CPS Causing miss

[supradjza80]

Guys,

My car has a miss at idle and I have gone through and checked everything in the ignition system and believe the only culprit could be my CPS.

I have tried new spark plugs BCPR7ES at .028 just in case my Denso iridiums (IQ20's) were the cause, no change

All of the below items were ohm'd within spec
Plug wires (NGK's changed last fall) all were perfect
Ignition Coils
ISCV
TPS
02 sensor

The only thing that was out of range was the CPS, which ohms about 220-240 ohms on each of the three measurements. Now, I believe based on the above information that this is likely the cause of the miss. But the car starts every time, runs great in boost and has no issues like I would think a bad CPS would cause(random no starts/stalls). Since it is a 500$ part brand new (I want a new one), I would like to be certain it is the cause.

Has anyone else seen the CPS cause this sort of issue, but not have the car have starting/staying running issues?

Thanks,
Dave

[IJ.]

What's the air gap like in the CPS Dave?

[supradjza80]

What's the air gap like in the CPS Dave?

I did not check that since I have not had it off the car or the cap off recently. I know it says if it is out of spec you should also purchase a new one.

[IJ.]

Can't see why Dave it's adjustable, I bought a brand new CPS and it was so far out it wouldn't fire the MoTeC till I adjusted it.

[grimreaper]

i havent had the cover off in a while, how do you adjust the gap?

[CajunKenny]

There are screws on each of the two pickup coils that you loosen. Adjust the gap with the proper feeler gauge and re-tighten.

Rotate, then do the other side. Pretty easy...

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=IG&Page=16

And this if you're wanting to rebuild your own:

http://www.supramania.com/forums/showthread.php?t=44846&highlight=cps%2A+rebuild

[supradjza80]

Can't see why Dave it's adjustable, I bought a brand new CPS and it was so far out it wouldn't fire the MoTeC till I adjusted it.

Ahh ok, well I just read this part of the service manual and figured it was not adjustable

"If the gap is not within specification, replace the cam position sensor."

I will check it later this week or maybe this weekend and see what I find out.

That said does anybody know if being out of the range for resistance can cause a problem? I don't believe the air gap and resistance are related but maybe (electrons really are not my forte).

[CajunKenny]

The CPS generates a digital pulse/frequency every time the signal rotor passes through the magnetic field of the pick-up coils. G1 and G2. This digital pulse/frequency allows the ECU to calculate/detect the engine speed and position.

If the referred air gap is greater than spec, the pulse will be weak in amplitude, short in pulsewidth, or both. This would result in a miss.

If the resistance is too high across the pickup coil, it has roughly the same affect as too great of an air gap.

If you have both...severe idle problems and starting issues.

[supradjza80]

^^^ Thanks :)

[CajunKenny]

Glad I could help. :)

Good luck and keep us posted on what you find.

[supradjza80]

Alright, I checked the gaps on the pickups, one of them was just out of range. I but them both right down to .008" and did the NE pickup as well since I was in there. Put it all back together and it is still the same, I still have the miss.

Any thoughts?

I will add some pictures of the inside of the sensor, it still looks brand new...

[supradjza80]

Alright pictures.

First - Is it normal for the factory wiring to the CPS to have splice in it? I took the old crappy electrical tape wrap off of the wiring and re-wrapped it with scotch Super 88

unwrapped
http://i327.photobucket.com/albums/k463/supradjza80/P1010092.jpg

wrapped
http://i327.photobucket.com/albums/k463/supradjza80/P1010101.jpg

Now to the interior of the CPS (it has a recently replaced gasket and factory plastic cover)

Camera sucks even on micro... but its the only pic of the "gap"
http://i327.photobucket.com/albums/k463/supradjza80/P1010098.jpg

overall pic
http://i327.photobucket.com/albums/k463/supradjza80/P1010094.jpg

I was hoping this might fix it but once i measured the gaps with my feeler gauges I was doubtful it would do anything. Just waiting for it to warm up to time it it was starting to miss...damn car :)

[thevork]

I just saw this thread and I got really curious about how much your car misses @ idle.
Is it constantly or every 5 to 10 seconds ?

