Mechanics

S10 BLAZER CPI...HIGH IDLE, RUNS ROUGH ACCELERATING

1992 Chevrolet Trailblazer

I have a 1992 S-10 Blazer CPI that idles very fast and surges during acceleration. The check engine light will comes on at times. But after turning off ignition it resets and may not come on the next time. I have been able to get codes in the past jumping A-B terminals under dash. Now the light flashes once then stays on. I had it checked with a scanner and all it showed was it was running rich. I tuned it up recently after an ignition miss that I chased down to worn ignition wire. Replaced cap, rotor, plugs and wires. After this recent problem I replaced EGR valve, TPI sensor, IAC valve, and oxygen sensor. I removed the Intake manifold tuning valve and didn't see any excess fuel in bottom of plenum. So I ruled out a leaking injector line. I also sprayed WD40 around plenum and gasket didn't seem to be leaking. I'm now leaning towards a bad computer. I'm running out of money and patience. Any help would be GREATLY appreciated. Thanks, Randy
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Randrm
July 11, 2006.




I know it is frustrating, but dont let it get u donw to bad. Your truck has a problem, and you WILL fix it.
Have you tested the fuel pressure? It should run between 55-61 psi. I have heard of some return lines getting clogged and causing the pressure to back up and dump the excess fuel thru the injectors. It looks like there is a fuel pressure connection on the fuel inlet feed line. The test gauge can be connceted there, and when bled should give you real time pressure while the engine is running.
That CMFI (Central Manifold Fuel Injector) houses the pressure regulator, and also diverts all fuel to the poppet nozzles. It is located on the lower manifold and may be part, if not all of the problem. When you were able to get the codes for the service engine soon light, what were they?

Tiny
Mikeybdman
Jul 13, 2006.
I had the fuel pump replaced once for low pressure (52 psi) because it wouldn't start. The mechanic told me that it took at least 55 psi to pop the injector poppets, so I sorta ruled out low pressure from the pump. But I understand the regulator is attached to the main injector housing and I don't know of a way to check pressure after the regulator.
That could be the problem.
The last code that a scan showed, that I didn't trip by unplugging sensors, was a rich fuel code from the oxygen sensor. I tried a new MAP sensor yesterday. That didn't help. I'm pulling what's left of my hair out!

Tiny
Randrm
Jul 13, 2006.
I should have went with my first and last instinct. I sprang for an hour labor on diagnostics. It was the computer. Thanks for replying Mickey. Your help will probably be needed down the road.

Tiny
Randrm
Jul 19, 2006.
Hello,
I have a 1993 s-10 blazer with the 4.3 cpi motor also. Mine is running rough after warm up, using ALOT of gas(only getting about 10 mpg city), has black smoke and carbon coming out the tailpipe.I replaced all the ignition items, pcv and fuel filter. Are these symptoms the same as what you were having?I was leaning toward the fuel pressure regulator. Also mine was showing a trouble code 45(rich mixture).

Tiny
Paulb
Aug 8, 2006.
Hi Paul. What you describe is what a mechanic friend of mine thought might be wrong with my Blazer. But mine didn't act like you're describing. You described the things my friend was saying is what he calls the " spider" tubes leading from the injector assembly to the Poppets. If your vehicle has high miles. He says that the injectors are usually the problem when gas consumption goes up and the computer shows a rich mixture. Remove the small cover on top of engine. (2 torx head screws) You will see something that looks like a small motor sticking out of the intake plenum, held on by 2 torx head screws. Remove this. It has a paddle looking thing attached to it that you will see when removed. Take a flashlight and look in the hole. You should see a few small tubes that look almost like wires. Those tubes are hard plastic and I understand, notorious for breaking. You should see fuel puddled in bottom of intake. If so. You will need to replace the lines, (dealer item), or replace the whole injector assembly which includes the tubes, poppets, injector body and fuel regulator. (About $300) If and when this happens to me, I'm replacing the assembly. Better to be safe than sorry. My friend says the intake cowl is easy to remove and the injector assembly is not hard to replace. You just have to handle it gently. Also, he says you can have someone crank the engine while looking in the hole previously mentioned and see if gas is squirting around inside. But besure to disconnect the coil wires so there is no arcing which could ignite the fuel. SAFETY FIRST! Hope this helps you.
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Tiny
Randrm
Aug 8, 2006.
Hey,
Thanks for that info.I will go and check that out.I was thinking the fuel pressure regulator, which means I would have to remove the intake manifold anyways, so I will check that first.I'll let you know what I find. Thanks again.

Tiny
Paulb
Aug 9, 2006.

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