Miss/stumble on carbed 3.8 (was: Do you know why?)

[slyfox]

Ok the 82 Old's 3.8 mild cam and intake off a 4.1 and a computer controlled carb, You guy may know I got it running and it ran pretty good but still need to get a scan tool to check it out with but my only complaint was the idle was a little slow and it has no stored codes yet oh and about 150-200 miles on it.

Now it developed a miss on a pull (up hills etc.) but not at cruse or idle also noticed radio noise not there before so I thought wires. Changed wires, plugs, cap and rotor no change. Now I for whatever reason unplugged the 4 wire connector to the distributor and runs fine and NO RADIO NOISE. I understand that the settings on something may be wrong causing the miss in closed loop but why would this effect the noise in radio? I know some how they are connected I just can't figure it out.

As a side note this car is the wifes she does not go far, just to take the boy to school and pick up grocerys do you think it would hurt to run it for a few days that way till I can check it out better, hard to get much done after work.

Thanks guy for any help you can give.

[Keller]

The 4 wire connector is the EST connector. The ECM controlled timing is not happy under load. Should be OK to drive disconnected.

Is there a regular HEI module in the distributor, or a "high performance" one? The latter often have extra timing wired in.

[slyfox]

Right with the 4 wire connector unplugged the ECM cannot adjust timing and it stays in open loop, but could the control mod in dist. cause it to arc somewhere (causing miss fire and noise).

[Keller]

You didn't answer my question:

Originally Posted by Keller

Is there a regular HEI module in the distributor, or a "high performance" one? The latter often have extra timing wired in.

Since it only happens when the motor is stressed, I believe it may be a case of too much timing (which might be due to an aftermarket "high-performance" ignition module that causes too much timing), perhaps the timing is not sent properly, or the cam is still not installed completely right.

Too much timing will quickly cause detonation, or "ping" when the motor is under load. As it might on a uphill climb. In addition, too little fuel will do the same.

Remember: The computer was not adjusted for any changes in your motor. While it has minimal control of the fuel via the carburetor, it has a lot of control of the timing.

So:
- Was the cam installed "straight up" or advanced?
- Is the ignition module OEM GM, aftermarket, or "high-performance" aftermarket?

[slyfox]

Should read a little closer, no the HEI is all stock I been told that unless I am going full race it is a waste the stock stuff works fine. Oh and the cam after pulling the front of motor back apart it was set to the stock setting. The motor could be getting to much advance with the computer however I have no heard and pings. ( have to keep looking back at your post I don't always remember all you wrote)

[Keller]

Originally Posted by slyfox

I been told that unless I am going full race it is a waste the stock stuff works fine.

Very true. Even "race" cars may not need the more aggressive modules.

And most cars with HEI go their grave with a perfectly fine module in them. They are very reliable. I worked with one of the forum members to adapt a used junkyard module to a non-HEI unit in order to make it work with an Accel throttle body EFI system.

Just because you do not hear detonation does not mean that it is not occurring. Did compression change at all?

My next suggestion would be to either (1) try a tank of premium vs. regular next tank and see if it makes a difference and/or (2) disconnect the knock sensor as a test. One or both of these may allow the car to run better connected. However, disconnecting the knock sensor may make the ECM throw a code. Try some higher octane gas first if you are sure you have the timing set correctly.

[slyfox]

Thanks but I don't have a knock sensor, I kinda wish I did and it just so happens that there is high test (93 octane if you consider that high) because the old motor would not run on anything but, would ping like h@# on anything lower I think it was the little tit in the middle of the stock pistons I think was use in assembly that stuck up about 1/2 inch and was threaded but that is another story.

I was looking through my stuff and I have a used mod in the shed I think I will give a try and see what happens. Even if I go buy a new one its not to bad 25 bucks it would not be bad to have a good spare around.

But please if you got anymore ideas lets have them. For 2 cents I would go get an early model dist. and a Holley and put this all to rest.

[Keller]

Originally Posted by slyfox

the old motor would not run on anything but, would ping like h@# on anything lower

Must be a reason. Have you checked your EGR operation and are you sure that the passage isn't caked shut with carbon?

[charlief1]

Your timing should be adjusted to 15 degrees at idle with EST disconnected. You're experiencing "lean knock" from the carb. It was very common on the E4ME if everything wasn't adjusted right. You can take the primary plunger adjustment plug out and turn it 1/2 turn counter clockwise and it should help some, but get the initial timing set right first.

[slyfox]

Ok Guys, the OLD motor pinged badly all the time and I had to run 93 octane all the time and I also disconnected the EGR and the exhaust flap a long time ago to keep it running good for what it was.

Now the new motor EGR is there but no vacuum going to it. I tried it and it runs like crap the air pump is not on there either (hole plugged in manifold). The missing went away after messing with the TPS a little more it is now set at .67 volts, the base timing is set at 15 degrees with the 4 wire plug disconnected.

As of right now it runs well smooth through rpm range and the only complaint I have right now is it idles a bit slow for me but it does not stall (500rpms). I have no codes other than the one for the 4 wire plug being unplugged oh and the noise in the radio when away after changing the ignition mod.

I now need to get a scan tool or get someone that knows these carbs work with it a bit.

Thanks for the help and if you got more info let me have it I am more than happy to learn as much as I can about these motors.

Oh charlief1 counter clock wise on the primary plunger will richen the mixture?