OMG ! I couldn't believe its the ignition coil !

[AC439]

I think I should post this just in case anyone else has similar problem and cannot find solution.

Problem - Engine vibrates at around 2000 rpm under some load (such as 4th gear @ 40 mph). Any rpm below or above, engine is smooth.

I did post here and researched on internet and got some insights - bad engine mount, leaking head gasket, fuel pressure problem, drive shaft worn out etc. Basically, its everybody's guess and theirs are as good as mine.

I knew my head gasket was not done correctly before and I did use Bars head gasket repair and it runs ok after using it. So, I decide to do my head gasket again during thanks giving. After 10+ days of on/off working on the HG, I re-assembled everything and the car runs better and the peppy-ness has come back. However, the 2000 rpm vibration is still there but less pronounce.

I was like what the heck causing this ? I further google but used different search criteria like "misfire with low rpm" and it came up with very different insight - ignition coil !!!

There was a case that a guy tried very hard to reproduce the issue until there is a CEL code which points to a certain cylinder (he got a V8) misfire and he changed out the COP (coil on plug) and everything is fine.

Few years back I put a aftermarket coil (similar to Accel but a generic no name coil) and changed it back to original factory coil (as old as the car). So I was like it wouldn't hurt to put it back to see. I have really troubleshooted for a long time to no avail and pretty much everything was checked.

After put back the aftermarket coil, I do not feel the vibration anymore. Car is very smooth now. I have a new set of NGK wires and NGK G-power plugs with original dizzy (rebuilt) and now couldn't be more happier.

I think the original coil is getting weaker (32 years old). Hope this helps someone with similar problem.

[Dr_Snooz]

Glad you finally got it figured out! I changed my coil out about 7 years ago. I had a bad feeling about it, not sure why, but my smog numbers were creeping up into bad territory and I had a miss at idle. I bench tested it and it failed, so I swapped it.

[AC439]

Which coil do you use ? Accel 8140 ?

I am using a generic canister type coil but thinking changing to Accel. Advance auto still sells them for $32 list, probably can get one for $27 with their 20% off coupon.....

I drove the car 4-5 times after putting the coil on. There is still little misfire-like vibration at around 2k under load but the symptom has been reduced by 75% compare to stock coil. It is not as noticeable as before but still there. Now I know its ignition related to the very least. I went to advance and grab a set of NGK v-power just for the heck of problem isolation since most people here us v-power. Got it install this morning and do not feel any difference compared to the g-power. I am going to keep using the v-power for a while to see.

I went back to the FSM and read the dizzy section. I did not check and make equal the reluctor gap so I'm not sure if this plays a part in the problem. If the reluctor is not giving a clean trigger to the power module to drive the primary winding of the ignition coil, I may have a problem getting the necessary secondary voltage (just my theory). So will take out the dizzy again and check and adjust the reluctor gap...

[InAccordance]

Have somewhat of a similar thing going on with mine but it's at 4k. Right as I hit 4k on the dot, the tach bounces once or twice and it has a misfire. Once you're past 4k, perfectly fine all the way to redline and beyond. Not too worried about it at this point and attribute it to old distributor and coil but I'm getting rid of those in a few months so it just needs to last that long.

[Dr_Snooz]

I'm just using a stock coil replacement. Can't even remember where I got it. I also have a relatively new Ignition Control Module and a half-baked set of wires made of an old set of wires selectively replaced with even older wires after the field mice ate a few for me. :facepalm:

I'd say go through your ignition components carefully and inspect them. I would run every FSM test possible for the dizzie, ICM, coil, etc. Replace anything that isn't optimal. Also be looking for outlier stuff like a dizzie shaft that feels sloppy or crunchy, resistance readings that aren't smooth but hop around, etc. These cars are getting to the age where it might be worth just replacing entire systems when they start to act up. New dizzie, coil, cap, rotor, even the wiring coming from the battery. It gets to a certain age and then starts failing in weird ways that you can't figure out. Just pull it all and replace it with new stuff. Replace it with new OE stuff if possible, or as close to it as you can get. You need to do that if you're going to keep it running well for the long haul. Otherwise it becomes a constant headache that you're always farting around with and it brings you down.

The tach hop is almost certainly an ignition module going bad.

[InAccordance]

Snooz, PM me your address and I'll mail you a brand new set of plug wires, no charge. Have like 7 sets left lol

Like I said though, only need it to last a few more months then I'm getting the rest of the stuff for the Megajolt conversion so unless something breaks to where it wont run, not even going to bother.

The module is that thin silver box with the 4 pins thats stuck to the side of the distributor right? If it is, I have one from an FI car if it'll work just the same.

[Oldblueaccord]

Ill write this up later ....but the box stock EFI, Standard Auto Parts coil the specs as new are way way off. I have contacted them.. usual interesting story.....:lol::lol::lol::rofl::rofl::blah::blah:

I dont think this will cause ICU damage but it could. The total resistance was way way low.

