Just replaced cps and reinstalled ds4 (attempted db2 swap) drove the truck to the store this morning and it ran great, started right up and no problems. It sat for about an hour, came back out and it fired right up, pulled it into gear an went to pull out and it bucked once then rpms went to 400ish and it wouldn't take any throttle. I pulled it into neutral and revved it and sputtered and never got over 2000rpm. Swapped pmds, checked grounds, reset computer, checked lift pump, bled lines, an checked codes. I got a cps error as well as cylinder balance fault errors. Still same problem. Any thoughts?

 

Have you done a TDCO (pump timing) reset?

The OBDII trucks will do it automatically (if I remember correctly) every 50 start cycles.

I can't remember how the OBDI trucks do it, or if they do it at all. They may just run off the stored value until it's initiated by a scan tool.

 

I dot have a scanner or the cable to use my laptop. I tried disconnecting the batteries for awhile but to no avail. I ended up driving it home. I pulled the optical sensor connector and it still ran like crap but it allowd me to get over 10mph. I didn't turn the motor when I replaced the crank sensor. Just pulled the old one out and put the new one in.

 

The CPS replacement isn't the problem, I'm betting it's removing and reinstalling the DS4 pump.

Here's the thing; as little as 2mm of movement (the thickness of two dimes) on an IP can throw the timing out on a DS4. You're still not safe with less than 2mm, as that also changes the TDCO value.

When you pulled the Optical sensor, you forced the PCM to go to a base timing table and that's why the truck at least ran. It's a sort of "get you home limp mode" built into the PCM.

In order to set TDCO (TDC learn) and confirm base timing (TDC set) on an OBDI truck you need something like this:

Engh Motors - GMTDScan Tech

I know it sucks that you need to buy something to fix the truck, but you need this kind of stuff with electronic injection vehicles. Any of them. It's really no different than needing to buy a specific socket to get a wheel bearing off. You need the right tool to do the job....

OBDII trucks can be done with a key on-key off procedure. Unfortunately, that's not an option for your truck.

Unless you scribed a line on the pump and cover before you took the pump off and lined them up exactly when reinstalled, you don't know where you are for timing of the injection event and I'm betting you're "off" just enough.....

About all I can offer you is to ensure your pump is installed "straight up" (FSOS should be straight up). This should at least get it running halfways decent if TDCO is your problem, but you still need to have the PCM relearn the TDCO value. It changes every time you turn or remove the pump. Disconnecting the batteries will not clear the value, it's stored in non volatile memory.

Then, get yourself a bidirectional scanner (like the one I linked above) and set it properly.

Hopefully, that's your issue.

Other than that, you've either got a failed component on your hands or something is installed incorrectly....

Did it run properly before you tore it all apart?

 

It ran alright before I took it all apart an I wasn't getting a stepper motor fault before but now i am. I did in fact scribe a line where It was set before I removed it. I was getting a stepper motor fault so I replaced the crank sensor and it ran great (I read somewhere online that a bad crank sensor can set a stepper motor fault) its a strong possibility that the pump could be off but would I still be getting these codes for crank sensor and stepper motor? I'm trying to limit the amount of money I throw at this since I have a db2 I'm going to put in as soon as I can figure out why it won't push fuel to the injectors. If the pump was of then I figure it wouldve ran like crap when I drove it yesterday. When I start it, it will run fine for about 10 seconds then go into barely idling and won't rev past 1500rpm.

 

This is information you did not originally give.....recheck every thing you removed/installed.

It may have initiated a TDCO relearn on you and that's why it now runs like crap but didn't yesterday. Mine did that once. Ran fine on a stored TDCO value. It initiated a TDCO relearn and started to run like crap. Little did I know someone had frigged with the pump before I bought it and it had been running on a stored value. Did a pump timing and relearn and all was good again.

But my truck is a 98 and is OBDII. Like I've said, I'm not sure if an OBDI truck will do a "spontaneous" relearn like an OBDII truck....

Take the top cover off the pump and clean the rack that shuts off the metering valve and is controlled by the little solenoid under the cap....the body will be full of fuel but the valve will not allow it into the pump if closed so no fuel to the injectors. The rack needs to slide back and forth freely....they gum up and varnish or time....

 

My apologies, I must've forgotten to include that. Guess that means something has failed in the pump then huh. Looks like visiting a pump shop is next step.......

 

Read my post again friend, I think I was editing while you were typing....

 

Ah okay. The solenoid was clicking but when I pulled it apart it was nasty under the cap. I've got everything about clean and I'll reinstall to see what it does. Can the solenoid be bad and still make that clicking sound like its working?

 

Yup.

If the metering valve won't open, the solenoid will/can still "click" as it tries to move it.

You can see where the "fork" the solenoid moves connects to the rod/rack in the housing. That rack is what opens and closes the metering valve.

It has been known to gum up and /or varnish. Its alao been known to wear a "step" in itself in high mileage pumps. If you had a passle of old fuel in there, it's a fair bet it's just nasty and gummed up.

If the metering valve isn't open, no fuel to the injectors...no fuel to the injectors and.......well, you can see where this is going......


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