1995 Chevy S-10 4.3 W motor losing power

[rrabat]

I have a 95 S-10 with the 4.3 W motor, 74,000 miles and auto trans. The truck seems to lose power. The engine has a small vibration on acceleration. On medium to hard accel. the engine will lose power. I have had three ASE mechs and one backyard mech look and drive the truck but can't put their finger on the problem. I have driven the truck with an OBDII scanner hooked up but haven't been able to solve the problem. The loss of power is much more noticable when the weather is warmer than colder. I don't believe that humidity has anything to do with it. The engine will loose power for a few seconds then surge. You can hear the change and see the change on the tach. The cpi has been changed twice at $314 a pop. The fuel pump and filter have been changed Three times. The two O2 sensors have been changed due to check engine lite (heater), The tps and iac have been changed along with plugs, wires, cap and rotor. The map sensor has been check for a smooth voltage change as vacuum in the intake changes. A compression check has been done and the range is 165 to 170 psi. The spark plugs have a nice white burn to them. The truck starts fine and idles pretty smoothly for 74,000 miles. It may have a slight shake every now and again at idle. I would think that is do to the ecm leaning the vehicle out. I may tackle an intake manifold gasket for my next move. I'm thinking now that I may have a small vacuum leak at the manifold. If anybody has any ideas before I tear into the top of the engine it would be appreciated. I am waiting for the factory service manuals to be mailed to me. Thanks for all your help and input.

[cobra1]

does it come up to full operating temperature? also, have you checked the IAT (intake air temp sensor). as for vacuum leaks, if you have one, it would really effect the idle. if you wanna check, CAREFULLY spray a little WD-40 in suspected areas, the engine speed will increase if there is a leak. just dont spray it on a hot engine or hot parts, the stuff is flammable.

beyond that, id be looking at the computer, given all the other items that have been changed.

sorry to hear yours has given you such trouble. i have a 95 extended cab 4.3 w/CPI that has 176,700 miles on it. still has original CPI unit.

only things ive done are... replace crank sensor, a/c pressure switch, oil cooler lines, and alternator. along with the normal maint stuff, brakes plug, plug wires, etc.

[VJL]

Under the black plastic "Vortec" beauty cover on the CPI there is a butterfly valve sensor (looks like a round plastic disc about 3/4" thick) that flips-flops under heavy throttle, forget the exacts about it and I don't have my books with me but I think it tells the PCM that more coal is needed for the fire. I think the airflow inside the CPI is a variable path or something... Kinda Audi-ish.

[rrabat]

The engine does come up to operating temp. I'm going to look at the intake air temp and the valve. I have had the valve out and it turns freely. Thanks once again for the input. I am still waiting for my shop manuals to arrive.

[thomp22]

1994 S-10 Blazer 4.3l (w) auto. Rebuilt @ 160,000 now 195,000 mi. I am having the same issues as yours. If you find anything that fixes the problem, please let me know. I have checked almost all the things, and replaced alot of the parts you mentioned. Still I have this little vibration very noticable when the trans shifts from 1st to 2nd. Actually looking at almost anything someone suggests, I am lost. Just letting you know your not the only one out there with the problem. So it has to be something that makes the vehicles act this way?

Tim

[rrzimmer]

Originally Posted by thomp22

1994 S-10 Blazer 4.3l (w) auto. Rebuilt @ 160,000 now 195,000 mi. I am having the same issues as yours. If you find anything that fixes the problem, please let me know. I have checked almost all the things, and replaced alot of the parts you mentioned. Still I have this little vibration very noticable when the trans shifts from 1st to 2nd. Actually looking at almost anything someone suggests, I am lost. Just letting you know your not the only one out there with the problem. So it has to be something that makes the vehicles act this way?

Tim

Here something to try. Plug in a scanner and see if the knox sensor is activating the timing to be retar. The vibration you said you have will cause the knox sensor Spark Control Sensor to activate. You may have a harmonic balancer going out which might be your vibration. I would realy try and take care of your vibration first.

[JMorales]

Have you replaced your catalytic converter? I had a problem with the loss of power and it was a plugged converter. They say you need to replace them ever 70,000 miles or so. I couldn't believe the change in performance since. I had everything checked before I changed my exhaust system, and everything was normal. It even passed smog with flying colors even though it was plugged.

J

[rlith]

The cat is a good place to start as Jmorales says... But also pull and clean your EGR and the EGR port on the manifold side... If that gets clogged you will get the same symptoms... Pull your upper plenum and check for signs of washing. If the passenger side is washed your CPI is leaking, if the driver's side is washed, you have a bad nut kit. Also check the pressure at the shrader valve. It should be at 56-60 to start and 61-64 at running.