Starts rough at random times? Only when cold? HELP!

[wilnutt]

This is my first post. I've been lurking and not finding exactly what I'm experiencing. I'll first describe the issue, then describe what I've tried to remedy the issue with no results.

We bought the vehicle from a guy who gave us information that hid the underlying problems. Within the week it's becoming more of a pain and less than a joy. The more I look at the engine bay, the more I see things that aren't right (The top port of the PVC valve is capped, the EGR vacuum solenoid is unplugged and the plug has been jumped with a jump wire to complete the circuit, there's a port under the EGR valve that is capped. It runs fine when it's warm, but will sometimes start like it has a racing cam and puke black soot and/or backfire under acceleration.

ISSUE:

WHEN IT WILL RUN GREAT: When we start the B2 it will shoot to 1,400-1,500 RPM for about 10-seconds, then it will idle down to around 900-1,000 with a little throttle movement and jumping (Sometimes none, sometimes 200-300 RPM), then I can throw it in to gear and we seem good to go.

WHEN IT WILL RUN HORRIBLY: When we start the B2 it will shoot to maybe 900 RPM and will jump from 600-900 RPM, like it has a nasty muscle car 3/4 cam. While idling sometimes the lights will flicker or it will completely cut out for half a second, revving it up will result in Black soot all along the wall. If we throw it in gear and try to take off, under mild to heavy acceleration it will backfire and run like crap. It will only get better once the vehicle is warm. Even then, ti's not 100%

WHAT I'VE TRIED

-Replacing IAC
-Replacing vacuum lines
-Replaced MAP sensor
-Check the FPR (No leaking fuel or vacuum leaks)


I also checked the ECT sensor today after it started right up and still cold, 50 degrees outside, set at 200k on my multimeter, I get an OHMS reading of 33.5. Does this seem right? I will be checking it again early in the morning when it's around 40 degrees, as my wife and I have a very strong belief that there's a correlation between temperature and how it's going to start (We can only hope there's a pattern and it isn't completely random)

I'm stuck on what to do next. My gut says it's something with the EGR system, the O2 sensor needs replaced, or the ECT sensor needs replaced.

Any help would be awesome!

Thank you all in advance for your help.

-Wilnutt

P.S. i will also be posting this in the 2.9L section. Moderators please make adjustments if needed.

 

[kaidenshi]

I've been having the exact same issue, to a "T", on my 1988 BII with a 2.9L engine. Mine doesn't have EGR so I don't think that's the issue we're both having. You've described my symptoms pretty much exactly though; in any weather colder than 60 degrees it sputters, chugs, runs rich, and lopes like a cammed hot rod. Once it's warm it runs more or less normally with just a slight miss every so often.

So far I haven't been able to track it down, though I've found that I have water getting in the passenger floorboard when it rains. That's where the computer is mounted, so it may be that I'm getting some corrosion on the computer connections. It's either that or a bad ground. I've looked at all my grounds and they seem fine, I don't have any voltage drop that I've been able to find either.

I'm guessing it's still electrical though, because if I turn on my headlights or the blower fan while it's cold and running rough, it will bog down further and try to die. Once it's up to operating temp it isn't affected by electrical draws. Anything drawing directly from the battery (aftermarket LED light bar) doesn't affect it at all, cold or warm.

Here's a link to my post:

http://www.therangerstation.com/forums/showthread.php?t=175395

 

[JerryC]

This will just take a minute, disconnect the O2 sensor and check the connectors. You might find it is crusty. Cold and the connection is poor but since it is near the exhaust the connector warms up and makes a better connection.

Mine was like this, unfortunately I didn't catch it until after I bought an O2 sensor and already had the O2 sensor out. I fixed the connector and replaced the O2.

 

[wilnutt]

Update Testing:
ECT at 48 degrees this morning. 61.5k OHMS. STARTED LIKE CRAP
ECT at 75 degrees the evening. 14.8k OHMS. STARTED LIKE A CHAMP

Thanks Jerry, I've actually bought an O2 sensor a few days ago, just haven't installed it yet. I'll be looking into this in the next few days.

Any other thoughts/input?

 

[wilnutt]

This will just take a minute, disconnect the O2 sensor and check the connectors. You might find it is crusty. Cold and the connection is poor but since it is near the exhaust the connector warms up and makes a better connection.

Mine was like this, unfortunately I didn't catch it until after I bought an O2 sensor and already had the O2 sensor out. I fixed the connector and replaced the O2.

The oxygen sensor actually looks quite new. The connector doesn't look crusty, but half of the plastic is now missing. I guess I'll have to look into how to test the connector.

Adding it to the list.

 

[kaidenshi]

Hey @wilnutt, check this out. Sound familiar? I'm definitely going to go through all my connections and clean them even if they look spotless, after reading this.

http://www.therangerstation.com/forums/showthread.php?t=3623

 

[wilnutt]

Hey @wilnutt, check this out. Sound familiar? I'm definitely going to go through all my connections and clean them even if they look spotless, after reading this.

http://www.therangerstation.com/forums/showthread.php?t=3623

Something I'm definitely going to look into. Of course, now it's warming up, so I haven't had the issue as often. I'm hoping we get one more cold front. lol

Thanks for the link. Def worth a shot! ;-)

 

[wilnutt]

Hey @wilnutt, check this out. Sound familiar? I'm definitely going to go through all my connections and clean them even if they look spotless, after reading this.

http://www.therangerstation.com/forums/showthread.php?t=3623

Of Course now that it's 80+ degrees, it seems to be starting up fine, but with a little 200-300 RPM idle surge that goes away once the tranny is engaged. Sound like a basic TPS issue, but IDC about that for now.

I did run a 14-gauge jumper wire from the existing ground wire/bolt by the computer, to the battery. It looks like someone has been troubleshooting this issue way before I bought it and attempted to do the same. 2 inches from the large ground wires coming from the computer there's electrical tape wrapped around each one {covering a prod from a multimeter?}.

The bolt already had one ground wire and a solid strap at the bolt, is this factory or has someone already added one?

 

[kaidenshi]

The bolt already had one ground wire and a solid strap at the bolt, is this factory or has someone already added one?

I'll have to look at mine again, I don't recall off the top of my head. I didn't get to dig into mine this weekend but my wife is enjoying new glasspack mufflers on her Vic. Happy wife = happy life!

I'll try to look at mine over the next few days and see what I come up with. I'll at least snap a pic of my computer connections this evening and post it, I've already got the panel off and carpet pulled back to dry it out where rain was getting in. I don't know if my dad ever tinkered with the computer on it, he wasn't much for messing with electronics so probably not.

 

[kaidenshi]

So mine has the ground wire as well as a thin ground strap, both look factory and undisturbed.

 

[kaidenshi]

Of Course now that it's 80+ degrees, it seems to be starting up fine

Oh yeah, 82 degrees here when I got home from work today, I decided to start it up after taking pics for another forum post, and it ran like new. We have the exact same issue, I'm positive now. I'm going to drive it to work tomorrow instead of the Yukon and see how it does. I have a feeling it will be like nothing was wrong.

The irony of that is, it's my only 4x4 so it's the best winter weather vehicle we have and it only acts a fool in the winter. Go figure.