[AC439]

I have a new dizzy that I bought few months ago and there is no difference from the original dizzy except the ignition timing was off due to non calibrate vacuum advance (have posted in another thread about it). So I am using the original dizzy. Only thing I didn't check is the reluctor air gap on OEM dizzy.....In this case, I am pretty sure most components related to the dizzy are good.

Seriously, after I replace the OEM coil with the canister generic coil, the first 10-15 mins test drive felt no misfire. As I have driven the car more, the misfire seems to have come back more for some reason. It almost feel like the ECU somehow drifted off to the way it was based on newly learned data and adjusted its own data map. Also when car is cold (like the first 30-60 seconds), misfire is less and as car warmed up, the misfire is more pronounce. This leads me to suspect the O2 sensor due to closed loop operation when warmed.

Anyway, I took the car on interstate today. Other then the little misfire at 2k rpm, the car has regained a lot of power. The interstate cruising is very smooth. Even at 60mph, I could easily get the pull to 75mph to pass a bimmer without problems. Also seems like mpg is better. I think I'm closing in to the problem but not quite there yet.

Next 3 things on my todo list :
- check and adjust reluctor air gap
- replace fuel pressure regulator (ordering one)
- replace O2 sensor

[Dr_Snooz]

Snooz, PM me your address and I'll mail you a brand new set of plug wires, no charge. Have like 7 sets left lol

The module is that thin silver box with the 4 pins thats stuck to the side of the distributor right? If it is, I have one from an FI car if it'll work just the same.

PM sent! Woohoo!!!

Yeah, the ICM is the silver block on the side of the dizzy. I wouldn't count on your swap working, but you can give it a shot. Megajolt is a superior solution.




I have a new dizzy that I bought few months ago and there is no difference from the original dizzy except the ignition timing was off due to non calibrate vacuum advance (have posted in another thread about it). So I am using the original dizzy. Only thing I didn't check is the reluctor air gap on OEM dizzy.....In this case, I am pretty sure most components related to the dizzy are good.

Seriously, after I replace the OEM coil with the canister generic coil, the first 10-15 mins test drive felt no misfire. As I have driven the car more, the misfire seems to have come back more for some reason. It almost feel like the ECU somehow drifted off to the way it was based on newly learned data and adjusted its own data map. Also when car is cold (like the first 30-60 seconds), misfire is less and as car warmed up, the misfire is more pronounce. This leads me to suspect the O2 sensor due to closed loop operation when warmed.

Anyway, I took the car on interstate today. Other then the little misfire at 2k rpm, the car has regained a lot of power. The interstate cruising is very smooth. Even at 60mph, I could easily get the pull to 75mph to pass a bimmer without problems. Also seems like mpg is better. I think I'm closing in to the problem but not quite there yet.

Next 3 things on my todo list :
- check and adjust reluctor air gap
- replace fuel pressure regulator (ordering one)
- replace O2 sensor

Can you not swap the vacuum pot over to the new dizzy?

Not telling you how to do your work, but testing components is usually a lot more cost effective. If they require a special tool, well hey, it's the excuse to buy a new tool.

[AC439]

PM sent! Woohoo!!!
Can you not swap the vacuum pot over to the new dizzy?

Not telling you how to do your work, but testing components is usually a lot more cost effective. If they require a special tool, well hey, it's the excuse to buy a new tool.

Oh no worry Snooz. I did think about this too !

[Oldblueaccord]

I would disable the vacuum advance either pinch the hoses off or mechanically un hook it to rule it out. Drive it and see what you get.

[AC439]

Definitely will try swapping/disabling/enabling things out, too bad life gets in my way now so have to wait till next week. Will post findings...

[AC439]

Well, before I swap the dizzy, I was thinking about cleaning the injectors first. I followed the manual cleaning method for the injectors and they are now cleaned. Its hard to tell if one of the injectors were dirty. For that one injector, it took me a couple of tries to force injector cleaner through it after applying voltage to it. But at the end, they are all good passing injector cleaner.

Then I broke this part during reassembly (see pics, 2 from another member). FSM has no reference to this part on the thermostat housing. FSM only show A20A4 engine which does not have it. Mine is A20A3 so its different. Its a thermo-switch with 2 ports, labelles as "1" on the lower left side of the vacuum diagram Have absolutely no idea what it is for. I can see from the other member's picture, the vacuum hoses were disconnected and "jumped" through the small metal vacuum pipes with a short U shape hose.

Anyway, I JB welded mine back together and will put new vacuum hoses for connection....

Update: put the thermo-switch back together, top off coolant and road test after cleaning the injectors - absolutely no change, so dirty injector idea has been ruled out. Wait for a warmer day to switch out dizzy stuffs....