This because my car does this too after upgrading to 550cc+lexus afm, and two other supras with a similar setup do also miss every 5 to 10 seconds @ idle so we figured it to be "normal" behaviour caused by the lexriemer mod.
The only thing I saw on these boards that probably fixed this was the COP mod.

Don't know if this helps, but just making sure you're not chasing ghosts. :)

[supradjza80]

I just saw this thread and I got really curious about how much your car misses @ idle.
Is it constantly or every 5 to 10 seconds ?

This because my car does this too after upgrading to 550cc+lexus afm, and two other supras with a similar setup do also miss every 5 to 10 seconds @ idle so we figured it to be "normal" behaviour caused by the lexriemer mod.
The only thing I saw on these boards that probably fixed this was the COP mod.

Don't know if this helps, but just making sure you're not chasing ghosts. :)

yeah, i may be chasing a ghost in this case. Ill take a video of it at idle put it kinda sounds like popcorn every 5-10 seconds (doesn't do it during warm up but does do it constantly while warm). I am still stock afm/stock injectors/stock pump. just some other bolt ons. Thing is my car went from not doing the pop (all last year) and this year just started to miss at idle and even continues to do it if you hold it at a constant slightly raised rpm with no load. If its normal that's fine but I just don't think that is the case. AFR's at idle are in the 14.3-15 range so it appears it is nothing to do with warm up enrichment not turning off (haven't checked the temp sensor)...anyway I gotta go to bed, the morning is going to come early!

[CajunKenny]

I have to say that tracking down a slight miss or hiccup in idle can be maddening! Have you checked for codes?

That said, I'll throw out some of the things that I've seen and hopefully some other folks will too.

An oil leak in the spark plug galley can cause issues when there is enough oil (typically around #6) around a plug/plug boot to cause the plug to ground out to the head.

Bad Plugs and Plug Wires.

Incorrect Plug Gap.

Vac Leaks.

And one last thing that I experienced with a miss/hiccup in idle is that after replacing the injector o'rings and insulators things improved two fold. Basically, all of the rubber parts related to my injectors were dried and cracked.

The inside of your CPS looks CLEAN by the way!!! :)

[dumbo]

Have you done the external ground on the igniter? I recomend it, it only takes 15 minutes and two or three dollars.

On a side note, mine randomly does miss when warm eary 5-10 seconds, but only occasionaly. Maft pro speed density. So who knows..

[3p141592654]

Looks like the pickups were replaced and the CPS rebuilt, or its nearly brand new.

Did you get measurements for the gaps? Also, is the top reluctor flush with the top of the G1/G2 pickups?

[supradjza80]

Looks like the pickups were replaced and the CPS rebuilt, or its nearly brand new.

Did you get measurements for the gaps? Also, is the top reluctor flush with the top of the G1/G2 pickups?

I believe it is still the original CPS from the car. That said, the gaps for g1/g2 were pretty good as they were. One of them was just out of range (don't remember which). that said I adjusted all 3 of the gaps down to .008" and yes the reluctor is flush with the tops of the pickups.

[3p141592654]

Then I'd say the CPS is not your source of the problem. You can test it by hooking it up on the scope and spinning it. Should get at least 20V peak to peak at 3000 rpm.

[supradjza80]

Then I'd say the CPS is not your source of the problem. You can test it by hooking it up on the scope and spinning it. Should get at least 20V peak to peak at 3000 rpm.


Well I am not smart enough electronically to know how to properly use a scope (I assume you are saying oscilloscope)...Anyway as promised here is the vid of the idle.

http://www.youtube.com/watch?v=81KKP4mK_YI

[thevork]

I have that too and am not bothered by it although ofcourse mine is modified in some way (lexriemer) and yours seem to be stockish.

I'd point at the coilpack/wires/ first but hey that's just me.

[supradjza80]

I have that too and am not bothered by it although ofcourse mine is modified in some way (lexriemer) and yours seem to be stockish.

