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

[Eyez Open]

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     

https://www.chevytalk.org/fusionbb/showtopic.php?tid/320934/


https://youtu.be/zr7q3m49Vpk

[Mlw]

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.

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.

[udidwht]

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.

[kellyerenee]

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

[Eyez Open]

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

[kellyerenee]

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.

[Eyez Open]

That might work

https://67-72chevytrucks.com/vboard/attachment.php?attachmentid=1311220&d=1412990365

[kellyerenee]

That's one of the ones we are using.

[kellyerenee]

That's one of the ones we are using.

[Eyez Open]

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

[kellyerenee]

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.

[Eyez Open]

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?

[kellyerenee]

We don't have a knock sensor. Map is good replaced with new one. It has Banks Header System on it.

[Eyez Open]

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

[eXodus]

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

[kellyerenee]

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.

[Eyez Open]

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?

[DaveVA78Chieftain]

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).  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.  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 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.

[udidwht]

Any of the OEM TBI injectors for 94 still available?

VIN#1GBJP37N4R3314754

[Eyez Open]

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

[kellyerenee]

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.

[DaveVA78Chieftain]

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

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
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

While the manuals indicate wire colors, circuit numbers & wire size, they do not indicate PCM connector colors.

Dave

[kellyerenee]

DaveVA78Chueftain thanks for the information.

[Eyez Open]

TBI SENSOR DIAGNOSTIC - HOW TO WITH A MULTIMETER:

https://www.gmt400.com/threads/tbi-sensor-diagnostic-how-to-with-a-multimeter.18225/