1994 GMC Sierra 4.3 v6 TBI no start
I have good, blue spark - it is getting fuel, timing is set, compression has been tested and is good. Have replaced M.A.P. sensor, engine coolant sensor, new distributor / cap / rotor and new coil + new spark plugs and plug wires. Checked to see if valves were opening, etc, with valve cover off. All seems to be set perfectly. Fuel delivery is also good. The only code I am getting is for low voltage to the knock sensor. This should not prevent the engine from starting. Please help.
How do you know it is getting fuel? You would need someone turning the key to start, turning the engine over to see if fuel is getting threw the fuel injectors. Try spraying some starting fluid down the TBI or just a very little gas and see it it starts.
I have some help - we can watch the TBI sending fuel while cranking engine. Have also tried starting fluid while cranking.
Did you check for spark at the spark plugs?
Yes. It is baffling me. We used spark tester along with pulling a plug and watching spark while cranking.
This should be starting. Do you have a timing light?
Wasn't sure if timing light would help when it is only cranking. Will try this later tonight. We have watched valve actuation and checked timing mark along with setting distributor to line up with firing order. Have checked and rechecked firing order.
Ok, the timing light will work while turning it over. Remember to disconnect that brown wire for the timing advance. Make some marks on the timing marks so you can see. If you have the proper fuel pressure, and the compression is around 150 lbs. this should start.
Compression is 150 on all but #4. It is around 125. Will try the timing light to confirm timing with brown wire unplugged. (took a while to find that thing, it was under the dash / glove box area taped to wire loom)
Good. Just so you know the fuel pressure should be 9 to 13 lbs. I mention this because without the proper fuel pressure, it will not start also. If you get to the point of checking it let me know so you can test the fuel regulator.
Found a vacuum leak by chance - internal. Pulled manifold, replaced gaskets, put all back together and set timing w/ light while cranking. Still not starting. Will have to borrow a tool to check fuel pressure. Will see if I can get that done tomorrow... Appreciate the help so far.
Thanks, here to help.
It's running! Finally! On a hunch, we began testing each individual plug and plug wire. We found we weren't getting consistent spark and some were not sparking at all. We tested the wires and they were good. Changed out the brand new plugs for more new copper core plugs and it sprang to life. Either we somehow fouled a full set of new plugs, or, they were bad out of the box. We were only testing #1 to get timing, etc. Thank you for your assistance and your time.
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