89 IROC 350/700--mods below

Still trying to figure out rough idle--started basically when car started running REAL rough all the time--barely made it home. Ended up taking it to a shop--they said stock Dist. was trying to destroy itself (was full of rust, etc)--replaced with a rebuilt dist, cap, rotor, coil, maf, and fuel filter. Car would run, but developed a very rough idle-- "If it was a non computer car" I would say it has a low speed miss and surging (rpm varies up and dowm 200/300 RPM) and sometimes dies while idling.

Could something in the rebuilt Dist. (like ignition module or something) be causing this?

Replaced tps and Iac (cleaned everything good) and adjusted to spec per Vader article/post- -still the same. (tps with ignition on --not running .54--it is .52 when running)

Borrowed OTC 4000E scanner and have checked what I know enough about to check--when on a road test with scanner--spk advance is floating from 28 to 31 while idling--will go to 35/36 under light accelaration, but goes back to 25/26 under hard acceleration and will stay there as long as I have my foot in it. Is this normal?

No knock by ear and by knock sensor.

What should initial timing be set at? If initial is off--can it cause a problem like this? What should total timing be at full acceleration?

 

No error codes? Does the custom PROM allow the MIL to come on?

 

i realize i'm showing my ignorance here, but I don't know what MIL is. Custom chip was in car when I bought it a few months ago and I don't really know anything about it.

I do not have a timing light, but I think I'm going to go buy one today or tomorrow.

Specific question: Going by the scanner only, it says spark advance is 28 to 32 degrees at idle (725 to 950--it is constantly varing) This seems awful high for that RPM. Shouldn't it be around 6 to 8 degrees BTDC even with the ECM kicking in to control timing?

One person I talked said he thinks the initial timing is so far advanced, that ECM is trying to control /retard timing at idle and that is why it is constantly varying, which is what is causing the rough idle and variance in idle speed, and that under light acceleration goes to max of 35, but ECM is retarding timing under full power--back to 25 to 27 degrees because it is seeing too much timing?

Until I can get my hands on a timing light, can I retard timing and use the scanner where it is showing total spk advance as a guide to at least get it better.

Would rotate dist slightly clockwise--right?

 

The ECM can't "see" timing. All it does is receive a pulse from the dist, and look up in a table to find how much later than that to send a pulse to the ignition module. However, one of the pointers it uses to find the right cell in the table, is the spark knock count; if it receives knock counts from the knock sensor, it looks in a different cell of the table to find its next-pulse delay, which will be longer (pulse occurs later, i.e. the next cyl's spark is less advanced than it otherwise would have been).

Likewise, a scanner won't tell you the actual spark timing, because it has absolutely no way to know where the piston is in its cycle. All it can tell you is how far it's moving it from whatever the static timing is set to, which it can't tell.

I'd expect to see around 20° total advance at idle, about 35° at WOT, and about 45° at cruising above 2500 RPM, viewed with a timing light and a known accurate harmonic balancer (timing mark not slipped as they often do).

 

Hmmm... I understand what you are saying. according to scanner the knock count has always been 0 when I checked it on the computer, however I have not checked that while driving.

I just went out and retarded the timing (no timing light) by moving clockwise as much as it would move (not all that much--wire plug in in dist now hitting back of intake #1 PLUG--now directly at 6 oclock position facing forward--THAT DOESN'T SEEM RIGHT!) smoothed out idle and cut down on searching both for idle and timing according to scanner. Does not surge/die now when idling at a light. "SPK advance" on scanner is still showing about 29/ 30 at idle of 775 to 825--shows 35 at light acceleration and 25 to 27 under acceleration. Am I interrpiting this information wrong. If so what is it showing?

You know, before dist was replaced, it ran REAL rough after a short 1st gear/2nd gear pass--let engine slow car mostly with some brakes--pulled up to a light --ran REAL bad for about a second then back to normal--went about 2 blocks--pulled up to a stop sign--then went to running REAL ROUGH and stayed there. (basically would not run). To me it felt like it was (or did) trying to jump time based on my old non computer hot rodding experiances. Is it possible for it to actually jump a tooth on the timing chain and then continue to run if dist is set way out of time?

How can I check to see if this has happened?

 

I just took around the block with the OTC 4000e hooked up--in one mode, knock sensor is yes or no--it shows yes when blipping throttle, but NOT under load/driving conditions. In another mode it shows a value (degrees retard --I think). It shows no value while under load/driving, but shows as much as 20/30 degrees retard when blipping throttle sitting still.

 

You need a timing light, you can't just adjust the distributor like the old days.

You need to disconnect the EST bypass line, set base timing, suggest 6-8* BTDC to start since you don't know the parameters that the "custom" chip are running off of.

The EST Bypass connector is a single wire connector, on my car it's located behind/between the pass side strut tower and fender, some are more towards the heaterbox.

Once you set the base timing, shut the car off, reconnect the EST line.

When you fire it back up, you'll probably have 16-20* BTDC with the ECM running things.

 

I agree--I do need a timimg light--I'm still trying to figure if this thing jumped time at timing chain or if maybe the mechanic who stabbed the new dist got it one tooth off and is why timing is so screwed up!

 

Your distributor has gotta be off a tooth... not a big deal as long as you have the room to turn it i guess...

also, does yoru scanner give you the advance figuers with base timing already figuered in or not?

the mere fact however its better with timing yanked out means that you were probably a tooth off on the dist. install and just running way too advanced.

 

Craig, just bring it by on Sunday and we'll take a look at it. I have a timing light. Page me on Saturday arround 4 - 5pm and we'll make plans to meet up (if it's not raining of course).

Mike (1bad91Z)

 

Mike,
Still planning on Sun--will page U Sat.

Can anybody answer a question for my own curosity "Is turning the dist cap clockwise advancing or retarding the timing?

 

ccw will advance timing

 

Hey Vader,

What is the MIL?

 

I don't know what MIL stands for, but pretty sure he's referring to the SES light.