed.

Mlw · April 22, 2022, 11:09 AM

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.

Eyez Open · April 22, 2022, 02:12 PM

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.

Mlw · April 22, 2022, 03:19 PM

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

kellyerenee · 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.

Eyez Open · April 22, 2022, 04:24 PM

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.

Eyez Open · April 22, 2022, 04:37 PM

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.

kellyerenee · April 22, 2022, 04:38 PM

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.

kellyerenee · April 22, 2022, 04:39 PM

We are trying to find someone with an obd1 scanner to help us but haven't found anyone yet.

Eyez Open · April 22, 2022, 07:49 PM

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?

kellyerenee · April 23, 2022, 09:56 AM

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.

Eyez Open · April 23, 2022, 02:05 PM

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

eXodus · April 23, 2022, 04:01 PM

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.

kellyerenee · April 24, 2022, 09:28 AM

Thanks for the information. We will work on getting this order. My son is very interested in this as well.

kellyerenee · 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.

Eyez Open · April 24, 2022, 12:12 PM

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?

kellyerenee · 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.