91 GMC Jimmy Stalls

I have a 1991 S15 GMC Jimmy 4x4 (4.3L V6), and it is running perfectly... for about 30-45 seconds :-(
On a cold start, the engine purrs along and no problems are detected.
After about 30 seconds though, there is usually a preliminary half-second stall, that the engine recovers from. Then about 15 seconds later, the engine dies. Attempts to restart fail, usually just flooding the engine with no sounds of even trying to fire.
To correct this, I have tried the following:
- New spark plugs/wires - New distr. cap/rotor - New air filter - Test ignition coil resistance according to Chilton - test SAT - Test pickup coil resistanve according to Chilton - test SAT - Test MAP sensor, disconnected..no change - Read ECM codes, none (just the 12 "all good" code)
I'm kind of at a loss now. I am getting a nice (perhaps too nice?) spray of fuel into the throttle body when it won't start, and the only thing I can think of to do tomorrow is to test each plug for adequate spark when it won't start.
Since the engine runs perfectly on start up, I'm suspecting "something" cuts or diminishes the spark, or increases the fuel mixture too much, when the system goes into normal idle mode. Either that, or something in the input voltage to the ignition coil is flakey(like the switch/wiring), and cutting out when the system is warming up. Any other ideas?
I shudder to think it may be something in the ECM itself...although there aren't any codes coming out of it, so I'm hopeful there.
Any help, here or in email, would be greatly appreciated. I'm kind of under a time constraint with this, as I wanted to take the family up to Canada for the holidays, and the weather up there is calling for my 4x4...
Thanks! joe snipped-for-privacy@charter.net
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
joe snipped-for-privacy@charter.net (Orko) wrote in message
Sounds like a bad EGR valve. Drove me insane on my '88 S10 for weeks. Do you do short-distance driving or long-haul? If short, your EGR is probably dirty/clogged/jammed/on vacation and needs to be cleaned or replaced.
-The Lonely Grease Monkey 1985' K5 305CUI TH700R4 NP208 KJ's successor
"Ignorance is preferable to error; and he is less remote from the truth who believes nothing, then he who believes what is a wrong." - Thomas Jefferson
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good guess KJ! Either that or the ignition coil is in fact shot; I've seen TOO many bad coils test ok ohm-wise................no way to really test an ignition coil other than replace it. I would also take the ICM (ignition control module) to the parts store and have them run a REAL test on it (you can't test an ICM for shit with a DMM). I'd also run resistance checks on the pick-up coil when the ICM is yanked.
Doc
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

seen
an
(you
I'm going to be verifying the input voltage and the line from the coil to the ignition module tomorrow. Will let you know, but the coil is suspect... it *is* the only high voltage side component left that I haven't replaced ;-)
-- orko
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Doc's the winner!! It was in fact the ignition coil, the last of the high voltage components to be replaced in this adventure. I guess with the new plugs, wires, dist. cap/rotor, there was too much current for that poor old coil to handle ;-)
THANKS everyone for the excellent help in this, here and off-list.
-- orko
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
pde_on snipped-for-privacy@hotmail.com (Lonely G-Monkey) wrote in message

Thanks LG-M, I'll see if I can test this (if I can) tomorrow. Since that valve is basically letting in exhaust gasses into the intake manifold to reduce combustion temperature, and is only actuated when the engine reaches normal operating temperature, this seems like it could be a good lead!
I'm thinking that if I pinch off the intake manifold side hose of the EGR valve, and the engine continues to run (albeit with higher NOx emissions) past warm up, that this would be a valid test. Is it?
-- orko
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 17 Dec 2003 17:13:56 -0800, joe snipped-for-privacy@charter.net (Orko) wrote:

a better test would be to take manifold vacuum and apply it directly to the EGR valve (i.e. bypass the solenoid) if the engine starts running really bad and/or stalls... the EGR valve is most likely OK. if nothing happened and you actually have a vacuum signal, the EGR valve is either A. leaking so bad opening it doesn't make a difference, or B. it's completely plugged up. either way it would be bad.
another route is.. if it's the original valve, replace it, it *is* shot.
-Bret
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

also, the EGR valve is only commanded at cruise to allow more timing to increase mileage and decrease NOx emissions. at WOT the EGR valve is closed, not that there'd be enough vacuum to open it anyway.
-Bret
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Will do. I'm pretty sure it is.
-- orko
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.