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GM TBI help needed

jimmyleetn

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Let me give you a little background to start. I've had the truck (1988 Blazer) parked for 6 months. I've been doing a lot of suspension, steering, brakes, and drive line work. Fired it up Friday and it ran but not great. I had problems before I parked it with it getting hot and then not wanting to start. The engine would turn but it wouldn't run. Talked to a friend he said to try an ignition control module. Picked one up at AutoZone and a rotor button and put them in the distributor yesterday. Fired up the truck and it ran fine. I drove it about 10 mi and parked it. Got ready for the second shakedown run and about 5 miles I went over a dip in the road and a loud bang from the engine and I lost all power. I initially thought it was a drive shaft because my angles are terrible at the moment but that wasn't it. I've been able to get it to start since then but it will not run very well sputters tries to die. No way you can put it in gear without it dying. If you rev it real hard it backfires and blows black smoke. The first place I checked was the distributor cap and sure enough it was real loose. I thought that's a simple fix so I tightened it. Fired it up just now after tightening the distributor and it still ran horribly. Took out the new ignition module and put the old one back in. Still runs poorly. Where should I check next? Do you think it's jumped timing? Timing or another sensor are my two guesses. I just don't even know where to start. I'm not used to TBI. I grew up with carbureted motors on these old trucks. Once I get around to the replacing the motor the TBI and all this stuff will be gone anyways.
 

Wes Harden

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Yes it very well could have jump time.
But if cap was loose inspect it for cracks and chips rotor too. Make sure rotor is indexed to shaft properly.
If all that is good, pull the distributor and check the gear and roll pin.
 

jimmyleetn

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Yes it very well could have jump time.
But if cap was loose inspect it for cracks and chips rotor too. Make sure rotor is indexed to shaft properly.
If all that is good, pull the distributor and check the gear and roll pin.
The rotor button had a little black soot on it, very small amount. I looked inside the distributor cap and all the points seemed fine. I didn't check for cracks but I feel like they'd be obvious. What will I be looking for on the gear and roll pin?
 
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jimmyleetn

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Yes it very well could have jump time.
But if cap was loose inspect it for cracks and chips rotor too. Make sure rotor is indexed to shaft properly.
If all that is good, pull the distributor and check the gear and roll pin.
I haven't started it yet but I feel pretty confident I found the problem. The old rotor button is the green one. The white one is new. It appears that groove piece snapped or chipped. You can see me pointing to it with a probe. I noticed that it was just loose enough that I could move it some. It shouldn't have any play. I'm going to put the green one back on it and see how it runs.

PXL_20210719_185041903.jpg
 

jimmyleetn

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It's fixed! Just drove it about 200 yards up the street turned it around and brought it back. Chirped the tires getting it positioned where I could back it down the driveway and into the shop. Thanks @Wes Harden for suggesting to look at the rotor button. I would have never looked inside it if I hadn't seen what you typed.
 
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