454 TBI doesn't like operating temperature!!!

[Mike Harrington]

1989 454 TBI that starts and idles like a dream. Has a snappy throttle response and excellent power.....until it hits operating temp of 195. Now it will still sit and idle and I can put it in second gear and creep around all day with do problems. But once I give it the gas and it's above 190 it will hesitate, buck and if I'm quick enough and push the clutch in and take my foot off the gas it will just hiccup and die....I can then start it right back up. But if I'm not quick enough it will hesitate, buck, hiccup, and then backfire thru the exhaust and then die. But it will start right back up and idle all day long.
Here's the things I've done....the engine is slightly above stock with a comp cam 212/218 computer controlled cam. I also have a throttle body spacer. I recently changed the fuel pump and it's putting out 27 psi at the throttle body. The distributor is brand new with all new internals. The coil is original but checks out. 8.5mm wires with ceramic ends, new plugs. No vacuum leaks anywhere. Checked tb unit for play in shaft...it's tight. Fuel injectors give a very nice even cone pattern. Timing is set right at spec with wire disconnected. No codes are being thrown. Have double checked ALL sensors and connectors and all check out fine.
This truck originally came with the hot fuel module located behind the dash next to computer but the little voltage regulator on the circuit board resoldered itself....with two different modules so I just unplugged it. I don't know if this is the cause or not as their is very little info on that module as they only came on certain heavy duty trucks.
Also...the truck still has the original prom chip in it( I have a new one in the mail headed my way that has been returned for the new cam) so could that be the problem as well?
It's just strange that it only does it once it's warmed up. Any help appreciated.

 

[Bextreme04]

I'm by no means a TBI pro.... just a few thoughts though. I'm pretty sure it will be closed loop until warm, so the fact it starts running bad when it gets warm could be related to that. Have you checked the O2 sensor?

 

[Mike Harrington]

ALL sensors and their connectors have been double checked. It's a brand new 3 wire heated O2 sensor and no codes are being thrown

 

[RecklessWOT]

I had a similar situation with my 350TBI a few years back. I checked everything I could imagine, deleted stuff, replaced every electronic component. Ended up being a bad ECU.

The truck would start and idle perfectly normal, I could drive it around cold no problem, but when it was warm sometimes it would randomly cut out under load. Not every time, there was no way I could for sure tell when it was going to happen. Sometimes accelerating up a hill, taking off from a stop (especially if i had been idling for a bit before taking back off, taking lefts at busy intersections was a gamble), sometimes it would cut out for a second and backfire, other times it would straight up shut off. Had to drive around with a very deliberate and light throttle and still no grarantee.

Buddy at work brought in a computer he had laying around from when he swapped out his 305 (I figured close enough for troubleshooting), I went out and threw it in in the parking lot. Fixed everything good as new, truck ran like a champ for years after that.

 

[Mike Harrington]

I had a similar situation with my 350TBI a few years back. I checked everything I could imagine, deleted stuff, replaced every electronic component. Ended up being a bad ECU.

That's interesting....I have an extra ECU but it's from a 350 TBI with an auto transmission....my truck is a 454 with manual transmission. Would it work if I just put my prom chip in it?

The truck would start and idle perfectly normal, I could drive it around cold no problem, but when it was warm sometimes it would randomly cut out under load. Not every time, there was no way I could for sure tell when it was going to happen. Sometimes accelerating up a hill, taking off from a stop (especially if i had been idling for a bit before taking back off, taking lefts at busy intersections was a gamble), sometimes it would cut out for a second and backfire, other times it would straight up shut off. Had to drive around with a very deliberate and light throttle and still no grarantee.

Buddy at work brought in a computer he had laying around from when he swapped out his 305 (I figured close enough for troubleshooting), I went out and threw it in in the parking lot. Fixed everything good as new, truck ran like a champ for years after that.

 

[Mike Harrington]

Well I switched computers but no change. So I pulled the dizzy and went thru it.... again only this time I pulled the ignition coil of the dizzy and noticed there was no thermal paste under it!!! So I found some and lathered it up and re-installed everything and fired it up....waited for it to get up to temp and took it for a spin. Looks like I figured it out as it drove and ran like a champ. I guess the coil was working just fine until it got up to operating temperature and then got too hot and was cutting the signal out. Gonna run it into town later and see how it goes. Thanks to those who offered their ideas.

 

[JoeR Jr]

You need to get a scanner on it to see the readings. Anything else is shooting in the dark. There are a bunch of possible troubles that can be quickly confirmed or eliminated with one.
Joe

 

[Mike Harrington]

You need to get a scanner on it to see the readings. Anything else is shooting in the dark. There are a bunch of possible troubles that can be quickly confirmed or eliminated with one.
Joe

It seems to be running correctly now, besides I don't want to really go changing to much until I get the tuned chip for it. I should get that Thursday and then I will go from there.

 

[wanderinthru]

Well I switched computers but no change. So I pulled the dizzy and went thru it.... again only this time I pulled the ignition coil of the dizzy and noticed there was no thermal paste under it!!! So I found some and lathered it up and re-installed everything and fired it up....waited for it to get up to temp and took it for a spin. Looks like I figured it out as it drove and ran like a champ. I guess the coil was working just fine until it got up to operating temperature and then got too hot and was cutting the signal out. Gonna run it into town later and see how it goes. Thanks to those who offered their ideas.

Pulled the coil, or the module?

 

[Mike Harrington]

Pulled the coil, or the module?

My bad...the ignition module had no thermal grease under it

 

[wanderinthru]

My bad...the ignition module had no thermal grease under it

Thanks, I'm fighting an 89 that likes to go through modules, so just hunting information.

 

[Mike Harrington]

Yeah that thermal paste or compound is a straight up requirement. And dialectic grease is not a substitute.... although it's better than nothing. Back many years ago when I was learning about how to build computers we would use toothpaste as a substitute for thermal paste....in a pinch. I wouldn't recommend that for this application either....but once again it would be better than nothing!!!

 

[Camatruder]

Thanks, I'm fighting an 89 that likes to go through modules, so just hunting information.

Worn spark plugs or bad wires can destroy ignition modules.

 

[wanderinthru]

Worn spark plugs or bad wires can destroy ignition modules.

Well I be. Know the cap and rotor are visually good as are wires, Will replace the plugs, though I know I did when I bought it....???? But, that has been several years ago. This thing will run like a dream, never miss, never loose power, but once it's hot and you kill it, has to cool down for a half hour or so to start again?? Change the module and all is well. Changing the coil does not change anything.

 

[Swearbody]

Does the 89tbi use electronic spark control? I ask because that sounds like the problem i had recently with esc. Once the engine got to temp it would have similar problems. It was pulling time due to faulty esc controller or possibly the knock sensor, never found out just deleted it.
It may not even use it but what I found suggest that it does have esc. If none of the other suggestions work its worth a look at esc.