I'd point at the coilpack/wires/ first but hey that's just me.

well, coil packs all ohm fine, wires ohm fine and are NGK's bought last fall. Plugs were changed at the same time to Denso Iridiums, so tried new NGK coppers, same problem with .028 gap.

[supradjza80]

http://www.youtube.com/watch?v=F747dexc_r8

here is a video of the car under boost from the same day. No missing while under power.

[dumbo]

Did you try the external ignitor ground?

[CajunKenny]

An awful lot of supras out there have a slight idle stumble or miss. Mine included. When I first got mine it didn't stumble at all. It idle'd smooth and perfect.

I got a bhg and after repairing that, I got the typical idle stumble/miss. As with yours, mine is fine in all other ways. Power is good, no hiccups under throttle, etc...

My buddy just got a 91T and his idle is perfect! He's stock though.

I don't know man....I wouldn't say that your idle is "normal"; but, I would say that it's typical of our cars. Now if you EVER figure it out, LET ME KNOW!!!! ;)

Nice car by the way. And a 1992 to boot! :)

[supradjza80]

Did you try the external ignitor ground?

Nope haven't done this yet, I guess I will try that next. It seems to be a common consensus that the CPS could not be the cause just due to higher than normal resistance so I have to keep trying things.


An awful lot of supras out there have a slight idle stumble or miss. Mine included. When I first got mine it didn't stumble at all. It idle'd smooth and perfect.

I got a bhg and after repairing that, I got the typical idle stumble/miss. As with yours, mine is fine in all other ways. Power is good, no hiccups under throttle, etc...

My buddy just got a 91T and his idle is perfect! He's stock though.

I don't know man....I wouldn't say that your idle is "normal"; but, I would say that it's typical of our cars. Now if you EVER figure it out, LET ME KNOW!!!!

Nice car by the way. And a 1992 to boot!

Well we have something slightly in common here. When I first got my car and all last year (about 10,000 miles put on the car last summer while slowly upgrading it and doing basic maintenance) The car had a perfectly smooth idle.

Then I stored it all winter and a few days after I took it out the Water outlet gasket where it meets the head started leaking really bad (took it apart and one of the bolts was missing and the gasket had shifted. To do this I had to take out the CPS. I put everything back together and right away after that I it began missing (before I timed it even). This lead me to beleive after checking so many different things that it was caused from the CPS since I had messed with it just prior to the miss beginning. And when I tested the Resistance and saw it out of spec I thought I had my answer, but who knows. Anyway the car has idled with the miss ever since.

I will try the igniter ground trick to see if that fixes it but I'm not holding my breath.

And thanks for the kind words on the car, I have been pretty lucky so far with it, and I'm pretty happy its a 92, although I would have been happy with any clean 89+:naughty:

[CajunKenny]

The igniter ground mod is definitely worth your time. Even if it doesn't fix the idle, it's a preventative thing. It's something I plan on doing this winter myself.

I am also going to completely rebuild one of my spare CPS's this winter. I plan on doing the whole thing, including all wires.

[redma70]

Im having the same problem with my N/A. It has a miss that makes the car backfire every once in a while when im idling. I checked my plugs and they were massively gummed up with carbon residue. Would this be related to supradjza80's problem but his being CPS and mine distributor??

[CajunKenny]

I checked my plugs and they were massively gummed up with carbon residue. Would this be related to supradjza80's problem but his being CPS and mine distributor??

Nope he changed out his plugs. :)

[nosechunks]

Looks like the pickups were replaced and the CPS rebuilt, or its nearly brand new.

Did you get measurements for the gaps? Also, is the top reluctor flush with the top of the G1/G2 pickups?

Any place to source new pickups? im going to be rebuilding my CPS because of the oil leak and the wires are so hammered the insulation cracks if you move them.

I would LOVE to put new coils into this thing, especially because im going standalone and i want as many new sensors as possible.

[3p141592654]

I'm not aware of a source for the pickups. In my case I re-potted the epoxy that was cracking, but I never swapped out the wires.