Once you have reached closed loop status and before you start having problems, how does the truck accelerate at WOT?

I am just trying to get a handle on what is really going on here.

I've come almost full circle based on this latest information thinking that it may be fuel supply related, but that wouldn't explain the zero V output from the O2s as even extremely lean, the output should still be around .1V...

Engine load dependent is what it sounds like which could still point to a bad PCM... Have you had any luck finding a replacement PCM on the cheap?

*EDIT* - Well, I just did some ebay searching and found a few PCMs that will work, however I did forget about the passlock programming that will be in these PCMs. It isn't as simple as just swapping it in, but for $90+s&h, it should work nicely. Just verify that your PCM is the same PN and they should be able to program to your VIN for you.

 

It accelerates fine when in closed loop and before the problems start. Also accelerate good when cold and in open loop just after starting up in the morning. Even going uphill on a short drive. No luck on the PCM except some on Ebay. Kept my eyes on O2 signals and trims from the start this morning. Check my grounds to the PCM and O2s this weekend and they were good. Thinking I'm going to pull the O2 right before the cat and drive it home tonight that way after work.
Thing is they (O2s) after the loading problem starts go back to switching their full range when I pulled over and sat there at idle. Floored the gas really fast and I can watch them drop and fuel trims jump up. Engine's rpms pretty much don't get past 2000. Engine stumbles alot like not getting enough gas. Pretty much the same symtoms I had when I had a bad fuel pump. That was replaced.
Had replaced the pump twice within a 2 year period. Funny thing about all this is I didn't have this problem until I replaced the fuel pump last time along with the fuel pressure regulator. About a week after the pump was replaced I started having this problem. I would check my fuel pressure but my pressure gage lost that center pin in the connector along with the O ring. Need to but another one. How cheap these thing are made. Still can't see the pump being the problem as I don't think it would affect O2s on uphill load conditions when engine is warm.

Thing is with the cat I read others here having very similar problems and it turned out to be there cat. Even though they didn't monitor their O2s and trims to see what was happening.

Brian

 

Does it depend on the fuel level? You could definitely rule out a fuel supply issue by driving around with the fuel pressure gauge on there, strapped someplace where you could watch it while driving.

I drove my old Intrepid around for a week without a hood and the fuel pressure gauge zip-tied to the windsheild wiper because I was having fuel issues with that. Ended up being a corroded wire under the car, but I only found that out after I had replaced the pump which helped, but it still stumbled at WOT. Ran a new wire from the relay all the way back and all of the problems went away.

 

I am having alot of Fuel gage problems been pegging over to full alot and drops down slowly as I keep driving. Can't trust the thing as I never know really how much fuel I have in the tank. Sometimes it reads high 3/4then low 1/4and back to high. Don't know if it is the sending unit or the ground to it. I had to splice on a different connecter on my wiring harness to the new pumpbecause of some kind of change GM did. I soldered the wires for a good connection and used heat shrink tubing on them and electrical tape to cover the connections. I'd really hate to drop that tank again. Took me 3 days to put in that pump. Had a real hard time getting the Filler hose lined up and another next to it again. Abouta whole daytrying to put the tank back in place.

You think if the engine wasn't getting enough fuel on heavy loads going up hill for instance that O2s might drop in output and trims shoot up? Possibility pump is heating up and failing to provide enough fuel? Wish it would just heat up a real lotin the tank and blow this truck up so I could buy another one. Also, if during this Load problem when I pull over if I slowly give it gas the Rpms will cover over 2000 to 3000 or more. Only if I punch it down will it stumble and hang around 2000.

Brian

Edited: Wow!

Lunch break, went out to the car and started it up cold, put it in drive and floored it ( trying to burn some rubber). Computer in open loop, Car stumbled, O2s went way down and trims shot up. Drove it to the gas station put more gas in it. Got back to work and in the parking lot floored it again, same thing, O2s down, trims shoot up, lots of hesitation and loss of power. This is just barely hot doing this. Car running maybe 15 minutes total.
Before I use to just floor it in idle with no load and it wouldn't do anything like this. It does this even cold and in open loop as well as closed loop and slightly warm.

Pump maybe?

 

It is possible that the spliced connection is at fault as well... A heated wire will reduce the voltage available to the pump, reducing its ability to keep up with demand, possibly lowering the fuel pressure which would create a lean condition that the PCM cannot compensate for. This makes more sense with the conditions you are having. I just have never seen O2 voltages that low, that means that there is practically equal O2 levels outside as compared with inside.

Can you get to the fuel pump connector without completely dropping the tank? I know I couldn't with my big hands & forearms... LOL!

If you can, you might want to redo the connections that you made... I was going to suggest loading the circuit, but you are talking a 300Watt draw to get to 25AMP current. A resistor to put that kind of load on the system would cost a bunch and get quite hot!

 

Lunch break, went out to the car and started it up cold, put it in drive and floored it ( trying to burn some rubber). Computer in open loop, Car stumbled, O2s went way down and trims shot up. Drove it to the gas station put more gas in it. Got back to work and in the parking lot floored it again, same thing, O2s down, trims shoot up, lots of hesitation and loss of power. This is just barely hot doing this. Car running maybe 15 minutes total.
Before I use to just floor it in idle with no load and it wouldn't do anything like this. It does this even cold and in open loop as well as closed loop and slightly warm.

Pump problem (wiring?) maybe?

I can get to the wires if I drop my spare and stick my head up there. I made sure I had extra length wires when I spliced them on so I can pull them out if I needed to get to them.


Brian

 

That is probably the second or third thing I would try. Pull the connection and redo the wiring. Maybe try some 3M butt connectors first and see if that helps. If it doesn't, then it is likely that the pump is the cause. I have used 3M butt connectors on several fuel pump wiring repair jobs and they have always worked. You should be able to find the required sizes at Walmart of all places! LOL

The first thing would be to actually monitor the fuel pressure. That will be a definitive finger pointing at the true problem. If the pressure waivers, then it is a toss up between replacing the filter or redoing the wiring connections that were made.

 

Filter is new replace that when I put the pump in. Tank was pretty clean inside. Old filter was really plugged, that must have killed the old pump. I stuck my hand up there (under my car over the tank) (not any where else) and looks like my electrical tape is completely falling apart. I can't see much as I have no light and my spare is still in the way. I'll have to get to all that tonight after I try and make my way home again[&o]. Still ******* police cars as my inspection is way expired because of all these problems (Sensor faults). Corrected now but can't get the car to complete it emmissions self tests it needs to make.
Hope it's just electrical connections really hate to have to drop that tank again put in another crappy OEM pump.
Brian

Added: Just thought of another way to check the pump. I could pull the fuse to it and drop an ampmeter across where the fuse goes. It would complete the circuit and monitor the current from the pump. If it changes then there would be a problem. Instead of taping a fuel pressure gage to the window and driving around. It would at least let me know if there is a faulty wiring connection or bad pump or both maybe. wavering current would indicate something wrong.

 

Well, that may tell you one part of the story, but a plugged fuel filter could act the same way as a circuit problem in terms of the amp draw. Load is load at the fuse.

I guess the two easiest things to try first would be redo the electrical connection and replace the fuel filter. I have gotten bad fuel filters before.

 

Do you have any idea of what the current draw (amps)is on a fuel pump working normally?

Brian