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Old 09-13-2019, 03:12 PM   #1
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454 TBI wonít start when engine hot

I hope someone out there knows the answer I am baffled. Please read carefully this is complicated.

So... as stated I have a 1994 454 7.4 TBI (throttle body) on the Chevy P30 chassis that when the engine is warmed up - I get NO FUEL from either of the two injectors. UNLESS itís already running. This morning I started it let it run for over an hour got all the way up to temp so hot the aux fan kicked on gauge read 230f on dash and a steady stream of fuel from both injectors - no problems. Until I shut it off. Now it wonít start again. It did the same thing yesterday if I wait till tomorrow when itís cold and start it back up once again it will run fine indefinitely until I shut it off. I am baffled. Hereís what I have done so far..

Dropped the fuel tank and replaced the fuel pump. New fuel filter. New fuel pump relay. Tested oil pressure switch am not sure if itís good or bad not sure if itís normal open or close but incidentally again the engine will run fine indefinitely even at operating temp as long as itís already running. So I am assuming Iím good there. I also just strait up jumped the fuel pump relay tried to start and no dice. I am confident itís not the delivery system. And good oil pressure. Iím reading 40-50 psi on dash. I replaced the ignition module inside the distributer the cap rotor wires and plugs and the coil. Ran new grounds. I have tested the TPS sensor it reads 0 volts at idle 5 volts at full throttle AND tried to start it hot with tps unplugged (trying to eliminate ECM flood condition). If I pour fuel or either in the TBI it will fire a few times but no matter what if the engine block is hot the injectors donít open. Unless of course itís already running and it will run perfectly fine until I shut it off.

Has anyone seen this before ? Please pretty please ?

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Old 09-13-2019, 03:29 PM   #2
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230 degrees is overheating.

Have you tried restarting after an hour or 2 when it cools down.

Seems like its going into self protect mode.

Disconnect the water temp sensor and see if it restarts.
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Old 09-13-2019, 03:54 PM   #3
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Hi ! Welcome to IRV2! We're sure glad you joined the gang!

Wish I could help but I'm not a mechanic. Noticed you are kinda new on IRV2 and wanted to say hello!

Good luck, happy trails, and God bless!
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Old 09-13-2019, 04:46 PM   #4
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Update :

Ok I ran to town and bought a NOID set. I am absolutely not getting injector pulse on either injector. At least when the engine thinks itís hot. Which it should have cooled by NOW itís been like 6 hours I am baffled.

As far as 230f that was a guesstimate Iím going off a gauge on dash not an infrared and according to the wiring diagram the only thing that can interrupt the fuel supply is the oil pressure switch which I totally bypassed and ruled that out.

Back to being baffled .


And thanks Happy Camper ! Iím glad to be here. Iíve been lurking for a while I just donít post much.
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Old 09-13-2019, 04:58 PM   #5
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I am not familiar with the 454 in particular, but as an auto tech for 45 years I have seen this happen:

Engine coolant temperature sensor fails at extreme temperatures. As long as the engine is running, the ECU will provide a default value (Limp home mode) that will allow the engine to run. When attempting a restart, the ECU will NOT provide that default value, and a no start can occur.

Probably worth replacing the CTS as a test. They should be cheap and available.

