I was traveling to the coast in my 95 suburban. It started acting up like it was running out of fuel, but if I can move the throttle or even get on it some and you can make it kick in and start pulling again. The engines acts like it is not getting fuel or when you get water in the fuel. I have an over bored tbi unit with a Prom I programmed and it has run pretty well. Needs some light tweaking, but overall runs decent. I have a vafpr to control some low rpm idle issues. Running venom fuel injectors. I have checked the fuel pressure and when the truck is acting up the fuel pressure is still there and goes up as the truck tries to stall and loses manifold vacuum. So I am thinking the fuel pump is not he issue. Could be in the injectors or somewhere else. Ignition? I need some ideas so I can get home in a couple of days. Just what I wanted to do on vacation fix the truck. YEAH! Can a bad o2 sensor make it run like that. I have had an exhaust leak near the o2 sensor before I tightened it back up. Could that kill the o2 or damage it.
Thanks for any ideas, I don't want to take it to anybody if I can help it, most mechanics don't want to work on vehicles that have been modified and they can't just throw parts at it.
Charles

 

i want to throw parts at it... fuel filter?

 

Replaced fuel filter last week (new purolator). It started erractically then got progressively worse. didn't think I would get the last 15 miles. One foot on brake one on gas to keep it running. On my datalog the TPS seems to be measuring correctly, MAP seems good. Cross counts are a little low. Seems to be running rich then spikes lean. The truck actually seems to be bogging when rich. Plenty of fuel in the tank...

 

I would place the FP gauge on windshield with duct tape and see what happens to FP under load. May require a passanger to monitor.

Did you try a datalog? See what sensors say during event.

 

Stuck IAC ?
Could clean it out and see if things improve.

 

The IAC is fairly new less than 5000 miles. The fuel gauge while driving is a problem since I am no where near home. I just ordered some AN fittings and another fuel gauge to monitor incoming fuel pressure not the regulated pressure, but haven't gotten it installed yet.

 

If you hold open the throttle it will run? Can you tell if it smells rich?

Coolant Temp Sensors can fail and make the ECM think it's -100F or whatever outside, and massively overfuel the engine to compensate for what it thinks is cold weather. But it will run if you hold the throttle open. Not sure if it's because it's resetting the TPS in regard to how open the throttle is or it's diluting the excessive fuel with air - either way, it causes something that seems similar to what you're describing.

See if you can tell if it's running rich.

When I had my TBI 305 in the car, my CTS plug managed to disintegrate, and every once in a while it would come undone and do something like that. And I'd have to go plug it in delicately and try to get both terminals to connect.

But to be clear, when it happened to me, I'd have to keep it at like 3k+ RPMs just to make it run in neutral. I cant imagine I would have been able to actually get anywhere. The car just wouldn't stay running. Your problem may be as obvious as it sounds with poor fuel delivery. But it's one of those things you may want to look into.

 

This isn't really PROM related, I'm going to move it to general tech/engine.

Since you said you had it running well enough to drive, then all of a sudden it wasn't running well anymore, I would say that it's a mechanical failure of some sort. Don't try and tune around a mechanical issue, it will only make it worse.

 

Sorry about posting in the wrong sub forum.

If CTS is the problem would the computer go to closed loop? The truck does go into closed loop with out a problem, but it does seem to be running real rich. Especially near idle speeds. the truck acts like it is cutting out, then you give it the gas a little more or you can step on it and it will kick in and pick back up.

 

vacuum line to the map sensor good? i had a small leak one with my old engine and it ran like that. it was compensating for the "low" vacuum and enriching the system. took me hours to figure that out.

 

Alright here is the latest. Went by a mechanics at the beach. The truck ran fine. Drew off a fuel sample and it looked fine, ran some Sea Foam thru it and it ran fine all the way home 4 1/2 hrs. Ran fine for a while then acted up one day a week or so ago. Ran fine for a while and I have a remote fuel pressure gauge at the side mirror. Today when my wife drove it in the rain it was acting up. One time she shut it off and restarted and it was better. Then it got worse in the rain then better as it dried out. I suspect a short at this point. Any sugestions on where to start?
Thanks, Charles

 

May be moisture getting to the ignition system.

 

I had considered this, but why would moving the accelerator pedal make the truck kick back in? I checked the TPS plug and it looks good but who knows. I have not been able to get a good datalog when it is really acting up. You know it won't do it when you want it to.
Charles