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Keeps shutting off and will not start for a while

Tiny
BRCOPELAND
  • MEMBER
  • 1991 CHEVROLET SILVERADO
  • 4.3L
  • V6
  • 2WD
  • MANUAL
  • 119,000 MILES
I'm completely lost. I've replaced the coil, wires, plugs, distributor cap and a rotor. New fuel pump and sending unit. New fuel filter. Truck will run and idle good for awhile then it will bog down and then shuts off. Once that happens its extremely hard to restart. After a few hours it will fire right up. While driving it will run pretty well. Until you go to stop then sometimes it will shut off. And again very hard to restart if it will at all. Oil is new. There is no white smoke or milky looking oil to indicate piston rings. I pulled the IAC and it was black. Cleaned it and still nothing. Please help. Thanks
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Friday, September 13th, 2019 AT 2:58 PM

18 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Welcome to 2CarPros.

Have you checked the pick-up coil and ignition control module in the distributor? It sounds like it is related to one of them. Often times the ICM will fail internally and be affected by heat. The pick up can become corroded and not make proper references.

Let me know. I attached a picture of the distributor below. I circled the two components I am referring to.

Take care,
Joe
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
Would it still be getting fire if that is bad? Because I checked and it's still getting a good spark.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Welcome back:

No, if it was bad, you would lose spark. Have you checked and confirmed fuel pressure and checked for an injector pulse when it happens?

Joe
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
I checked both the pickup coil and the ICM. The pickup coil showed a reading of 861 on the meter. I took the ICM to be checked at O'Rielys and it failed multiple times. Going to replace that today and see if that doesn't fix the problem. Fuel pressure is soiled. The ICM starts to fail when it gets heated up so I'm hoping it will fix it. I also had to change out the EGR valve due to it was stuck in the open position.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
Okay, so I changed the ICM out drove it about a block and it shut off again. And wont start back up.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Have you lost spark?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
It did lose spark today.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Welcome back:

I can't be 100% sure, but it sounds like the distributor is bad. If there is excessive play in it, it will affect the pick up. Do you have a different one you could try?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
No, I don't have a different one to try. Maybe I can get one from a junkyard and try that and see what happens.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
The only reason I am saying that is because there could be play in the shaft. See if there is excessive end play or any left to right play.

Let me know.

Joe
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
Distributor does have play in the shaft. I pulled the codes and map sensor came back on 2 different ones.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Welcome back:

Okay, have you checked the MAP? What are the specific codes you are getting?

Let me know.
Joe
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
It showed map sensor signal out of range high.
And map sensor out of range low.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
As far as the sensor signal, here are directions for testing it. However, it requires an OBD1 scan tool.

_________________________

Pic 1

Pic 2

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Checks MAP sensor output voltage to the ECM. This voltage, without engine running, represents a barometer reading to the ECM.

2. Applying 34 kPa (10" Hg.) Vacuum to the MAP sensor should cause the voltage to be 1.2 - 2.3 volts less than the voltage at Step 1. Upon applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.

3. Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected tot he MAP hose.

Let me know if that helps. If you can provide the code or codes you found, I may have a specific diagnostic flow chart for it. Otherwise, this is what I have.

I hope it helps. Let me know.

Joe
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Thursday, September 3rd, 2020 AT 9:39 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
Okay, so went ahead and put a new map sensor on. And a new distributor. Same problem is happening. Once truck gets up to running temp. It stalls out and dies. I've replaced everything in the ignition. Don't know what it could be now. I'm completely lost at this point.
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Thursday, September 3rd, 2020 AT 9:39 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Welcome back:

This is a tough one. We need to start over and think about what has been done, recognize the symptoms, and determine what needs done next.

Can you confirm that both spark and fuel are lost when it won't start? Is that still the same as before? You mentioned the map sensor code and two different ones. What are they? Also, can you provide the code number you found?

I have a stupid question. Has the distributor cap been replaced? I've seen them with cracks that expand when they heat up and kill the engine. I realize it's a long shot, but all the typical things have been covered.

Let me know.

Joe
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Thursday, September 3rd, 2020 AT 9:39 AM
Tiny
BRCOPELAND
  • MEMBER
  • 28 POSTS
Yes. I've replaced the distributor, pickup coil, icm, ignition coil, wires, plugs, distributor cap and rotor. Also replaced the map sensor. The code numbers were 33 and 34. I also rest the timing. Still having the same issue.
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Thursday, September 3rd, 2020 AT 9:39 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Welcome back

Do you have an OBD1 scanner that can read live data info? If so, let me know. I will get the flow charts specific to each of those codes. I will need to know if you have a 4L60 or 4L80 transmission. Since it is the 4.3L, I suspect it is the 60, but if you can confirm that, it will be helpful.

Let me know.

Joe
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Thursday, September 3rd, 2020 AT 9:39 AM

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