85 4.3L TBI issue

B2Elco · Posted: Mon Mar 13, 2006 1:15 am Post subject: 85 4.3L TBI issue

Hello everyone! I have an 85 El Camino with a 4.3L V-6 that is stalling while driving. If the car is cold, it runs fine. It appears to me the Throttle Body Injector (TBI) is injecting too much fuel and the car is flooding.

A few years ago I had bought a Holly 502-8 TBI but never got around to installing it,so I figured now would be a good time. The Holley was dumping so much fuel that the car would not even start so I put the stock TBI back in.

I think there must be some sort of electronic sensor that's malfunctioning and telling the TBI to inject too much fuel. I've read the TBI section of the Haynes Repair Manual but I either missed it or it doesn't mention such a sensor.

Searching the forum I've come up with the following ideas:
1. the egr valve
2. coolant flow sensor
3. knock sensor
4. o2 sensor
5. ECM

What would be best course of action at this point? Any advice would be appreciated.

Mrapii · Posted: Mon Mar 13, 2006 1:29 am Post subject:

Why guess?, you have access to a diagnostic procedure.
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1979 El Camino\r\n1955 Chevrolet Del Ray\r\n1962 Corvette\r\n1966 Corvette Coupe

B2Elco · Posted: Mon Mar 13, 2006 8:51 pm Post subject:

I'm sorry but I'm not sure I fully understand your suggestion. If you mean I should check the OBD code, I just did and I got a code 33.

Code 33 either means Mass Air Flow sensor or Manifold Absolute Pressure sensor voltage too high.

I already checked the vacuum hoses from the MAP sensor. I will try replacing the MAP sensor, but I've read code 33 is thrown when the engine idle is unstable (which it is before it stalls).

Mrapii · Posted: Mon Mar 13, 2006 11:11 pm Post subject:

If any of the sensors were out of range you would get a hard code. The problem might be incorrect fuel pressure (easily checked) or problem that doesn't trigger a fault code such as a fuel delivery problem (very likely) or some kind of ignition problem.
_________________
1979 El Camino\r\n1955 Chevrolet Del Ray\r\n1962 Corvette\r\n1966 Corvette Coupe

B2Elco · Posted: Tue Mar 14, 2006 12:26 am Post subject:

Thanks. A GM Master Technician suggested the following before I knew about the code 33:

"It could be an o2 sensor, coolant temperature sensor, MAP sensor or TPS that has gone bad. That is what I would suggest first."

Thanks for the assistance, I now have several things to try.

I'll post my results after this coming weekend.

BTW - I had a friend of mine check the fuel pressure and it was correct.

johncgg · Posted: Sat Mar 18, 2006 7:00 pm Post subject:

B2Elco · Posted: Mon Mar 20, 2006 9:54 am Post subject:

OK, it was not the best use of my Saturday Sad

After checking the reference voltage to the MAP sensor and the voltage when connected, i concluded that was the problem. I replaced the MAP sensor and then the car wouldn't start at all. I cleared the OBD memory and then tried to start is again...this time I got code 22 (throttle position sensor), so I thought I fixed one problem only to discover another.

Since the throttle position sensor is part of the TBI, I reinstalled the Holly 502-8 TBI I have. The car still won't start and now I'm getting code 33 again! $%*#!@

johncgg - were you getting OBD code 13 when your o2 sensor was bad?

johncgg · Posted: Mon Mar 20, 2006 11:40 am Post subject:

B2Elco · Posted: Wed Mar 22, 2006 12:08 am Post subject:

I got it!

I double checked all my connections and the new MAP sensor connector wasn't all the way in Embarassed

. It must have happened after I installed the Holley which explains why the code 33 came back.

So bottom line, I had two issues with my car: 1) bad MAP sensor, 2) bad throttle position sensor.

Not only is it now running, I got the Holly TBI installed/working and it's finally idling at the correct RPMs. Since I bought the car in 1999, it's been idling too high. All I have left to do now is adjust the timing.

I have one more question: while checking all my vacuum lines, I noticed my EGR control solenoid floating behind the TBI...where it it supposed to be attached? It has two vacuum lines on top and (what looks like) one at the bottom in the center of a clip...but the one at the bottom isn't connected to anything.

johncgg · Posted: Fri Mar 24, 2006 8:54 am Post subject: EGR

B2Elco · Posted: Mon Mar 27, 2006 10:10 am Post subject:

Update: now I'm getting a CEL when the car is cold. I checked the OBD and I get a code 32 (EGR closed at engine start-up). I guess I need to figure out where that EGR control solenoid is supposed to be connected.

My engine is also stumbling when I try to accelerate hard (oxygen sensor?).