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Old 06-20-2012, 07:28 PM   #1
Jim Geo7
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1988 D21 z24i acceleration problems.

I had several problems that have cropped up over time due to deferred maintenance. A few months ago the engine became unresponsive to any throttle input above half of the peddle. I replaced the ECU and found that, that didn't help but while trying to diagnose the problem I found conditions consistent to a blown head gasket. I then found the gasket had been in good condition but the head was cracked. I replaced the head and made sure the timing chain went back together exactly as it had been. Ran the engine to temp and let it cool over night then loosened and re-tightened the head bolts. Then I ran the engine to temp and re-adjusted the valve lash. I went to drive it and found the engine had no acceleration. However, it idles fine. I swapped out my replacement ECU for my old one (better a devil I know) and found no change. This is off the curb low speed acceleration not being present not "freeway speed" loss of acceleration with both ECU. With a little research I became suspicious of having no spark on the intake side of the engine. When tested I found ZERO spark. Apparently the intake side is the side that is advanced and the exhaust side is static at 10 degrees BTDC. It seems to fit that if I have no spark to advance I'd lose power as the engine RPM is increased. So now my questions does anyone know how to fix this? Is there a tool that I can plug into the socket ahead of the coil to see if there is a signal coming from the ECU? I've checked both coils for resistance as per the repair manual and both seem to check out OK. FWIW About 10 years ago I replaced an ECU for being unresponsive to the top half of my peddle and that fixed the problem at that time. This seems to be a nother dog though.
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Old 06-22-2012, 02:58 AM   #2
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Re: 1988 D21 z24i acceleration problems.

More information: The ECU is not the problem.
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Old 06-23-2012, 04:18 PM   #3
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Re: 1988 D21 z24i acceleration problems.

Read codes today. 12 and 21. Airflow meter and ignition signal. My hunch was becoming that it was one or the other. Both is a bit dis-heartening. I'll try replacing the MAF first. Then if that doesn't solve it I'll re-build the crank angle sensor.
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Old 06-24-2012, 01:24 PM   #4
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Re: 1988 D21 z24i acceleration problems.

Well that was stupid. Air flow meter and throttle position sensor weren't even plugged back in after putting the rebuilt head on. Condition now, runs even worse than it did but no error 12. Error 21 looks to be a very generic code but I'm leaning toward a bad crank angle sensor rather than a bad power transistor.

Last edited by Jim Geo7; 06-25-2012 at 12:40 PM.
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Old 06-25-2012, 09:47 PM   #5
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Re: 1988 D21 z24i acceleration problems.

Today I went to the local "Pick a Part" to try to find a coil and transistor and found myself a nice well kept Nissan Eighty Six and a half Pathfinder, actual manufacture date was 11/86. It had two coils that match the style of my truck and looked to be low mileage and very well maintained. Except for a badly crunched right hand side it would probably still be on the road. Everything left under the hood looked good and seemed to be Nissan Dealer maintained. I took the intake side ignition coil out and am thinking that it's reasonable to guess that if it doesn't fix my problem it will be a good indication of a bad crank/cam angle sensor. As of the last engine start (this was done yesterday, I'm waiting for better weather to replace the coil. Yup that's right I've done all this work on the curb in front of my house.) it will idle smoothly for about ten seconds at about 800 rpm and then just die. It restarts just fine then dies after about ten seconds. It does that basically all day long. Absolutely undrivable. Any ideas in case I'm all wrong?

Last edited by Jim Geo7; 06-26-2012 at 03:44 AM.
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Old 06-29-2012, 06:41 PM   #6
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Re: 1988 D21 z24i acceleration problems.

Possible thread ender. Replaced distributor/crank angle sensor with a rebuilt distributor and fixed the problem. Returned original ECU to service. All that's left is to perfect an imperfect timing issue. Hope this thread helps somebody someday. No ECU codes.

Last edited by Jim Geo7; 07-19-2012 at 02:45 PM.
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Old 07-15-2012, 01:48 PM   #7
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Re: 1988 D21 z24i acceleration problems.

Hmmm OK so it's not an imperfect timing issue. I'm continuing to have a rough running engine during idle. I've readjusted my fast idle adjustment as per the book and when I start the engine cold it idles way to slow (under 500 RPM). When warm it runs as it should (acceleration and idle are fairly normal though not perfect) and drives OK. One thing I know is an issue is that my Anti Backfire valve doesn't work correctly. It seems to be pulling air full time from the air-cleaner, as in, it's a huge vacuum leak and causes massive fuel use. Since I can't find a new one I've done a temp fix by blocking the port with duct tape until I do find a replacement.
Beyond that though, My focus is becoming the Fast Idle Control Device or F.I.C.D. I'll be checking my codes this afternoon since I've driven it enough for it to have set codes if it's an electronic problem.
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Old 07-19-2012, 02:42 PM   #8
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Re: 1988 D21 z24i acceleration problems.

Continuing saga, Removed the anti backfire valve and blocked the anti backfire port with a half inch dowel. Slightly improved idle. I removed the EGR valve and found what looked to be a point of vacuum leak at the stainless steel pipe connection to the EGR. Cut the Stainless tube in two and crimped the ends till sealed, cleaned up the attachment point of the valve and re-installed everything extra tight then blocked all vacuum sources to the valve. re-installed crimped stainless tube to exhaust manifold. Though the engine still has issues this has made the biggest difference in the performance of the engine. Still no ECU codes. Will readjust idle settings today.
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