95 K2500 7.4L TBI issue

[MtnMan]

I need to know what fuel pressure is required for a 7.4L TBI. I don't get any codes, but it won't idle when cold and won't stay running long enough to warm up. I have replaced the fuel injectors, diaphram, ICV and ICU. I have 13PSI at the fuel line into the TBI. I have tried adjusting the throttle plates to no avail. Any ideas?

 

[PlayingWithTBI]

I have replaced the fuel injectors, diaphram, ICV and ICU. I have 13PSI at the fuel line into the TBI.

Which injectors? They should have a part number and/or color code on top of them. 94 - 95 7.4L used smaller injectors at 26 - 32 PSI (with a 28LB spring) fuel pressure. Earlier ones ran at ~13 PSI.

See chart below;

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[Schurkey]

As said--13 psi is nowhere near enough for a '95 7.4L with OEM injectors.

HOW is your vehicle so short on fuel pressure? Did someone put the wrong throttle body--with the wrong pressure regulator--onto that engine?

 

[MtnMan]

My service manual said 10-13psi and the truck has never had a problem until I had an injector go bad (started dripping at idle). It's a Ticonderoga engine. I bought new injectors from Rock Auto and installed them along with a kit diaphragm with the original spring (I also have an adjustable spring kit but did not use it). Maybe I bought the wrong injectors then. The new injectors may be for a higher pressure pump. I'll see if I still have the ones I took out and check part numbers. If anyone knows the stock part number I'd appreciate it.

 

[MtnMan]

As an addition I have a 93 Suburban with the same set up 7.4L and the only visible TBI difference is there is not a vacuum pot working the idle off the MAP sensor. It runs great.

 

[1997]

It's a Ticonderoga engine.

i assume mean tonawanda, that's was the BBlock plant for years.

how old is the 02 sensor?

 

[Schurkey]

My service manual said 10-13psi and the truck has never had a problem

Which service manual is that? Far as I know, "all' '94--'95 7.4L used the higher fuel pressure. But I haven't researched that in-depth.

That is a valid spec for V6 and small-block applications. Well, I think officially it's 9--13.

It's a Ticonderoga engine.

i assume mean tonawanda, that's was the BBlock plant for years.

Yes. Wanda was a really big girl.

Tonawanda was my guess, but maybe he means it was rebuilt or tuned by a company called Ticonderoga.

how old is the 02 sensor?

Reasonable question.

I'd also be suspicious of the throttle plates being misadjusted for minimum idle speed, with subsequent IAC issues. Or--IAC issues leading to misadjustment of the minimum idle speed. Those two are related.

As an addition I have a 93 Suburban with the same set up 7.4L and the only visible TBI difference is there is not a vacuum pot working the idle off the MAP sensor. It runs great.

I know some 7.4L had a vacuum-powered throttle-kicker. I don't know if they all did. Seems to me it was intended to help with cold idle. I only messed with one of them, and I was not very successful with it.

 

[454cid]

He's in Washington.... could possibly be a CA truck. Would a TBI era CA Emissions truck have different fuel pressure specs?

 

[MtnMan]

I contacted Chevrolet and those original injectors were discontinued based on my vin number. I got the original OEM number and am going to verify the replacements I got are compatible. I will be also looking up the specs for the idle settings at the throttle plates so I have a better starting point for IAC diagnosis. I appreciate all the leads here. I did download the TBI calibration pdf so once I get it to run I can set things up. I will also check the O2 sensor as it's original. Lotsa miles on the old truck. I may plumb in a higher pressure fuel pump just to see if that's the problem. Hang on for news.

 

[grampadirt]

Maybe I can help..My Burb is a '95 with a big block and sounds like it's the same setup as yours.This year big block needs fuel pressure to be 26-31 psi.The cold idle as Shurkey says is controlled by a diaphragm attached to the side of the tbi unit and that is controlled by the idle solenoid which is controlled by the pcm.There is a vacuum line going from the base of the tbi unit to that idle control solenoid and then on to the vacuum diaphragm on the side of the tbi.there should also be a wire connector attached to the the idle control solenoid so the pcm can turn it on and off.When the engine reaches a pre designated temp the pcm will activate that icm solenoid and cut the vacuum therefore releasing the idle vacuum diaphragm and dropping the idle to what the pcm wants.Hope I explained this correctly