Hi all,

First post here, trying to help a friend fix his Blazer, thanks for having such a great forum. I have worked on 2.2l's, 2.3l's, 2.4l's and a little bit of 2.8l V6, but this is my first go at the 4.3l. I did a little searching here on the site and elsewhere but didnt come up with any solid answers to my problem.

1994 Chevrolet Blazer 4.3l Tahoe 4x4:

Has rough idle, and stumbles/misses during acceleration. Have replaced plugs, wires, cap and rotor since problem started.

Has code 22(TPS), 32(EGR), and 34(MAF) showing.

I pulled the top section of the intake manifold off to get a look at the fuel injection system, it wasnt dry in there, but wasnt very wet either, there was a very small amount puddling of what smelt like fuel however. I turned the key to pressurize the system and didnt see any obvious leaks. The "overflow" or "bypass" hole of the fuel pressure regulator was slightly wet, it did not drip during the short time I had the system under pressure, only when I touched it was there noticably fuel coming from/behind that hole. The planum/intake manifold gasket was not in the best of shape, and may not have been fully sealing between the intake runners, I believe the exterior of the plenum was sealed though.

Its my guess that the fuel injection system is working ok, but that one of the sensors went bad, but it could be the oppisite.

I have a new gasket for the intake plenum, butam not sure if I should replace the fuel regulator/injector unit or put the upper part of the plenum on and start replacing the sensors indicated by the codes.

Any help greatly appreciated.

 

where you able to check the fuel pressure to ensure the fuel pump is pumping enough fuel ? How many miles are on it ? did you replace or check the fuel filter ? I had a Chevy Full Size Van do the same thing once I changed the fuel filter it ran like it did when we first got it with 30,000 miles on it, I tried blowing through the fuel filter when I removed it and I couldnt even blow enough air through it to feel it on the other side [&o].

Another thought I just had is you could have a plugged catalatic converter or a stuck EGR valve but those guys arent cheap, I had a stuck EGR and a plugged cat when I put my supercharger on my 98 S-Dime and it would barley even run enough to drive it to the exhasut shop (Missing and running like complete crap I had it WFO most of the time to maintain 45 MPH) were I had a 3" single exhaust ran with a dyno flow muffler and a high flow cat that fixed the problem but I know once the internals brake loose in the catalatic converters they can sometimes turn inside the cat and restrict the exhaust alot.

Just some thoughts good luck and let us know what you find

 

Have not checked the fuel pressure or filter. Owner tells me he had new fuel pump and filter put on "a couple years ago". Has 114k on it now.

It could be the EGR because I am getting code 32, the owner has given me the go ahead to spend whatever is needed to replace parts, I am just not sure where would be wisest to start.

 

Two things to do first - clean the EGR valve and clean the MAF sensor. Check back with the results.

 

There is no MAF sensor on a 94. Only a MAP sensor... Which is what makes this kind of confusing...

You can test the TPS sensor by making sure that it has +5V with the key on, a good ground, and then monitor the sensor return to the PCM with a DVM to make sure that it has a smooth transition from around 0.5V at closed throttle to around 4.5V at wide open throttle.

With no vacuum pressure in the plenum, I would expect you to find little actual leakage on a marginal FPR. If any wetness was present, the FPR is leaking, so no, things are not all right with your fuel system.

 

There is another sensor in the 4.3l intake, my Beretta 2.2l had the same one, but the 2.3 and 2.4 motors do not, dont recall if the 2.8l V6 did. Not sure what its called then, but it was very dirty... its small and sticks into the intake just before the throttle body.

Not sure if youve ever seen the inside of the 4.3l plenum or not Swartlkk, but it appears to me that there is passages that lead into the center area of the plenum if so there would be vacuum present.

Cleaned outEGR last night, picking up gasket this morning. Will be testing TPS as well today.

If I put everything back together and still dont have a normal running condition after cleaning egr and testing/replacing TPS should I go ahead and start on the fuel reg./injector unit? Should I replace it all or just the regulator side?(if Im understanding the way the parts are available) or would replacing one of the sensors be a better place to start?

Thanks for all the help so far!

 

Man, I am not sure if I can remember what the CPI motor looks like...[:-] Stick around a bit and you may find how silly that question really was.

As far as sensors/valves on the intake of the CPI motor, you have: [ul][*]MAP sensor - manifold absolute pressure - located behind and slightly to the right of the throttle body when looking at the engine from the front - it is a rectangular plastic part that is held on by two torx screws. The electrical connection points down towards the engine.[*]MTV - manifold tuning valve - located on top under the "Vortec" cover - it is a round plastic housing held on by two screws which I believe are T20.[*]IAC valve - idle air control - located to the left of the throttle body. It has a round metal housing held on by two torx screws with the electrical connection pointing back towards the firewall[*]TPS sensor - throttle position - located on the right side of the throttle body, again held on by two screws. THe electrical connection is pointing towards the front of the vehicle.[*]IAT sensor - intake air temperature - should be in the black plastic intake duct between the throttle body and the filter box. (sometimes referred to as the ACT sensor - air charge temperature)[/ul]As far as where to go after you test the TPS and clean the EGR, I would start with a fuel pressure test to verify that pressure is bleeding off when the key is turned off. That is a tell-tale of a leaking FPR.

 

Ahh.. its the IAT.. it was very dirty, clean now though.

How long do you wait to see if fuel pressure is dropping? I know pressure will drop over time, the system wont hold pressure overnight for example [8D].. but was just curious on how long.. might pick up a pressure tester today if I can get one on loan.

I am thinking of just going and getting a pressure tester,regulator kit and new egr gasket and throwing it back together and seeing how it runs from there. At least at that point(if fuel pressure is high enough i.e. injector is good)I can get the plenum put back together and get out of there.

TPS tested good.

 

System pressure should hold at some point. Typically, in my experience, it will drop a few psi, then hold steady. I have come back to a vehicle, with a properly functioning fuel system, after it has sat overnight and see the pressure still at 50psi.

If you can get the FPR off without disturbing the nut kit (internal lines on the driver side in the plenum), then you can get away without changing them, but if you have to move the spider, even a bit, you are much more likely to have a leak at those internal lines after the other repair is completed. Just something to think about.

Lindertech.com has a CPI FPR update kit which will upgrade the CPI to the same FPR that is used on the SCFI motors. This design is much more "fail-safe" than the standard one which means that it will typically fail internally, bypassing fuel to the tank instead of leaking into the intake.

 

You can do it without disturbing the nut kit at all. The 2 torx security screws are easy to get to from the passenger fender - it's a straight shot. My spider & nut kit didn't even twitch when I replaced mine.



If you have a Harbor Freight near you, their Fuel Injection Pressure Test kit is $12.