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Old 12-03-2021, 10:25 PM   #1
Boog
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dies randomly at idle in gear

My truck sometimes just dies while idleing in gear, even with the A/C off. It starts right back up easily. There are no stored codes. No obvious vacuum leaks.
This 91 sportside I recently bought is 350/auto and I have been replacing some parts I am sure are at least 25 years old. A little tuneup at the actual 82,300 miles.
I rebuilt the tb (nice conical spray pattern now), replaced the AC plugs and AC plug wires, fuel filter, ecm's coolant temp sensor with an AC one also, new thermostat.
About those plugs. The underhood label calls for plug gap of 35 thousandths. I gapped the new ones at that and it did not want to run, at all. I have never gapped plugs at 35 on an HEI vehicle, always 45. But I opened them up on this truck to 45 and it runs great. And the random dieing was happening before I began this tuneup.
The truck has been in the local chevy dealer's shop numerous times before I bought it for this and a trans leak they had trouble stopping.
I don't do business with that dealership.
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Old 12-04-2021, 12:34 AM   #2
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Re: dies randomly at idle in gear

Likely a bad pickup coil or ignition control module in the distributor. Napa sells a complete, brand new distributor with a cap and rotor for about $150.
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Old 12-04-2021, 12:53 AM   #3
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Re: dies randomly at idle in gear

Did you use AC Delco original type replacement plugs?
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Old 12-04-2021, 08:05 AM   #4
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Re: dies randomly at idle in gear

Yes.
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69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver
primer is finer
91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said.

I stand for the flag and kneel at the cross
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Old 12-04-2021, 11:04 PM   #5
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Re: dies randomly at idle in gear

Strange. My trucks run fine with the plugs at the proper gap.
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Old 12-05-2021, 03:56 AM   #6
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Re: dies randomly at idle in gear

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Likely a bad pickup coil or ignition control module in the distributor. Napa sells a complete, brand new distributor with a cap and rotor for about $150.
Super common issue on these trucks.
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Old 12-05-2021, 09:21 AM   #7
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Re: dies randomly at idle in gear

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Strange. My trucks run fine with the plugs at the proper gap.
The AC plugs that were replaced were also gapped at 45 so Dad must have been through it too. I wonder if increasing the plug gap makes it fire stronger.

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Super common issue on these trucks.
I am pretty sure it has never had a new distributor. The shaft has no play and all inside looks good. That doesn't mean it is without fault though.

With the few parts I have replaced it starts much easier now where before it spun over a good bit before starting each time, now it starts very quickly. So I am making headway with it.

This is an original, all stock '91 Chevy truck that has never been driven hard. My Dad more or less babied this truck. It has 82,300 miles on it and uses absolutely no oil and seems to be real good on gas mileage though I haven't put the pencil to it. I am reasoning that age is taking it's toll on electrical parts. It seemed to run better by replacing the plug wires alone and they were AC Delco wires but 30 years old. I bought new AC Delco wires to go back on it. My Dad was a stickler for keeping a GM vehicle all GM.
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69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver
primer is finer
91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said.

I stand for the flag and kneel at the cross
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Old 12-05-2021, 12:46 PM   #8
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Re: dies randomly at idle in gear

There isn't much to the engine control system on these trucks and since you did most of it I also would suspect something with the distributor. I've had bad ICMs and pickup coils do strange things. Other than that, it might be doing what my truck was. Mine was dumping the maximum amount of fuel it could into the motor due to improper oxygen sensor readings. The oxygen sensor was good though, I had to add grounds everywhere to fix it.
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Old 12-05-2021, 02:53 PM   #9
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Re: dies randomly at idle in gear

Just replace the whole thing, regardless of shaft play. Ignition modules can fail with age, pickup coils can crack, wear, or have issues with the magnetic portion. You can buy pickup coils and ignition modules, but by the time you add in a new cap and rotor (which you haven’t said if they were replaced or not), you’re at the cost of an entire new unit with a warranty. Aside from the ECM, the distributor provides the most control over the engine on these trucks.
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Old 12-05-2021, 08:52 PM   #10
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Re: dies randomly at idle in gear

Well looking at some dists the Napa one looks to be the best value @ $126 and I trust Napa brand. There are 21 stores around me. I'll check a couple more things yet.
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69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver
primer is finer
91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said.

I stand for the flag and kneel at the cross
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Old 12-05-2021, 09:28 PM   #11
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Re: dies randomly at idle in gear

When my sons went out it was a similar situation but it continued to get worse....more often ..and harder to restart

Btw the pickup also pulses the tbi injectors, that was the tail tale sign. Eventually it wouldn’t restart and upon taking the air cleaner lid off I saw no fuel, did some reading and then replaced the whole distributor
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Old 12-05-2021, 09:54 PM   #12
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Re: dies randomly at idle in gear

I changed the pickup coil only. It was like $20.
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Old 12-06-2021, 03:04 AM   #13
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Re: dies randomly at idle in gear

Quote:
Originally Posted by Boog View Post
Well looking at some dists the Napa one looks to be the best value @ $126 and I trust Napa brand. There are 21 stores around me. I'll check a couple more things yet.
Those are the ones I go with, and to be honest, I now consider it a normal wear part and replace them on every new TBI truck I buy as part of the service/tune up. I think I’ve installed 4 just this year.
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Old 12-06-2021, 07:33 AM   #14
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Re: dies randomly at idle in gear

Those Random problems are the worst

My suspect would be the ground on the ECM.

Had a Baby Caddy that would die at the stop sign crank back and go.

That was what that issue was.

Hope you find the problem
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Old 12-06-2021, 09:48 AM   #15
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Re: dies randomly at idle in gear

Throttle position sensor? I had to replace mine for similar issues.
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Old 12-06-2021, 12:01 PM   #16
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Re: dies randomly at idle in gear

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Originally Posted by Getter-Done View Post
Those Random problems are the worst

My suspect would be the ground on the ECM.

Had a Baby Caddy that would die at the stop sign crank back and go.

That was what that issue was.

Hope you find the problem
I had to ground my computer to the battery, and I had to ground the computer case to the battery.
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Old 12-06-2021, 12:27 PM   #17
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Re: dies randomly at idle in gear

The ecm on these models is located behind the passenger side kick panel isn't it?
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Boog
69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver
primer is finer
91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said.

I stand for the flag and kneel at the cross
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Old 12-06-2021, 03:33 PM   #18
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Re: dies randomly at idle in gear

Mine is behind the glove box.
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Originally Posted by Early Cuyler
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Old 12-06-2021, 05:24 PM   #19
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Re: dies randomly at idle in gear

Ok thanks.
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Boog
69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver
primer is finer
91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said.

I stand for the flag and kneel at the cross
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Old 12-06-2021, 11:18 PM   #20
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Re: dies randomly at idle in gear

If you put your Coffee cup in the Left cup holder it could disturb things

JK
Hope you find the issue soon
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