I am in the process of rebuilding another 88 coupe. The engine is a 383 with a superram. It recieved the car and engine in boxes. It is all together now and I have been having idle problems. It is never the same or steady. I have been all over looking for vacume leaks as well as going over the TPS and IAC. Nothing helps so I reset the base timing with the EST disconnected(6*). While doing this I noticed the idle was perfectly steady. As soon as I plugged the EST back in and restarted it, it was back to the same up and down as well as stalling just after start up unless I flutter the throttle. With the EST plugged in I see 49* timing at 3500 rpm and it is all over the place at idle. With the EST disconnected and base timing at 8* it will advance to 24* by 2500 rpm. While driving at this setting it runs great until about 3600 rpm then it runs out of timing. Is this correct or do I have an incorrect/faulty dist?

sorry for the long post but I am sure I have still left something out.

 

"seeing 49*@3500" are you using timing tape or a scanner or? (sounds like a lot to me)
In general it sounds like this car needs to be tuned, or sending additional data to whoever tuned it to begin with.

 

First, there is no mechanical or centrifugal advance in this distributor. The 24° at 2500 rpms with the EST plugged in sounds about right. However the amount of advance varies based upon whether the engine is being held in neutral at a fast idle or if it is in gear, accelerating. The ECM changes the timing based on engine speed, and load, as determined by readings from the TPS, MAF (or MAP), just as the old mechanical advance distributors did back in the day. Because of the electronics involved, it isn't possible to check the mechanical and vacuum advance mechanisms or even "total timing", independently, as we once could.

What is your timing at idle, just after you plug the in the EST with 6° base timing? I think anywhere from 16° to 22° is about right. With no load on the engine, 49° at 3500 rpms (the combination of the equivalent of both centrifugal and vacuum advance), may not be out of line. Your most significant symptom is the idle going to pot as soon as you connect the EST. I think the very first thing you ought to do is to verify the TDC mark on your damper. If the ring has slipped, all of your timing readings are meaningless.

RACE ON!!!

 

It has a brand new Fluid Damper balancer on it and the TDC was verified as well as the cam being degreed prior to installing the engine. The timing will advance with the EST disconnected. I set the base at 8* with the EST disconnected then run the RPMs up to 2500 and I am reading 24*. So it is advancing 16* with the EST unplugged. I have almost 30* as soon as I plug the EST back in at idle in park. Then I will turn it off and restart the engine and the timing is jumping from 17* to 35* at idle in park. I am using a Snap-on dial back light to get the readings. I just had my light checked out and it is accurate to +/- .2 degrees.

Would it be possible to just install a good old style Mechanical Adv. distributor/ignition box and allow the ECM to only control the fueling without tripping a SES light?

Also I have a cable from ALDLcables.com just I cant figure out how to use the scan software(tunerpro and winALDL).


Thanks!!!

 

Not without jumping through a lot of hoops. The ECM powers up the fuel pump relay when it detects pulses from the distributor. The ECM senses the engine rpms and it pulses the fuel injectors based on pulses from the distributor, for starters.

I don't think hooking up those cables and using that software is going to tell you anything that your timing light hasn't. Some ECM/computer geeks may prove me wrong on that. Obviously your advance mechanism is fungoo. You can study your FSM to see if it touches on a problem like this. I have never had, seen, or heard, of problems like this, so I haven't looked. Concentrate on EST system trouble shooting. You could remove the distributor and do all the checks on it. Maybe you'll find a loose wire or a bad connection. You can always have the module checked at one of the auto parts stores. You've got yourself a good one.

RACE ON!!!

 

THANKS!!! So the dist. shouldnt advance at all with the EST disconnected? I have a stock dist from a SS454 that I think I am going to try it appears to be the same as the one on my other 88.

I am not SURE that this is the correct dist for this car. Like I said it all came in boxes and I did find some really stupid stuff.

 

Yes it should. There is advance built into the module. What bothers me is the jump from 8° to 30° just by plugging in the EST. It should be in the 16° to 22° range as I said earlier. I have never documented nor have I seen where anyone else has documented the module advance. I just know it happens. There is no doubt in my mind, however, that 30° is too much advance for an idle speed under no load. That is one reason I suggested inspecting the distributor. There may be a short, a loose wire, heck maybe even the pick up coil is bouncing around in there. If that SS 454 is an EFI engine, that distributor ought to be a good sub.

RACE ON!!!

 

just to end this thread...I did find a couple of bare wires from the module to the cap. How they got that way I have NO IDEA! Its all good these days, Thanks for all the help.

 

Thanks for the follow up. Too often we never hear if a problem was solved or if so, what was the solution. It is nice to know that I wasn't totally out to lunch.

RACE ON!!!