I have a 94 s10 blazer tahoe LT with a 4.3L W CPI. I've ran myself crazy and broke trying to find out why this truck just won't run right. I dropped the tank and its clean new strainer, pump is working, I replaced every sensor but the knocks, new exhaust, filters you name it. I finally got it to fire when I replaced the fuel pressure regulator but it runs rough. It only wants to run when its cold in about 10 min after the engine warms up it starts bucking and sputtering and stops running all together until I let it cool down to cold again and only starts with a blast of starting fluid. I have the digital dash cluster and get no temp reading at all. I know the dash lights work because I can see them when I turn the key on so I though it would be the temp sensor, replaced that still no good. i tested the yellow wire as far as I could and nothing so I went and got a new computer and still does the same thing. Can anyone please tell me what I'm missing or what to look for, I love my truck but I can't afford to throw any more money into it until it can get me to work. Oh and can anyone please tell me why every other blazer I looked at in the parts yard has 2 computer boxes behind the glove box and mine seems to have 3.

 

Have you tested the fuel pressure? If so, what was the pressure reading, in PSI, and how long did it hold this pressure after the pump shut off?

 

I have no pressure gauge I guess I should get one. is there any way to tell if thats my problem without one? I have no other vehicle and I take a risk of being left on the side of the interstate again every time I go to the parts store. and thank you.

would fuel pressure cause my temp problem? because it only acts up after it gets warm.

 

The injection system used on the engine in your truck has a very specific requirement for pressure; 55-60psi. It really isn't something you can measure by pushing on the port and seeing how high the fuel squirts!

The gauges aren't that expensive.

You have basically already narrowed it down to a fuel problem. You just need to determine where to concentrate your efforts. I know you said that you replaced the FPR, but when you did, did you inspect for leaks before buttoning the intake back down?

It could be a leak internal to the plenum that may make things worse once up to temperature.

 

when I opened up the plenum it was a black mess I cleaned it out as best I could. There was about a thimble of fuel on the bottom but wasn't there when I opened it to recheck about a week later. the egr valve and the port coming up from it into the plenum was completely blocked up with stuff so hard I had to chisel it out. I replaced the egr and she liked it. sometimes she starts no problem(only when she's cold or close to it) I'm going to get a pressure gauge today. also the pressure relief or check valve behind the plenum gets wet sometimes I checked the core it seemed fine tightened it up and it didn't do it again until about a week later. This is my first venture into this type of system. could you tell me if maybe my digital temp gauge not showing anything could have something to do with it acting up when it gets warm? the sensor is new and the gauge itself seems ok it goes all the way up and down when I turn the ignition on.

 

If the ECU is still feeding it fuel like it's cold, it could cause the problem you are experiencing. The sending unit for the ECU should be located at or near the thermostat housing.

 

swartlkk thank you again for your help. I'm sorry if I'm using the wrong methods of posting my comments I'm new here. I love the forum, its a resource people like me are looking for when we search for help. Not sure what the ECU is the only thing in that area is what I thought is called the coolant temp sending unit which I replaced the other day with no luck. I think my problem may be a wiring issue but I'm not very good with a tester. Could you please tell me how to test the circuit. The wiring harness goes behind the engine and splits down below where I can reach. I checked the harness going from it up above the brake booster and no yellow wire so I guess it goes the other way through the firewall under the glove box but 3 yellow wires come out, one into each of the 3 comp boxes I have under there. I get partial cont on all of them. and what is this 3rd box under there that I don't see on the ones at the yard?

 

You need to get a multimeter and test the continuity between the ECT sensor and the ECU. Here are the pertinent wiring diagrams:


Also, you can test the ECT sensor for proper resistances.

Temperature *F (*C) --> Resistance (Ohms)
212(100) --> 177
158(70) --> 467
100(38) --> 1800
68(20) --> 3520
23(-5) --> 12300
0(-18) --> 25000
-40(-40) --> 100700

 

have you touched it with your hand yet? lol i just had to say it,

 

What?