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intermittent jumpy tach - new disty = works now!


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13 replies to this topic

#1 hooziewhatsit

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Posted 13 August 2005 - 07:40 PM

87 SPFI wagon, 259K miles, manual,

Just got the engine back in after doing a HG/reseal job. Ran fine for a few days on blocks, then the tach decided to start jumping around. It always matches the engine RPM while it's running. Most of the time it will run fine until I put some load on the engine by turning on the AC, etc. At first it seemed like it ran out of gas, but even after adding more it didn't help it.

While trying to start the car when it isn't working, the tach will jump all the way around and peg itself. There is also no spark from the coil.

There is NO slop or play in the distributer bushings that I (or a friend) can feel. I've replaced the coil with one from another of my other cars to no difference. I put the coil from this car in the other car, and it runs just fine. So, it shouldn't be the coil. I cleaned all the grounds while I was at it also.

To test the distributer, I've taken the distributor out of the engine but left it plugged in so I can manually trigger the coil by spinning the rotor, without turning over the engine. This works most of the time. Using cougars advice from another thread, I monitored the voltage at the neg side of the coil, and most of the time it changes with the spinning rotor.

I've also checked all the wiring from the ECU to both the distributer and the coil, and it checks out fine.

any ideas?

thanks in advance
-Dave

ps, sorry for the long winded description


edit: did some more tinkering this evening...
After making it fail by adding a load, I turned the engine off, then disconnected the coil wire. I placed the coil wire by ground to watch it spark. I turned the engine over by hand with the key on, and it would occasionally spark like it should. :confused:

#2 hooziewhatsit

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Posted 15 August 2005 - 09:45 AM

third page bump for the monday morning work folks :)

later today I'm going to try swapping the disty out with one from another car. I'll have to take the connectors off and swap them though, should be fun :drunk:

#3 puttputt

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Posted 15 August 2005 - 04:30 PM

third page bump for the monday morning work folks :)

later today I'm going to try swapping the disty out with one from another car. I'll have to take the connectors off and swap them though, should be fun :drunk:


Looking at the WD's, I don't see a physical path between the dist to the coil, except thru the ECM... as I would expect. Because the transistor on the coil amplifies the dist pulse via the ECM, and not directly from the dist, I believe your problem would likely be on the coil side of the ECM, wouldn't it?.... maybe even the transistor itself, or possibility the (gulp!) the ECM. Personally, I'd suspect the tach signal source wire. Have been under the dash yet?

BTY Hoozie, what years CAS will interchange on my '87 SPFI - EA82? Wire colors are obviously different between some years, but what about potentual differences in the opti triggers? '87 supplies here in Idaho appears to have dried-up. I might need a ECM also as i'm getting 500mv from the (body side) of the CAS connector (the black wire). Thought it was suppost to be a ground? ~putt~

#4 MorganM

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Posted 15 August 2005 - 04:44 PM

Try swaping on a different alternator.

#5 deej

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Posted 15 August 2005 - 04:47 PM

i have an 86 turbo xt and it was doing the same thing , as soon as i put a new alternator in my problem was solved.

#6 hooziewhatsit

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Posted 15 August 2005 - 04:57 PM

Try swaping on a different alternator.


interesting... that's a much quicker swap than what I was thinking... thanks for the idea (deej also)

come to think about it.. the idiot lights did usually come on for a second or two when it first starts, but I accounted that to a very low idle (200-400ish rpms)

#7 deej

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Posted 15 August 2005 - 05:00 PM

yes your idle is way to low i have mine at 900-1000 and its fine plus it has better response off the line.

#8 hooziewhatsit

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Posted 15 August 2005 - 05:45 PM

:banghead: Same thing.. Although it did take longer to die with the good alternator :confused:

Like before, after the tach/engine jumped around and died, I took the coil wire off and cranked the engine by hand. It would occasionally spark, where it should spark often with each quarter turn of the engine.

So to recap...
-new coil
-new alternator
-clean grounds
still jumps around and dies

I have another disty but with a different connector. I could swap it in if I have to, although I'm going to wait until it cools off out there (fricken hot in the sun, I need a garage)

about the idle, it's also saying the IAC is broken, but the relay is just fine and I've cleaned it out(??). regardless, I should be able to keep the RPMs around 2000-3000 and not have it die when I turn on the AC.

Thanks,
-Dave

#9 MorganM

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Posted 16 August 2005 - 04:20 PM

All jumpy tachs ive seen settled down with new alternators.

Welp the tach is wired directly into your ignition circut; so we kinda have it narrowed down. Got another ignition amp thingamajig to swap on? Its the dealybob on the coil bracket there that makes you go "huh?" when you look at it :)

I know... I'm very technical :grin:

#10 hooziewhatsit

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Posted 16 August 2005 - 04:30 PM

All jumpy tachs ive seen settled down with new alternators.

Welp the tach is wired directly into your ignition circut; so we kinda have it narrowed down. Got another ignition amp thingamajig to swap on? Its the dealybob on the coil bracket there that makes you go "huh?" when you look at it :)

I know... I'm very technical :grin:


guess I forgot to mention that when I swapped coils, I swapped the whole assembly, including the ignition amp thingy.

This morning when it was cool out it ran long enough to warm up (even had the AC on), then it sputtered and died :confused: Could this somehow be related to the CTS? I just tried to start it again (90+ *F out) and it did not want to start.

I also checked continuity on all wires from the disty/ignition amp to the ECU, and they're fine (or just didn't break even while I wiggled them around).

I have to take my 91 loyale down for a couple days to replace the water pump (see my boom goes the radiator hose thread) and can swap the disty out if I need to. I'm assuming the distys are the same inside. I may take the 91's apart just to make sure though.

thanks,
-Dave

#11 karinvail

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Posted 17 August 2005 - 04:18 AM

so, it starts when cold, but dies when warmed up? That is exactly what my lawnmower was doing - and it had a bad coil. Do you have a spare to check to see if yours is good? I know you said it's new, but I have gotten new parts that ended up bad on many occasions............just a thought........

#12 MorganM

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Posted 17 August 2005 - 11:14 AM

I'm assuming the distys are the same inside. I may take the 91's apart just to make sure though.

thanks,
-Dave


They are both EA82 SPFI; same dizzy. Swap away!

Does it stay running if you get on the throttle?

#13 hooziewhatsit

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Posted 17 August 2005 - 03:49 PM

new distributor = fires right up and runs!!! :banana:

bad distributor in other car = no worky
Conclusion: the CAS is bad.

So, off to the JY for a new distributor for the car that now doesn't work.

Thanks for the help everyone.

I'm still perplexed as to why it decided to die when it did. Would've bugged the heck out of me if it died while the engine was out. I would've thought I had something screwed up somewhere.

thanks,
-Dave

#14 MorganM

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Posted 17 August 2005 - 04:00 PM

Glad you found the culprit.

Electronic devices do that.... work fine then out of no where they fail :(




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