454 runs great, then starts to missfire and surge

[Bachster]

I've started a new post on my 92 Fleetwood Flair because I now have a lot more info and better description of the problem.
92 P30 Chassis with 454 with the following parts replaced.
New Fuel Pump
Fuel Filter
Temperature Control Sending unit
Ignition Control Module
Dist cap and rotor recently replaced
O2 Sensor recently replaced
Plugs replaced
Tension leads recently replaced
Catalytic Converter removed.
The vehicle starts, idles, runs and pulls really well. This lasts from start up for about 10 minutes or so, then it starts to missfire, bog down and surge.
When its surging you can also see the fuel injector spray pulsing in time with the surging.
****This is the really important part*******
If I stop, shut it off, turn it right back on again whatever the issue was has reset itself and it runs perfect again for another 5 minutes or so then starts to missfire, surge etc again.
So whatever the issue is, it has to be electronic of some sort otherwise cycling the ignition wouldn't make a difference, that would mean fuel pressure as well since Cycling the key should not make a change in fuel pressure. Once it starts to crap out, it will stay that way, even in park and trying to rev it up with no load, it will pulse and missfire.
I've tried disconnecting the EGR Valve and plugging the vacum line, no change. I've unplugged the EGR solenoid, no change, same with unplugging the MAP, Throttle Position Sensor and Idle Control Valve.
If someone has experienced this before I'd sure like to hear what you did to resolve.
Thanks Randy

[Gary45]

in any fuel injection system the fuel pump is before the injectors and after the injectors is the the fuel pressure regulator. so, is the engine following fluctuating fuel pressure which you can see or the reverse. I would be inclined to think either fuel pump pressure is flutuating or pressure regulator is. Perhaps install a t fitting inline that you can connect a pressure guage to. Fuel pressure is ussually regulated to around 60 psi.

[1972VWbus]

92 P-30 chassis 454 fuel pressure is 9-13psi. Only the 94-95 years had 26-32psi. Have you confirmed the fuel pressure with a pressure test kit? Do not assume the pump you put in is good.


The ICM controls pulsing of the fuel injectors.


https://harristuning.com/Tbi/troubleshooting/


Timing should be 4 BTDC with the distributor connector disconnected.

[cadillac_al]

I would investigate how the injectors are fired in more detail. I don't understand how the ignition module could do it but it could be a way to save money. The troubleshooting link doesn't really address that part of the system. GM usually used a Hall effect switch in their HEI distributors to fire the fuel injectors in other vehicles. It does sound like the fuel injector firing is confused. It could be a simple defective fuel pump or regulator too. I have never owned a GM truck TBI vehicle but it is supposed to be very reliable.

[azpete]

i didnt see where you replaced the plug wires. i had a 95 itasca that had the same problem. i also went thru the same testing. i found that the plug wires were failing after running from 5 minutes to 1q/2 hour. when i replaced them with a hei racing plug wire set, from summit, the problem went away.
i also had to replace two ignition modules. weak spark signal.

[Soppy]

In the OBDI GM 454 TBI engines,the ECM uses a signal from the ignition module to determine engine RPM and the injector pulses. It sure sounds like the problem could be the ignition module. Install the original module and see if that solves the problem. You might need a program like Tuner Pro RT to read the "live data" from your engine. It will give you all the sensor readings , timing, injector pusle width , duty cycle , etc. I got the program off ebay about 7 yrs ago and run it on an old laptop.

[1972VWbus]

Also pull any engine codes from the ECM using a paperclip....

https://www.youtube.com/watch?v=i_Y7TiVqsBA

[1972VWbus]

The following are OBD-1 codes for it....

https://www.troublecodes.net/gm/#codesobd1

[Bachster]

So one of the biggest issues I've ever had with forums is you can read an entire thread and then it stops, no indication if the problem was ever solved and if so how and what was the cause. I promised myself I would not be that person so here goes, the problem is solved.
I was able to get a loaner fuel pressure tester from the jobber store. Tried to hook it up at the throttle body but the steel fuel line was not flexible enough to allow for the additional space required for the adapter. I was able to find a connector from the steel line to a flexible line back to the steel line just under the passenger side frame rail which allowed the movement of the engine separately from the chassis. Inserting the adapter there allowed the gauge line to be passed up through the dog house opening so it could be monitored while driving.
At start up it pressured up to 13 psi and held that steady under full throttle and long loads. After about 8 to 10 minutes it started to drop and the engine performance issues started to appear.
When it was at it worst conditions the fuel pressure was down to 8 or 9 PSI.
Shut it off and back on it was instantly back to 13 to 14 psi. Started to run it again and it was fine for about 3 or 4 minutes then the pressure started to drop and performance again fell apart.
So it was definately a fuel issue. Having already replaced the pump I was reluctant to accept that I could be so unlucky as to have gotten a bad fuel pump.
Pulled the tank again and removed the fuel sender/pump assembly to see if there was anything obvious and there was.
The fuel sock that attaches to the bottom of the pump looked like it was 50 years old. Removed it and you couldn't see any light getting through it so it was pretty obvious crap in the tank was the route cause. I think when I pulled the tank the first time I had drained the fuel to make it a bit easier to manage. The tank was empty for 4 or 5 days and I think that was just enough for the 30 years of scale etc to dry up. When I put it back in I cleaned it up best I could and then put fuel in it. I think that washed out the crap and the first time I fired it up after fueling it the sock probably loaded itself up with all that crap and probably reduced its capacity right away.
I think as it ran subsequently, the more the pump tried to draw the more crap started to plug up the few spots still available to draw fuel until it was restricted enough that it would loose pressure. As soon as it was shut off, no longer creating a suction enough of the crap would drop off that it would momentarily work as expected.
I replaced the sock, cleaned things up again and ran it with the pressure tester again. This time 13 to 14 psi, never dropped a bit, even on a very long steep hill starting from a dead stop.
I'm not overly optimistic that I'm in the clear of the crap in the tank, if I can get through a full tank of driving without issue then perhaps. I did buy a spare sock and at least I know I can get the tank out in about 30 minutes.
On the plus side, I think I've got a pretty bullet proof runner now that its had a full tuneup, new Ignition Control Module, Temperature Contol Sender and the Catalytic Converter removed.
Thanks to all who had responded and offered up suggestions, hopefully somebody else will find this helpful.
Randy

[ChrisDParise]

Great.news! Thank you for.closing the issue.