'97 D1 stalling/idle issues

[pdXDisco97]

The ongoing saga of my repair continues...

I recently replaced the transfer case in my '97 D1, 119k. The tcase is working great (although the shifter has changed position slightly...), and I resolved my speedo not working (the VSS crumbled upon inspection, new one installed).

Now there's a new issue:

When the engine is warm (after driving for about 20 minutes) and then shutting it off, if I restart within 5 minutes of shut down the engine dies. I changed the fuel filter because it looked like it hadn't been changed in a long time, but it didn't seem to change the symptom. I've adjusted the idle speed slightly, and that seems to help, but now the RPM randomly goes from normal of 750, jump up to 1250-1500, then drop back down to 750, sometimes dipping to 500. When it dips to 500, is almost dies but not all the way. I took it for another drive and now when I'm stopped and hit the gas the RPM go from 750 to 400-500 and it hesitates and then goes. It is not dying on me now, but I don't really trust it.

Is it the MAF? Throttle position sensor? Fuel Pump?

It seems that it could be any of the above. Thoughts?

 

[1920SF]

What's the fuel pressure? Have you pulled the plate covering access to the pump to check on the connections? Your XD sat for awhile right? I'm guess fuel pump is dying.
R
Ray

 

[pdXDisco97]

Yes, it sat for about 5 months. I don't know what the pressure is, but I have a sinking (funds) feeling that you're right. I'll have to have it checked out.

Thanks!

 

[pdXDisco97]

...I did pull the plate and the connections looked good, but I'm not sure how to diagnose further.

 

[1920SF]

What's the pressure at the rail? Gauge for that is cheap and worth having on hand. Depending on pressure (there is about half a million posts on Dweb regarding fuel pressure/fuel pump dying/etc) that could be an indicator. No reason to drop big cash on a replacement, just replace the motor inside the caddy-also something well documented on here.

The other thing that comes to mind is your stepper motor-may be worth pulling that out and cleaning it good to ensure it's not gunked up.

 

[MonLand]

Does this happen if you unplug the MAF? [Unplugging the MAF will put the truck in limp mode and ignore a lot of sensors]

I had an issue with mine which yield to the engine revving up and down pretty bad making the truck hard to drive; no CEL. Worst was when driving (the up and down rpm thing). This was "simply" the IAC valve that was dead and the ECU was trying to compensate with more/less fuel. I think this was worst when the engine had warmed up (and I -think- I had a slightly higher-than-normal idle speed when cold).

 

[pdXDisco97]

I unplugged the MAF and it didn't seem to make any difference. What would that indicate?

 

[pdXDisco97]

Today's progress. Finally got a fuel pressure gauge, I was at about 20 psi. So I decided to tackle the fuel pump, thanks to instructions on here it only took about an hour and $70. The new one is measuring 34psi, so that's a nice improvement.

She still stalled on me a bit and when I hit the gas the idle would stick at about 1600 rpm. I took it on a quick drive and after that adjusted the idle speed to 750. I started it up twice with a little bit of hesitation around 600 rpm but then it picked back up to 750 and held steady. Could the TPS still be causing this?

Another theory is the gas has been in the tank since March. Any validity to that theory?

 

[1920SF]

You clean/replace the stepper motor?

Fresh gas can't hurt, but I'd confirm the ICV (stepper) is clean. I'd also confirm/deny that the wires are good, check for arc from the coil, perhaps change the fouled up plugs, and the like. Downside to having her sit for a long time, and then start running like crap when she gets back in the fight.
r-
Ray

 

[pdXDisco97]

Thank Ray, the more I think about it, the more I think your assessment is right. I'm going to clean every thing, and probably put new plugs in as well, just to be sure.

It's great to have it back on the road! With seat covers and all...

 

[1920SF]

Joey-
Looks good back on the road! I would treat her to some new plugs since that's cheap and while you're doing it you can see how they look one by one to see what it's burning like. Cleaning the stepper is fast and worthwhile too. Trying to find ways not to throw lots of $$$ at it while still working through all the possible reasons for an air/fuel/spark imbalance.

Can't believe you still have the hydraulic step on the back. Also can't believe LR put the US flag on backwards.

 

[pdXDisco97]

I added the step because I've got four small kids that have to climb into the jump seats. It'll come off once they're bigger.

And I get a lot of grief about the flag, but I plan to add a snorkel someday, so it'll get removed and replaced with proper US flags on both sides.

 

[1920SF]

Ah, makes sense on adding the step-I assumed it was there since new and I was surprised. If you put it on later it tracks that it is still working....

Mostly messing with you about the flag-if you go snorkel, get the mantec-it is worth it even if you have to cut the fender.

 

[pdXDisco97]

Well, if you look close there's a bungie cord holding it up. still need a low profile rack. A 2" lift is next on the list.

I put in new plugs, sprayed the ICV with carb cleaner, put a fresh tank of gass in, she's running pretty good, but still a bit rough. I'm going to drive her a bit this week and then camping next weekend, we'll see if the stalling goes away.

Thanks!