Timing Jumping Around
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Timing Jumping Around
I just installed a new engine into my '90 coupe, and I can't get the timing to stay still.
I think I've set the timing 3 times, and even with getting the distributor hold down clamp as tight as I can with a wrench it keeps advancing by 2-3 degrees. I've disconnected the EST wire by the firewall each time I've set and checked the timing.
Something I noticed was that even with the EST wire disconnected, revving the engine causes the timing to jump ~10 degrees, from 6 to about 16. It jumps very abruptly, almost immediately, as I slowly raise engine speed. Since it doesn't have vacuum or mechanical advance, I don't think it should be doing this and thought this might be related?
Edit:
Just found out my dad swapped wires #2 and #4 when he plugged them in. Not sure if this could have a bearing on timing?
I think I've set the timing 3 times, and even with getting the distributor hold down clamp as tight as I can with a wrench it keeps advancing by 2-3 degrees. I've disconnected the EST wire by the firewall each time I've set and checked the timing.
Something I noticed was that even with the EST wire disconnected, revving the engine causes the timing to jump ~10 degrees, from 6 to about 16. It jumps very abruptly, almost immediately, as I slowly raise engine speed. Since it doesn't have vacuum or mechanical advance, I don't think it should be doing this and thought this might be related?
Edit:
Just found out my dad swapped wires #2 and #4 when he plugged them in. Not sure if this could have a bearing on timing?
Last edited by C4ProjectCar; Aug 10, 2015 at 05:15 PM.
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 278
From: Melbourne, Victoria, Australia
I just installed a new engine into my '90 coupe, and I can't get the timing to stay still.
I think I've set the timing 3 times, and even with getting the distributor hold down clamp as tight as I can with a wrench it keeps advancing by 2-3 degrees. I've disconnected the EST wire by the firewall each time I've set and checked the timing.
Something I noticed was that even with the EST wire disconnected, revving the engine causes the timing to jump ~10 degrees, from 6 to about 16. It jumps very abruptly, almost immediately, as I slowly raise engine speed. Since it doesn't have vacuum or mechanical advance, I don't think it should be doing this and thought this might be related?
Edit:
Just found out my dad swapped wires #2 and #4 when he plugged them in. Not sure if this could have a bearing on timing?
I think I've set the timing 3 times, and even with getting the distributor hold down clamp as tight as I can with a wrench it keeps advancing by 2-3 degrees. I've disconnected the EST wire by the firewall each time I've set and checked the timing.
Something I noticed was that even with the EST wire disconnected, revving the engine causes the timing to jump ~10 degrees, from 6 to about 16. It jumps very abruptly, almost immediately, as I slowly raise engine speed. Since it doesn't have vacuum or mechanical advance, I don't think it should be doing this and thought this might be related?
Edit:
Just found out my dad swapped wires #2 and #4 when he plugged them in. Not sure if this could have a bearing on timing?
Hi
Does the engine run smoothly, or does it miss a beat here and there?
I think the 1990 was the first without a MAF sensor, is your MAP sensor ok and wiring connected securely?
I would also check the throtte position sensor, check the volts are stable and within spec.
Check the ignition leads with a multimeter at each end, check the distributor timing is correct. The injector connectors, did you remove them by tugging at the wires???
I found out the small metal strip in the connector can be broken, it may show 12 volt pulses when checking with a multimeter but not be able to pass enough to operate the injector.
A good way to check all cylinders are working when engine is cold, start the car and run for 10 or 20 seconds and turn off.
Check each exhaust pipe temp, if you have a cold header pipe you know where to look.
Check compression, that can tell you if the valve lash is ok and valves are closing fully.
Have you tried disconnecting the ecm wire or battery, remember the ecm will try and compensate for anything out of spec. It can get itself in knots.
Should be something simple, good luck.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Hi
Does the engine run smoothly, or does it miss a beat here and there?
I think the 1990 was the first without a MAF sensor, is your MAP sensor ok and wiring connected securely?
I would also check the throtte position sensor, check the volts are stable and within spec.
Check the ignition leads with a multimeter at each end, check the distributor timing is correct. The injector connectors, did you remove them by tugging at the wires???
I found out the small metal strip in the connector can be broken, it may show 12 volt pulses when checking with a multimeter but not be able to pass enough to operate the injector.
