I just bought a NICE jimmy for $400, the guy I got it from said he thought the spider needed to be replaced, but I'm not convinced. It will crank right off, and it runs awesome, then once it gets hot, it's like a switch is flipped and it won't idle for more than 2 mins at the very longest, runs good at 2k rpm, and anything above or below is total crap. And NO SERVICE ENGINE LIGHT. I have already:
Checked the TPS and the IAC per chilton manual
Tried the CAT blockage test of removing O2 sensor
Tested the spark output with a testing light
Replaced the fuel filter

When I bought it, it had a fuel pressure gauge attached that read 60

I Removed the EGR Valve connector when it was still too warm to start, and it cranked, stalled, cranked, stalled, cranked then ran well enough for a mile test drive and stalled in the driveway, and wouldn't stay idle, i kept my foot on it to get it up the driveway, but it stalled. Also, the SEL came on when that valve was unplugged, I plugged it immediately back up, cranked it, and SEL went away, but still bad idle.

I pulled the EGR valve out, and it looked rather clean. I cleaned it up good and tested it with a rubber tip air hose, and it held more pressure than i could push to keep the air chuck in place in the bottom hole. Waiting on a gasket for it to come in.


My thoughts:
It is consistently well running when cold, and consistently poor running hot, also it checked good when cold and hot with the plug light, so I doubt its the coil pack.
It has good fuel pressure, but I don't have a gauge myself so I can't check bleed down.
The good when cold, bad when hot is throwing me. I can't understand how the injectors could be subject to such a drastic change due to temperature, but then again, i've never worked with this engine, or any CPI engine.

Also, lower on the list of problems, The T case wants to jump out of 2wd low, and fights me trying to keep it there (its lever shift), and it seems the front diff won't engage. In 4hi, the rear driveshaft will turn the front one, but the wheels aren't affected. Does this truck have locking hubs at all? or is all the locking and unlocking done in the front diff? The axles would turn the wheels when all this was engaged (was on a rack) but still no effect on the driveshaft or other wheel.

Sorry for the uber post, I've just not found another FOLLOWED THROUGH thread about this. If you're gonna take the time to ask, and you get it solved, it saves everyone else time to POST RESULTS PEOPLE.

Anyway, Thanks in advance, I'm loving this site!

 

The CPI spider is always annoying. I cannot understand why GM went with this design. It does sound vaguely like this could be your problem. When my CPI started leaking it ran fine when cold and poorly when hot, but it was damn near impossible to start it when it was cold. Since it is such a pain to replace the CPI, I would suggest you invest in a fuel pressure gauge that has a long lead hose so you can monitor the pressure from inside the car or put it under a wiper to view through the windshield while driving. Check how long it holds pressure after shutting it off. Do that test while cold and while hot. My CPI problem was the injectors themselves, but I have heard that there have been problems with the body cracking also. That could be temperature related. As for your 4wd problem, I have to defer to others since I have no experience at all with floor shifted units.

Basic questions,
How many miles?
What do the fluids look like? (Engine Oil to diffs)
What is the condition of the tires? Tread depth?

-William

 

It has 141k miles, didn't check anything but the engine and trans oil, the tranny was good, the oil was a little dirty but not burned. The tires are pretty much new. I definitely got my money's worth lol. I just got to find a fuel gauge cheap... thanks for the insight, I'll try that asap.

 

Might have vacum problem Correct me if I'm wrong

 

Fuel pump tester

$19.99

 

Ok, put the egr valve back on, no change. Thanks for the fuel gauge tip, picked one up today, and after five miniutes, it's not dropped at all from 59 psi. Not even a hair. I'm still looking at it, and it's at 59....

Edit:
Checked when hot, also just starting to drop, 57 psi now

Update:
Had to start it with ether, while running fuel pressure stays between 50 and 60, and as it starts to die, it goes toward 60...

Update 2:
Pulled the plenum, looks grimy on both sides and had a little oil on the driver side. The gasket looks new and the couple of poppets I pulled looked like new brass. There was a lot of gunk built up on the wire, but the wire seemed fully intact and the connector was on there right. I'll attach pictures later. Also it seems that it idles fine cold, but it doesn't really run any different than how it does hot, unlike how I thought it ran good cold.

ALSO: the pcm is not in it's original home. Don't ask me where it is, but the only sign it was ever intended to be there is the screw holes where it mounted to the engine coolant tank. obviously it's somewhere because the truck runs, but its not where it was 16 years ago.

 

The ECM was moved?? I cant imagine why. I would say step one would be to make sure there isnt a midget touching wires under the dash to keep this thing running. Once you locate the thing, check all the connections. This opens up a WHOLE new can of worms. If the wires were not connected perfectly (soldered, shrink-wrapped and moisture sealed) then there could be any number of shorts or opens that might cause this kind of problem. If the harness has a bunch of crimp connectors in it to relocate the ECM then my best advice is to go to a junk yard and see if you can get an original engine harness to replace it. There is only one of the four ECM connectors that is part of the body harness. The other three go just to the engine.

Good luck!
-William

 

Lol, it seems profesionally done honestly. There is nothing but clean plastic harness conduit where I expect the connectors to come out. The SEL comes on when I turn the key over before starting and I can unplug the egr valve and let it run and the sel comes on then. Next time I'm working on it, I'll try to find it, lol

 

 

The ECM wasn't moved. 1995 was the transition year from OBDI to OBDII. You could have either operating system on your truck- or OBD 1.5- some OBDI stuff and some OBDII stuff. If the ECM is mounted on the coolant recovery tank it's OBDII. If it's not there it's in the pass side kick panel and it's either OBDI or OBD 1.5. There doesn't appear to be any leaks in the plenum so that's good. When the CEL light flashes what code does it flash?