Trying to track down a intermittent miss at idle I've had for a few months. A little history on the car. It's a 1987 Trans Am with the 5.7 TPI engine. I've replaced the coil, plugs and wires, new distributor from Autozone. Bosch 3 injectors. Nothing seems to remedy this miss unless I unplug the EST. When I do that it's smooth as day. With it plugged in I get a intermittent miss cold or hot and at idle and very low throttle. Also get the popping through the exhaust on deceleration. I don't have any SES codes either.

 

I had those exact symptoms on an 1986 LG4. Fixed with an ECM swap.

 

Funny you mention that because The EGR hasn't been working and has been capped for as long as I can remember but it's not throwing any codes for it. Same for the EGR solenoid. It'll easy throw a code for the EST or MAF.

 

Had the same issue & fix on my '91 GTA.

 

I ordered a ALDL cable to start some data logging. Will search the JY for some ECMs. According to this page provided by this site https://www.thirdgen.org/ecminterchange, any of these ECMs will work i'd just have to use my PROM? I have the 165 ECM

 

For a quality ECM that you know would work, I would highly recommend hitting up TunedPerformance on this site. I got a replacement one from him for $50 and I know it would work.

 

I uploaded a video so you guys could get a better idea of the miss. I drove around with the EST unplugged for a few days taking it easy. Plugged it back in tonight. Another key issue I've been having is bad pinging at WOT. Have tried different grades of gas from different shades of gas stations. Didn't help a thing.

http://www.youtube.com/watch?v=0_WDk...ature=youtu.be

 

I played with the timing with the EST connected and the miss is nearly gone. Nothing like what it was.

 

Tried a different ECM and ESC. Still the same problem with EST connected. Only thing I haven't done at this point is the knock sensor. Any suggestions here?

 

Unplugged the knock sensor and still same thing. Nobody has any pointers for me at all?

 

Is the timing set to spec? Balancers have been known to slip.
See if the miss is at a certain cylinder.
Check ecm grounds.

 

Timing is one thing still in question. I put the timing light on it with #1 and can't see the timing mark on the balancer in relation to the tab. If I put it on #3 or 5 it comes into view but is way advanced and off the timing tab. The correct balancer is on there and is about 10 months old. Why can't I see number 1 cylinder ?

Checked all grounds and were good.

 

Put #1 up on TDC compression stroke & then check the mark, I know its hard on a sbc, I use a piece of a coat hanger & feel the piston as it comes up.

 

I did this earlier today. Used some single automotive wire. Had my fiance put her finger over the hole until she felt air and I heard it as well. Rotor was pointing dead at number 1 cylinder, but the timing mark on the balancer was at the 9 o'clock position.

 

If your sure the balancer hasn't slipped then make your own mark.

 

Just wanted to update you guys on this. My balancer had in fact slipped nearly 180 degrees from the keyway. Not only that, it slid back towards the timing cover. So replaced that. But my main issue with the EST was the distributor. Bought it about 12 days ago from AutoZone so go figure. I appreciate all the help. This is a awesome community.

 

This miss came back not long after but chalked it up to something in the engine.
2 years and a new engine, it's still there! Without making this long I have a video of how it is now and a short list of what I've done since swapping a new engine in a few weeks ago.

Fuel filter
Injectors
Another brand new distributor
Swapped ECM and PROM
Replaced MAF
O2 sensor
Swapped ign coil for known working one

Here's video

 

Do you live on top of an old Indian graveyard?

 

Haha. Starting to think I have a ghost playing with some wires somewhere.

 

Whats common between the 2 engines?
I.e what else did you reuse with relation to ignition?

 

As far as ignition I reused the complete distributor, ignition coil. Have been through a few sets of spark plug wires over the 2 years. New engine has new plugs specifically for the Vortec heads since they need a longer reach into the combustion chamber.

I guess it's worth mentioning I put in a brand new complete distributor yesterday, the miss was still there but it wasn't as profound like in the video.

 

Is the miss limited to 1 cyl?
I.e if you short cables to ground 1 at a time, can you find one where the miss nothing changes?
If you short a 'good' cyl, you'll know.

 

Isolated that as well. With a timing light anyway, went around all the wires. They all produced the same light pattern.

 

I'm very sorry to resurrect a 9 year old thread. Did you ever figure what the issue was? I have the exact same issue you did.