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1990 GM 3500 stalls out & won't restart

This is a discussion on 1990 GM 3500 stalls out & won't restart within the Automotive Support forums, part of the Tech Support Forum category. Hello all, First post here. So this truck has a 454 and 3spd auto, (I think it's a TH400) it


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Old 07-10-2008, 08:07 PM   #1
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Hello all,
First post here. So this truck has a 454 and 3spd auto, (I think it's a TH400) it has TBI and the fuel spray pattern appears to be a nice cone when running. It's kind of large droplets at an idle, but when I hit the throttle it sprays a pretty fine mist. Unfortunately a LOT of it, like a set of waterfalls.

The problem is it will just kill sometimes. I've been able to pick up no pattern to how or when it kills other than a 100% shut off. No sputtering or rough idling, just stop. It will to it cruising down the road, under power, holding back, conserving gas down a hill (trans in N, engine idling :) ) It has stalled while idling in park, I think you get the picture.

It started out with this behavior when the weather got hot. I figured since it has a 195 thermostat and the big block it could be vapor locking for some reason, but now it does it on cool days...

Later on I noticed that the speedometer will just stop working while driving. I've noticed it stop working as well as resume working while driving. I replaced that this morning after consulting a garage with diagnostic tool. Still have problems, I did my homework on goggle tonight and counted the flashes of the check engine light. It only comes up with code 24, the speed sensor one.

I don't know if these two issues are related or not. I understand that the ECU does use feedback from speed sensor to help control the engine.

This week I've been driving it to work ~ 32miles 1 way and it would repeat it's cycle based on time, except for today. It would start fine and run, idle and accel fine cold as well as when the temp came up; but after about 15 minutes it would have it's first stall. I could get it started before coasting to a stop. Then it would run for as best as I can count 60 seconds then stall and we'd coast to a stop before it would start. Then it would only run for about 1-2 seconds and quit again, but would start pretty quick and be good for the rest of the commute. It did that morning and night two days in a row. Today it didn't stall after 15minutes, it waited until I was further from home then we almost ran the battery dead patiently trying it for about 15 minutes. Try starting for a few seconds then wait a couple minutes to cool starter. Did the same thing tonight when I was almost home. Oh, and the fuel pump in tank runs for about 15 seconds after turning ignition on or after running starter.

I apologize for the long story, just think the details might help diagnose.

This morning after it finally started (i did nothing but wait it out... don't know what else to do.) I turned around and went to nearest shop with diagnostic tool they rattled off a whole bunch of things including high idle, bad speed sensor, and failure to start. All three I was well aware of. I haven't paid enough attention to the high idle to find any patterns there.

Now to further muddy the waters I'll throw in a couple other quirks that may or may not be related. Windshield wipers will work when they want to. Sometimes right away, sometimes several minutes after I ask them to turn on. Makes no diff what setting of intermittent or fast or slow. They also sometimes like to keep running for a while. I just read another thread here about the washers make the wipers go for 4 cycles, so maybe it's triggering that routine when I turn the wipers off sometimes. I'll pay attention to count how many extra cycles they run. And lastly, one of the previous owners installed or had installed this most excellent bulldog security system. It's a joke with wires spliced in and taped up.. I'm trying to figure out it's model so I can look up a schematic because I have a hunch that one of their high quality inline splices my be killing my speedometer wire. IF it uses that for something.

So if you've read all that and still feel like throwing your $0.02 in I'll be glad to read it.

Thanks,

SammyCD

edit 1: One more thing, since I like tweedeling with carbs, my first instinct was to pull the air cleaner off and get a better look at things. Unfortunately this isn't much help with TBI, except that I can see clearly whether or not there is any fuel coming from injectors. So when it refuses to start I have never seen fuel, and every time that I am able to watch while someone runs the starter I can see fuel start to come before it starts up.

Oh, yep that could signal bad pump or filter. OK, I could be wrong here, but every other fuel filter I had to change would keep up with fuel demand at an idle and deff after several minutes of not running. Last week I hauled two loads of lime with the truck. About 12k lbs plus ~4000lb spreader buggy. Just for a test I held it in second to the floor up a 1/4 mile hill and it never sputtered. I did have to let off after a while and let it shift though. Then go back to town for fuel.

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Old 07-11-2008, 01:24 PM   #2
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not sure if it worth 2 cents but here are a couple of thoughts. Wipers - a have seen many GM trucks, 1988- ?? with wiper problems. Many will start by themselves after a car wash and not work when you want them to. So I guess what I am saying is that this is probably not related.
The fuel spray can be very deceiving sometimes. If you think that this is related to it dieng on you, I would visually compare it to another throttle body engine.
My thoughts on this are two things.
1. It sounds as if there may be a bad ground causing some of the issues that you are seeing.
2. The ignition module under the rotor of the distributor not only controls the spark but also controls the pulse to the throttle body injectors. If the ignition module goes bad, it will cut off fuel to the engine.
Sounds to me that the ignition module may be the culprit for the engine shutting down.

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Old 07-12-2008, 07:30 PM   #3
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http://www.hotrodlane.cc/New%20LS%20...TC%20P1361.htm
this link explains in detail how the ignition control module operates--its for a 2001 camero-, which is the wrong make, but they all perform the same basic functions.
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