A quick test would be to remove the CTS, cool it in ice water, and try starting. If it is a one wire connector, the case of the CTS has to be grounded. If two wire, that shouldn't be necessary.
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Old 09-13-2019, 05:42 PM   #6
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I would also check the connection at the ecu. Possibly bad connection when it gets hot.
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Old 09-13-2019, 05:46 PM   #7
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If the tbi sensors check out ok (throttle position sensor, coolant temp, egr etc), take a look at the distributor. There is probably an ignition trigger sensor. Electronics do not like heat. If you have higher mileage, might want to replace the distributor.
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Old 09-13-2019, 06:00 PM   #8
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usually the problem you are describing comes from a bad ignition control module, which you said you have replaced. IIRC the purple wire ( I think it is in the 4 terminal plug)is the pulse signal to the ecm for the fuel injection. Check that for signal. If you haven't already done so carefully check the wiring harness and plugs between the icm , ecm and injectors for continuity. If you haven't done so , reset the ECM by disconnecting the battery ground cable for a minute or two.
A lot of fuel issues are related to the ECM's temp sensor (located on or near the thermostat housing) When they fail they usually cause a flooding condition, I haven't heard of one shutting down the injector pulse, but if you are swapping parts looking for the cure this one is only about $20 the part number is 15326386
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Old 09-13-2019, 06:14 PM   #9
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The fuel pump wiring doesn't pulse the injectors. That the ECU job.
Quote:
Originally Posted by Thisguy0818 View Post
Ok I ran to town and bought a NOID set. I am absolutely not getting injector pulse on either injector. At least when the engine thinks itís hot. Which it should have cooled by NOW itís been like 6 hours I am baffled.

As far as 230f that was a guesstimate Iím going off a gauge on dash not an infrared and according to the wiring diagram the only thing that can interrupt the fuel supply is the oil pressure switch which I totally bypassed and ruled that out.

Back to being baffled .


And thanks Happy Camper ! Iím glad to be here. Iíve been lurking for a while I just donít post much.
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Old 09-13-2019, 06:23 PM   #10
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I would check to see if fuel is dripping into motor after engine shut down, that would cause hard start problems a few minutes after shut down, very common on gas motors that sit for long periods of time .
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Old 09-13-2019, 06:55 PM   #11
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Quote:
Originally Posted by bluepill View Post
I am not familiar with the 454 in particular, but as an auto tech for 45 years I have seen this happen:

Engine coolant temperature sensor fails at extreme temperatures. As long as the engine is running, the ECU will provide a default value (Limp home mode) that will allow the engine to run. When attempting a restart, the ECU will NOT provide that default value, and a no start can occur.

Probably worth replacing the CTS as a test. They should be cheap and available.

A quick test would be to remove the CTS, cool it in ice water, and try starting. If it is a one wire connector, the case of the CTS has to be grounded. If two wire, that shouldn't be necessary.
I should have added this too there are actually 3 temp sensors in this engine. One on each head over the manifold and one on the thermostat housing. Replaced all three earlier in the year chasing down a different issue where it backfires and misses on deceleration like going down hill or letting off gas. To that end I also had a massive exhaust leak at the down pipes and had to replace the gaskets (doughnuts) which I believe to have finally solved the exhaust leak and hopefully the other issue haven’t driven it since though BUT it’s interesting you point out the temp sensor because the third one the one on the engine front on the thermostat housing is replaced since I started seeing this new problem. I still have the old one. I could slave it in and make the computer think my engine is any temp I want with hot and cold water. Excellent idea !
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Old 09-13-2019, 07:01 PM   #12
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Quote:
Originally Posted by tomgrigsby View Post
If the tbi sensors check out ok (throttle position sensor, coolant temp, egr etc), take a look at the distributor. There is probably an ignition trigger sensor. Electronics do not like heat. If you have higher mileage, might want to replace the distributor.
I bought a brand new distributer today havenít installed it yet but itís the only thing left lol. I was thinking same as you even though I have replaced the cap rotor and ignition module inside it already the pip sensor I have not. So maybe just maybe that could be it. And the new one is complete unit all that included I can drop it in.
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Old 09-13-2019, 07:20 PM   #13
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Old 09-14-2019, 09:17 AM   #14
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Update: RESOLVED !!!!

Ok all. Excellent help here thanks ! In the end I wound up replacing the ENTIRE distributer and it resolved my issues. So even though I had replaced the cap rotor wires coil ignition module etc etc - what ended up being the culprit is the PIP sensor or points or what ever they are inside the actual distributer itself. By dropping a new complete distributer in I appear to have resolved the problem. It also seems to be running much better than it used to although I may have to fine tune the timing now. I will find out once I get it on the road and climb some hills and put it under load. Wish me luck - I am off to Florida (leaving upstate NY). Thanks for everyoneís help here and if anyone finds this thread later - replace your distributer. The whole thing.
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