Engine Surging 95 4.3

[Sredsobad]

I have a 95 "W" 4.3 S-10 and I notice a power/engine surge during acceleration and steady engine speeds from stop to around 2500-3000 rpm ranges. I have just completed a full tune-up including both O2 sensors, cap, rotor, plugs, wires, trans filter and fluid, fuel filter. Fuel pressure is steady at 58psi while driving. I removed the intake plenum to inspect the fuel system (no defects noted) and cleaned it out fully while i had it off. I replaced the TPS because it was causing erratic indications on the scope and a noticeable hesitation during initial depressing of the gass pedal. However i did notice that while watching the O2 sensors commence their crosscounts, the engine surged along with it speeding up as the sensor went rich and then came down as the sensor went lean. It would happen at any engine speed other than idle up to the 3000 rpm range in neutral. I know that the sensors are supposed to act like this, but I also know that it's not supposed to make the engine surge. Im thinking an injector might be dumping too much fuel into one cyl as the mixture goes rich, but i cant tell from the look of the plugs as they all have the same appearance. One thing i didnt really pay attention to is the time it takes for the sensors to do their switching.... Any suggestions or help with this matter would be greatly appreciated. Mahalo!!

[ericn1300]

sounds more like the O2 sensors are reacting to a rich condition rather than the other way around, i'd check the EGR, PCV and for a vacumm leak since the surging is at low rpm. if you acess to an emission tester you might want to sniff around for a crack in the exhaust manifolds, though thats unlikely.

[J-Mech]

I cant' remember, does a 95 have a MAF sensor. If it does, might try cleaning it.

[frehol]

Originally Posted by J-Mech

I cant' remember, does a 95 have a MAF sensor. If it does, might try cleaning it.

No, there is no MAF on 95´s

//F

[Sredsobad]

yeah, no MAF...MAP instead...and made sure there was nothing obstructing it. i have checked the pcvs and im pretty sure there's no vacuum leak because it idles great. it only happens when im pushing the gas pedal. i haven't checked the egr though. its my next step i guess. Alohaz

[94 Jimmy]

Does the 95 have a Spider, CPI, Central Port Injector, call it different things, spells trouble. While you had the intake apart did you note if one side was clean the other side dirty with carbon. On my 94 the injector rail is inside the upper plenum of the intake and the fuel regulator tends to leak. The drops of gas wash the inside of the maniford where they hit, they also cause one bank of cylinders to run rich the O2 sensor compensates and drives the other bank lean, not a good thing.
I have also experienced the same thing when a chunk of carbon got into the EGR valve and held it open, also not a good thing.
They made a lot of changes in the 95 over the 94, OBDII is the big one. But search the forum for CPI and EGR and you'll find some help.
Good Luck
94

[94 Jimmy]

Does the 95 have a Spider, CPI, Central Port Injector, call different things spells trouble. While you had the intake apart did you note of one side was clean the other side dirty with carbon. On my 94 the injector rail is inside the upper plenum of the intake and the fuel regulator tends to leak. The drops of gas wash the inside of the maniford where they hit, they also cause one bank of cylinders to run rich the O2 senson compensates and drives the other bank lean, not a good thing.
I have also experienced the same thing when a chunk of carbon got into the EGR valve and held it open, also not a good thing.
They made a lot of changes in the 95 over the 94, OBDII is the big one. But search the forum for CPI and EGR and you'll find some help.
Good Luck
94

[Sredsobad]

Thanks for the tips everyone! when i took the plenum apart, the whole thing was dirty...both sides. so i know the fuel lines and regulator aren't leaking. i hvent really had alot of time lately to ring it out, but im leaning towards the egr being the culprit. i did notice a lot of carbon in the egr hole on the plenum....so, im gonna try clean it up one day and post the results.

Aloha!