Engine not running

MARKYB

MEMBER
1992 CHEVROLET TRUCK
V8
4WD
AUTOMATIC
182,000 MILES

Several days ago my truck started to miss. I had a hunch it was some plug wires that were in bad shape. I replaced the plug wires, dist. Cap and spark plugs. The truck would not start, labored the started and would backfire. I of course thought I had botched the firing order. After checking the firing order (18436572) I adjusted the dist. To try and find a position that would at least allow the engine to start and idle.

After many attempts I grabbed the timing light, disconnected the injectors and set the timing to 0-deg. TDC and tried again, no luck. Removed the spark plug wires one at a time to try and isolate a bad plug or wire, still no luck. Set engine to TDC and checked position of rotor, pointing nearly to number one plug on dist. Cap.

At this point I ran a compression check and got readings between 75 and 90 lbs. On each cylinder. Referring to my rebuild manual I see no reading below 101 lbs. In min. Allowable compression. Decided that maybe the timing chain had jumped and removed cover. Timing marks are correct.

I'm out of ideas. Any thing that would cause a miss in the engine, and a complete backfire after new plugs, cap, rotor and wires were installed? I was also unaware that this model truck had an ESC that needed to be disconnected before setting the timing. So after I re-install the timing cover, I'll probable go ahead and just replace the chain and sprockets as long as I'm this far, I'll try and unplug the ESC and try again. I'm also not sure if this is an acceptable reading for compression. I replaced the heads on this engine about 3-5k mi. Ago.

2 Replies

DOCFIXIT

MECHANIC
18,828 POSTS

Compression to low add 10cc oil to each cylinder and repeat compression if it jumps up then rings and cylinder wall wear

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Tuesday, September 12th, 2017 AT 7:06 PM

MARKYB

MEMBER
2 POSTS

OK, will do, as soon as timing chain and sprocket are replaced. I would like to assume that the engine will run with the lower compression as I'm aware that it is "tired iron". I would like to address the original problem which was a dead cylinder or miss.

If you seen the plug wires that I replaced by default you would have agreed that they would most likely be the cause of the miss. However, after changing the wires and damaged cap the miss became more pronounced, so much so that the engine will not run and began to back-fire through the carb. At the time, I assumed that I had erroneously messed up the firing order. After at least 20 checks, it is correct.

I can only assume that I am dealing with an electronic failure of some sort, either a bad component or faulty wire, that originally caused the problem. I will point out that this vehicle was a daily driver in solid shape and performance. Enough so that when the head gasket failed I felt comfortable with investing in a set of refurbished heads rather than a recycled engine. I can handle most repairs other than a trans. Rebuild and I am comfortable keeping this truck on the road for another 100k miles. I do however require some guidance to expedite the diagnosis of the miss as this truck is needed on the road asap.

The engine rebuild will come later when financial demands are not so great in other areas.