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Old 09-30-2019, 11:11 PM   #1
ewrjontan
 
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Default Truck dies after warmed up (VG30E) and other issues.

Alright, so first things first. I have a '94 hardbody SE Extended cab with a VG30E and 218,000 miles or so.

* Fuel pump was supposedly replaced by the previous owner fairly recently.
* Timing belt, drive belts and spark plugs were just replaced and the wires look relatively new.

Drove it for 13 miles after I purchased it before taking it apart to do the timing belt so I have no idea if these issues were before or after my timing belt job lol.

After first getting the car back on the ground, the car seemed to be running ok but would surge/buck if I tried to go above 3000 rpm along with some belt squealing. As well as a high idle (around 1500 rpm).

I tightened all of the belts to get rid of the squeal and the truck was running like a champ (other than the high idle) up until recently.

Last week I was a minute from home after a 20 minute commute and I lost power in the gas pedal. I would press it and nothing would happen and the RPMs would just slowly drop. RPM's went below 1000 and the truck would stay on and eventually die.

Cleaned the MAF, as well as my ICV (just the part that is accessible without removing the intake plenum). Truck was running poorly but it's because I forgot to plug the MAF harness back in. Plugged it in and it worked great. Took her out again and the same thing happened (except this time it was in traffic).

Lost power and nothing would happen when I press the gas pedal. RPM dropped and truck eventually died. If I waited 5 minutes or so I was able to start the truck up again and go a few miles before it happened again. Died, waited a few minutes, drove a few miles, died, waited, rinse and repeat five times and eventually made it home.

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So it seems that the issue occurs when the car is WARMED up. Seems to run perfectly fine for the first 15-20 min or so before this starts to happen.

I have noticed that occassionally if I go above 3000 RPM the truck will still buck, but this is intermittent. However, i try not to go above 3k too often for this reason.

I checked the codes on the ECM and it looks like all I have is a code 34 (Knock sensor). Is this something that would cause this? I am hoping not since I would rather not have the car down if I can avoid it.

I have already ordered and will be replacing my throttle position sensor in case this is the issue.

I am assuming this could also be a timing issue as I have not attempted to adjust the ignition timing and seems to make sense if this is occurring after the vehicle is warmed up. Does this sound like it could be the culprit? Now I have some questions:

1) I have a high idle; it is around 1500 rpm. Is it necessary to adjust this first, before attempting to adjust the ignition timing?

2) The ECM switch has an "idle adjustment." How is this different than adjusting from the air idle control valve?

3) I have included an image of a harness on the passenger side of the motor that is unplugged (and has been since I got the vehicle). Does anyone know what this harness is supposed to be plugged into (its right below the ignition coil)?


Last edited by ewrjontan; 09-30-2019 at 11:17 PM.
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Old 10-01-2019, 01:32 AM   #2
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No idea about the plug but injector? It's in the right general idea?



Don't mess with the idle yet.



The fact it stumbles around 3000RPM makes.me think it's in limp mode. Check the TPS, MAF and the knock sensor. I'd check the knock sensor first. Got a copy of the FSM?
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Old 10-01-2019, 02:16 AM   #3
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You can unplug the knock sensor harness and check the resistance without removing it (which is a PITA).

It sounds like you have an intermittent faulty electrical connection. When it fails, the ECU sees it and goes into limp mode.
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Old 10-01-2019, 02:32 AM   #4
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I have a copy of the FSM. Ill be replacing the TPS later this week and will probabyl go ahead and replace the knock sensor Does this sound like a timing issue at all? Before I go and spend the money on a timing light.
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Old 10-01-2019, 05:18 AM   #5
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Actually, the knock sensor is on the block, below the intake plenum. It's a job to replace.
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Old 10-01-2019, 10:08 AM   #6
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I’d set the timing before I replaced anything.
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Old 10-01-2019, 08:18 PM   #7
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Kind of what I was thinking. I’ve read about tons of people driving around fine with bad knock sensors.

So do I try and adjust the idle first and then do the timing. Or timing first then work on my high idle. And how does the ECM idle adjustment differ than the idle control valve adjustment?
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Old 10-01-2019, 08:29 PM   #8
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If the timing is off, it can create the fast idle.


Loosen the distributor and turn the timing to what it should be.

I never had much luck turning up or down the idle using the ECU control.
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Old 10-01-2019, 10:24 PM   #9
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Advanced timing can do fast idle too. I run about 27degrees on my truck (don't recommend you try that high) and I can often have a slightly high idle.
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Old 10-01-2019, 11:51 PM   #10
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Mine is in the +20 degree range and it has a higher than normal idle. But since it is carbed, it is an entirely different animal.
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