A good way to check all cylinders are working when engine is cold, start the car and run for 10 or 20 seconds and turn off.
Check each exhaust pipe temp, if you have a cold header pipe you know where to look.
Check compression, that can tell you if the valve lash is ok and valves are closing fully.
Have you tried disconnecting the ecm wire or battery, remember the ecm will try and compensate for anything out of spec. It can get itself in knots.
Should be something simple, good luck.
Does the engine run smoothly, or does it miss a beat here and there?
I think the 1990 was the first without a MAF sensor, is your MAP sensor ok and wiring connected securely?
I would also check the throtte position sensor, check the volts are stable and within spec.
Check the ignition leads with a multimeter at each end, check the distributor timing is correct. The injector connectors, did you remove them by tugging at the wires???
I found out the small metal strip in the connector can be broken, it may show 12 volt pulses when checking with a multimeter but not be able to pass enough to operate the injector.
A good way to check all cylinders are working when engine is cold, start the car and run for 10 or 20 seconds and turn off.
Check each exhaust pipe temp, if you have a cold header pipe you know where to look.
Check compression, that can tell you if the valve lash is ok and valves are closing fully.
Have you tried disconnecting the ecm wire or battery, remember the ecm will try and compensate for anything out of spec. It can get itself in knots.
Should be something simple, good luck.
I'm not sure if the MAP has any issues, but the wires are all connected to it.
TPS volts are stable. In my most recent data log, it starts at .31v and maxes at 4.24. I don't know what "spec" is for the self-calibrating throttle position sensors, but the TPS % data is accurate.
The ignition leads are the spark plug wires, right? What am I testing for, resistance?
Checking temps is a brilliant idea. Can't believe I never thought of that!
Okay, I'll also check compression when I can. Hope I can fit all the repairs and tests I need to do in between now and leaving for college.
I have disconnected the battery to reset the ECM several times just today.
Thanks for the help!
I thought that causes erratic jumping, not slowly-slipping timing, right? I posted a picture of the cam gear within the last ~20 (wild guess) miles and was told wear was acceptable. I'll keep that in mind though, thanks.
Brand new damper. Thanks for the idea though.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
I tried to see if I could turn it, but I stopped being able to do so far before the clamp was all the way tight.
I just went on a couple runs after resetting it to 6* and the timing hasn't changed. So fingers crossed, hopefully the problem is gone. Maybe it had something to do with the switched wires.
I'll keep checking it and if it changes I'll go through all the suggested steps (although a few of them sound like a good idea anyway, like the compression check).
I just went on a couple runs after resetting it to 6* and the timing hasn't changed. So fingers crossed, hopefully the problem is gone. Maybe it had something to do with the switched wires.
I'll keep checking it and if it changes I'll go through all the suggested steps (although a few of them sound like a good idea anyway, like the compression check).
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Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
Something I noticed was that even with the EST wire disconnected, revving the engine causes the timing to jump ~10 degrees, from 6 to about 16. It jumps very abruptly, almost immediately, as I slowly raise engine speed. Since it doesn't have vacuum or mechanical advance, I don't think it should be doing this and thought this might be related?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
In that thread he writes:
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
I actually already had and fixed that problem. I had pinched the O2 sensor wire under a ground stud nut, but I fixed it and painted the exposed wiring with liquid tape (couldn't reach electrical tape up there and thought it might melt anyway).
For some odd reason when it shorts it shows 4.42 mV on the O2 sensor, which I have not seen since I fixed it.
I doubt it. It would be tough to find and I don't have time to track one down in the few remaining days before I leave for college.
How would a faulty ECM affect timing with the EST wire unplugged?
For some odd reason when it shorts it shows 4.42 mV on the O2 sensor, which I have not seen since I fixed it.
I doubt it. It would be tough to find and I don't have time to track one down in the few remaining days before I leave for college.
How would a faulty ECM affect timing with the EST wire unplugged?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
[ EDiT ] I just read on another forum that the non-adjustable TPSa started in 1990. [ /EDIT ]
It's a function of the ECM/PCM. In later cars the PCM looks at the TPS voltage at ignition-on and calls that "idle".
Last edited by Cliff Harris; Aug 13, 2015 at 12:37 AM. Reason: Added clarifying note.