91' S-10 blazer 4x4 4.3L I just don't get it!! Had a leak, so instead of replacing just the gaskets Iput a new manifold on right side. It runs completely different! feels like it has more power but after it warms up it starts chuggin. just about everything is new on this thing too. any ideas?

I'm gonna take a look at cap and rotor,and pick up a fuel pressure tester as well. I'm thinking it's electrical though, wire or sensor maybe

 

give your little blue/red wires for the injector a tug while shes running and see how that changes things. They go bad after years and alot of poeple have this problem.

Maybe you forgot to hook something up? O2 sensor? Are you getting SES light after warmup?

 

I've been thinking about it, I actually crossed the 2 and 4 plug wires when I put everything back together, as soon as I cranked it, I realized it and switched them back. Gonna pull the cap off in the morning. The injector wires have been replaced at some point, and I just put new injectors in it cuse one leaked. New o2 as well. I had the scope on listening for vacum leaks and I thought I heard a leak at the TPS. Is there suction there? I've got a used spare I'm gonna throw on to see if I still hear it

 

UPDATE: this is what ITS NOT- tps, coil, cap&rotor, timing, map, distributor module, computor, ESC, PCV. gonna try a new egr vacuum soleniod. It's 50 bucks and I don't know how or if it can be tested and it's all thats left.

 

So it ran OK, except for the exhaust leak, prior to changing the right (driver's side) manifold. Now it runs OK when the engine is cold and the system is bypassing the sensors but starts running poorly as it warms up.

One of the earlier posts asked about any codes being generated. Do you have any? Does your SES light work. Check there first. Some of the items you have changed would have thrown codes if they failed.

Did you check to see if the knock sensor connector is back on properly? It is really easy to knock off and hard to get back on properly. Also, depending on how the pigtail is routed it could get fried. But even then you should be getting a code. Did you change/check your timing after the installation?

 

ses works, no codes, but I've had so much unplugged and reset it's hard to say. It wasn't the solenoid I spoke of. I'm wondering if some junk might have gotten down the exhaust pipe and caused the convertor to become clogged. that would explain the sudden change after changing the manifold. What do ya think?

 

I doubt it. An easy way to test your convertor is to get under the truck and bang on it. If you hear anything rattling inside it, then you may want to get a new convertor. Its full of a honeycomb kind of stuff, and lean and rich run conditions are hard on it after a while. Depending on where you live and if you have emissions laws in place, you can just cut the cat off and put a peice of pipe in there instead.

 

I unplugged the knock sensor and started it, it runs the same unpluged. The strange thing is when it's unpluged the temp gauge doesn't work. It is between the 2&4 plugs just above the exhaust manifold right? I don't get why it kills the temp gauge. That must not be it cause the pics I'm seeing at part stores look completely different.

 

The Knock Sensor is on the Driver's side of the engine above #3 plug, under hood, driver side, lower engine area, below exhaust manifold, mounted in engine block . I believe there is also another Knock Sensor in the rear of the engine below the Distributor. The Sensor between #2 and #4 plus is the temperature gauge "sender" for your dash temperature gauge. The temperature "sensor" for your computer is in front of the engine.....

Your description of its running performance would definitely indicate a sensor problem. I went through a similar experience last year when I first got my Jimmy. It would run great when cold and then run poorly when it warmed up and the computer started using input from the sensors.

I tested all the sensor outputs (pretty easy to do) and finally replaced the Knock Sensor" and its connector. If you are not careful the pin in the center of the connection will not seat where it should and although it looks like it is OK it is not making contact. Since you replaced the manifold I would check the back of the engine to make sure that connector didn't get knocked off the Knock Sensor (no pun intended)....

 

thanks Licklog, I found it down below the oil pressure sending unit. the plug in it is real sloppy. nothing on drivers side though. I'm waiting for it to cool off and gonna put the new knock sensor on. I'll let you know if it does the trick. thanks