1990 454 tbi Help
 

Somewhat new to the website, I have 1990 Chevy v3500 454 Tbi. My problem begin a couple months ago. Been thru a bunch of old threads but cant figure this one out. Here's how it went down....

1. Truck started hesitating and missing under throttle. Idles fine.
2. replaced Egr valve
3. ran fine for a few weeks, then it started doing the same thing.
4. replaced Map sensor
5. ran good for about a month then....see #1 & #3
6. Today I did the old paperclip trick on the OBD connection. It read code 12.
Drove it down to O'Reilly's today with it running like crap. They plugged
into and it showed no codes either
7. Now I am starting to pull out what little hair I have left.

It has dual tanks, it runs the same on either tank, so I would think that would rule out fuel pump issues. I just don't understand why I would replace something then run good for a few weeks then back to the same ole same ole.
Your help is much appreciated!

Re: 1990 454 tbi Help
 

One thing I would check is the TPS voltage. Make sure it's nice and steady through the full gas pedal travel.

I would move to a wide band tester next to monitor a/f ratio to see if fuel is falling off or jumping up at the time of the stumble.

Re: 1990 454 tbi Help
 

Thanks, I will check it out and get back with ya'll

Re: 1990 454 tbi Help
 

Re: 1990 454 tbi Help
 

How old is the fuel filter. I had an old truck and the fuel filter plugged. I ran through the same things as you to find out the filter was crap. Changed it and everything worked fine after that.

Re: 1990 454 tbi Help
 

90 percent of the time when owners report missing under throttle, runs fine at idle indicates low fuel pressure. TBI system fuel pressure spec is between 9 to 13 PSI at the inlet to the TB. Get a fuel pressure gauge and TBI adapter and measure fuel pressure. I've seen TBI to run with 6PSI, but very poorly. The 454 drinks a lot of fuel when when it moves a heavy truck, while at idle only internal friction, and external loads need to be overcomed to keep engine idling. Measure FP first before tossing anymore new parts at it.

Fuel pumps usually are not a problem (but they do wear-out fast), but the fuel hose that connects outlet port to a fuel feed through turns soft and leaks after 23 years of service. Today's gas formulations contain ethanol (E10) which is unfriendly to older rubber compounds. If you end up replacing FPump and hoses make sure to replace the hose with SAE30R10 rated hose - Gates or Good Year make fuel submersible fuel hose.

//RF

Re: 1990 454 tbi Help
 

Thanks so much for your help guys, all this is new to me. Been working on and racing dirt bikes most of my life (old age shut that down) and just plain don't know anything about these things. I have figure out how to check the TPS voltage and checking the fuel pressure. Just bought a Chiltons online repair manual to help me locate these things. Going to the auto parts store again here in a bit to get a filter and a fuel pressure guage.

Re: 1990 454 tbi Help
 

Fuel filter.
Fuel pump psi validation.
O2 sensor functioning correctly?
Temp sensors functioning correctly?
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Re: 1990 454 tbi Help
 

Not to dis this site at all, but the best site for your truck is the 454SS website - they've been working with your identical system for years, should have all the answers.