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cuts out! now what?


merc81
06-25-2007, 10:41 AM
I've read a couple of old posts where other folks have had this same problem, don't recall any good answers.

My '93 s10 has the 4.3 vortec engine (vin w) with the cpi unit inside the air plennum. I replaced the cpi with brand new including the internal fuel lines. About 2 weeks after this operation, the car started cutting out. It would just die on the road, as if I had turned the ignition off. The first two times it restarted, no problem, but the third time it took about 45 minutes to start up again.
I can't tell what the problem is; fuel or spark. I have a doaner car with the same engine in the shed so I swapped out the spark coil--just in case. I had the spare ECM with me from the doaner the last time it cut out figuring that was the culprit. It wouldn't start with either the orginal ecm or the spare. I did finally get it home with the spare, but I've put the original back in since as I don't see where it made any difference.
My next thought was the fuel pump, but I changed that about 10 months ago and wouldn't expect it to fail already. Checking that out, I measured the fuel pressure at the engine inlet line. I'm getting 50psi at idle. When I rev it up bit the pressure jumps up to 65psi. I wouldn't expect the pressure to change under any conditions since its electric pump with by-pass valve at the injector.
My question here is does anybody know why the pressure jumps up like that, and how about ideas as to why it cuts out? fyi, I installed a new ignition module under the dist. cap just in case. . .

:banghead:

MT-2500
06-27-2007, 08:50 AM
I've read a couple of old posts where other folks have had this same problem, don't recall any good answers.

My '93 s10 has the 4.3 vortec engine (vin w) with the cpi unit inside the air plennum. I replaced the cpi with brand new including the internal fuel lines. About 2 weeks after this operation, the car started cutting out. It would just die on the road, as if I had turned the ignition off. The first two times it restarted, no problem, but the third time it took about 45 minutes to start up again.
I can't tell what the problem is; fuel or spark. I have a doaner car with the same engine in the shed so I swapped out the spark coil--just in case. I had the spare ECM with me from the doaner the last time it cut out figuring that was the culprit. It wouldn't start with either the orginal ecm or the spare. I did finally get it home with the spare, but I've put the original back in since as I don't see where it made any difference.
My next thought was the fuel pump, but I changed that about 10 months ago and wouldn't expect it to fail already. Checking that out, I measured the fuel pressure at the engine inlet line. I'm getting 50psi at idle. When I rev it up bit the pressure jumps up to 65psi. I wouldn't expect the pressure to change under any conditions since its electric pump with by-pass valve at the injector.
My question here is does anybody know why the pressure jumps up like that, and how about ideas as to why it cuts out? fyi, I installed a new ignition module under the dist. cap just in case. . .

:banghead:


Fuel pressure specs is 55/61 on your engine.
Pressure changes according to engine vacuum.

Full vacuum you should see around 56 lbs lbs of pressure.
Full load or low vacuum 60-61 lbs.

50 lbs at idle is to low.

You fuel pressure is to low.
Specs on it is 55/61 lbs of pressure
Here is some guide lines of fuel pressure checking.

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 55-66 fuel pressure.
Cold start should be 55/62 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 55/62 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
If pressure does not come up with return line pinched or blocked off.
Go to fuel filter and hook a gauge direct to a line at fuel filter.
Pressure should come up to 75 or more and will hold after fuel pump is turned off.
If it leaks down there after fuel pump is turned off it is LEAKING BACK THREW PUMP CHECK VALVE OR PUMP MODULE LINES.
Post back your fuel pressure readings.
MT

woody6725
07-05-2007, 02:19 PM
i agree with the pressure being too low. went through that years with my 94 blazer. had about 50-55 pounds of pressure (which you would think was plenty) but it's not. did you use an aftermarket pump? i've heard bad things about most of them, so spend a little extra and get a gm one. good luck

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