I've tried doing my due diligence via Search here on the forums, but, everyone's similar issues are different enough (to me) that I can't apply their remedies to my situation. So, I'm wondering if you guys would indulge me.

My beloved 88 B250 (318) conversion has been running beautifully until recently. Two different mechanics are stumped and/or are unwilling to really get in there and suss out the problem. I'm left to figure out what to do now (keep it, sell it, take it to a dealer), but, wanted to run the symptoms past you guys first. Here are the deets:

No codes thrown.

The van starts fine. Idling in Park/Neutral, it's extremely rich and unstable until it warms up. Once warm, it sounds normal, but, it won't take the gas you give it. It bogs down.

Things get even worse when you put it in gear. Not only does it almost stall, but, constant fuel will send the engine in to a stuttering, bogging, bucking, high revving fit and back. Just horrible. I can drive it, but, it feels like I'm getting about 20% power with intermittent spurts of it "catching up" to the gas I'm giving it.

Eventually, after about 4 or 5 miles of driving like this, it miraculously starts to run pretty much normal. But, man, that's a sketchy 10 minutes of driving.

Alternately, I could sit in the driveway for 10 minutes or so with it in Drive and the brakes on and work it through it's troubles with with the gas pedal, but, I don't think that's very healthy for the van (or my neighbors).

It's as if you have to force it through this in-gear spastic stage before the computer finally figures out how to get it running right. If the engine has time to cool down (sitting overnight/long period), it's back to square one again.

I can verify that it has proper fuel pressure and the coolant temp sensor has been replaced in a last-ditch effort (but to no avail).

I love the van, but, I don't think I can afford to take it to a dealer. I'm debating on keeping it and driving it as-is, or, painfully kissing it goodbye.

Do these symptoms sound familiar to any of you?

 

They are fairly similar to when my ('89)ECM was failing. Usually dead cold starts were fine, but then I'd drive 1.5 miles, park for an hour or 2 then the van would start, and stumble. The relays would be clicking away, the check engine light flashing on and off, and I'd have to feather the throttle for it to keep going, backfiring, popping, and then after 15 to 45 seconds of this, like someone flipped a switch, it would run perfect.

It is said you can confirm a diagnosis by heating the ECM with a hair dryer first, and seeing if the symptoms dissappear.

Also look to see if any wires going to your transmission have been chafing away in the wind on the tranny bell housing, that's what made my ECM fail.

 

Do you know which coolant temp sensor was replaced, the 1-wire one or the 2-wire one?

Have either of the mechanics tested the EGR valve for proper operation?

 

Oh ho ho ho ho...you thought you were going to slip that one past me by burying it at the end of a long response. Better luck next time Mr. Wire Whiner!

 

Ugh...you know what? I just got back from picking it up from the mechanic and didn't know there were two different temp sensors. Dang. I know it was a $45 part, if that helps.

I will add that there is a rattle in the undercarriage [that I suspect is the cat converter] that seems to disappear once the engine starts to run "fairly normal" <--which is relatively speaking. (I think "driveable" is probably more accurate a term.)

Does it make sense that a cat converter would need to get hot to make things run better???? And I know a failing cat is a byproduct of another problem usually.

 

I ended up taking it to the Dealer. I did NOT want to do that, but, it's worth it to me to have someone who [supposedly] knows these engines to look at it.

My service writer called yesterday to let me know that they've moved the vehicle from the "engine" guys to the "tune" guys, since the former couldn't pinpoint anything. He called back to let me know I have at least one arcing plug wire and a couple of worn plugs. I reluctantly gave them permission to replace the whole thing shebang (cap, rotor, plugs, wires, etc.). I say "reluctantly" because I can certainly do this myself, but, cannot make the time to fetch the vehicle and get it done before our camping trip next week. They have me where they want me, I guess.

I'm not sure if this will fix the problem. I know it will help, of course, because it definitely misfires. I'm just not sure if it's going to address the fact that the vehicle runs much better after you plow through the rough, first few miles.

Could it be that maybe the ECM eventually does a fantastic job of compensating for the misfiring or something??? Any thoughts???

 

Hi guys. Readdressing this again...

3 mechanics (including the dealer) and still no luck at solving this mystery. I'm going to revise my description of the problem by saying the following and then offering up a theory with the hopes you guys could chime in with a "that could never happen" or "you may be on to something": :-)

The rough idling/bogging period upon start up is accompanied by a rattling near/at the cat converter. Giving the van enough gas in Park first and then in Drive with the brake on eventually gets the van smoothed out and that rattling goes away. It drives fairly normal after that.

I originally thought it was a temperature or "warming up" problem. Now, I'm thinking it's a "constant RPM thing" that eventually smoothes out the van. Does the following make sense...?

A clogged/deteriorating cat converter that 1) Eventually heats up enough to unclog or 2) Is eventually offset by the ECM finally adjusting to the pressure problems created by the converter.

Again, the rattling goes away after the van smoothes out, so, I may be offbase here since heat doesn't seem like it would "unclog" the loose bits and whatnot.

Is the thin metal tubing coming out of the cat converter and heading up to the engine one of the O2 sensors? I was thinking of unscrewing it, letting it breathe and seeing what happens. What do you think?

I dunno...grasping at straws here before I decide to sell it or not.

 

Yes try taking out the O2 sensor and see if the van starts up better. Do not drive it with the O2 out but just idling in the driveway should help determine if the cat is clogged and causing this problem.

 

I'll try that. Thanks for the input.

 

Buckaloo- I have a 99 ram 1500 and am having the exact problem with mine. It has been it shop for going 3 weeks with no end in sight. They replaced the dist, wires, etc. and it still does it. My alternator was cracked and sticking upon starting (but it still worked), so I told them to replace that and see if that helps. He said that he's only seen that in chevy's but whatever. Hopefully today they will know something. I'll post the results later GOOD LUCK