1996 Nissan Maxima 3.0 Liter V6.
THis vehicle had a timing belt replacement done as preventative maintenance.Ran fine bfore.Brought to us because it ran like crap after.Naturally we suspected improperly installed belt.Here's what we found:
Compression good on all cylinders. HOWEVER, cylinders 2 and 3 (right front and left middle respectively) were not firing.Moving coil packs caused no change.All ignition coil packs are receiving power from ECCS relay.Further testing showed affected cylinders were not having GROUND line cycled.Circuits remained grounded while other cylinders pulsed correctly.Diconnecting ECM broke ground on GROUND circuits,so we elimnated shorted wrining harness.Replacement ECU performs exactly the same.Labscoped both Crank sensors at wiring sub-harness connectors.Good scope.Scoped cam sensor at Cam sensor.Good scope.Checked continuity betwwen coil packs and ECU connector.All good(Already knew that because ECU was holding coils GROUND wire in grounded state.Visual inspection of Cam/Crank sensor teeth shows nothing unusual.What am I missing?
1996 Nissan Maxima 3.0 Liter V6.
THis vehicle had a timing belt replacement done as preventative maintenance.Ran fine bfore.Brought to us because it ran like crap after.Naturally we suspected improperly installed belt.Here's what we found:
Compression good on all cylinders. HOWEVER, cylinders 2 and 3 (right front and left middle respectively) were not firing.Moving coil packs caused no change.All ignition coil packs are receiving power from ECCS relay.Further testing showed affected cylinders were not having GROUND line cycled.Circuits remained grounded while other cylinders pulsed correctly.Diconnecting ECM broke ground on GROUND circuits,so we elimnated shorted wrining harness.Replacement ECU performs exactly the same.Labscoped both Crank sensors at wiring sub-harness connectors.Good scope.Scoped cam sensor at Cam sensor.Good scope.Checked continuity betwwen coil packs and ECU connector.All good(Already knew that because ECU was holding coils GROUND wire in grounded state.Visual inspection of Cam/Crank sensor teeth shows nothing unusual.What am I missing?
What sort of plugs are you running? I have had non-resistor plugs cause the ECU to wig out before and cause bizzare problems.
Mike
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What sort of plugs are you running? I have had non-resistor plugs cause the ECU to wig out before and cause bizzare problems.
Mike
Factory platimuns if I recall correctly.Would that cause the ECU to not break the ground on just these two cylinders? I don't see it, but thanks for the info.
Factory platimuns if I recall correctly.Would that cause the ECU to not break the ground on just these two cylinders? I don't see it, but thanks for the info.
I have seen ECU's randomly not fire coilpacks due to EMI caused by non-resistor plugs. I dunno you have all the same trouble shooting things I would have done. I would guess faulty power transistors next. A scarey place to be your are! Ever notice the better you are at troubleshooting the weirder things happen to you?
Mike
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I have seen ECU's randomly not fire coilpacks due to EMI caused by non-resistor plugs. I dunno you have all the same trouble shooting things I would have done. I would guess faulty power transistors next. A scarey place to be your are! Ever notice the better you are at troubleshooting the weirder things happen to you?
Mike
Yeah.The easy stuff gets fixed somewhere else.Since the Coil on plug transistors are all one unit I can rule that out, 'cause when I move the COP the dead cylinder doesn't move.
Yeah.The easy stuff gets fixed somewhere else.Since the Coil on plug transistors are all one unit I can rule that out, 'cause when I move the COP the dead cylinder doesn't move.
Yeah right you moved the coil packs. Crap I am completly stumped. Have you tried a continuity check of the harness while shaking it?
Have you tryed removing the ECU plug and pushing in the ends of the connector each time you turn the bolt a couple of revolutions? Sometimes the connector gets bowed and it will do werid things as well. I have seen some real smart people get their asses kicked by the connector getting bowed because they seated it simply by tunring the nut. Its a very common mistake.
Mike
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The pins on the ECU connector are so small and recessed that getting at them with a pick is impossible.Besides, the normal state on all these coil packs ( or at least the front bank,which has two working cylinders and one bad) is GROUNDED through the ECU, so if it wasn;t making connection at the harness it would show open.Instead the dead cylinder show steady GROUNDED when cranking/running while the good cylinders make/break GROUND.
I'm down to replacing the CAM sensor on the the timing cover.Based mainly on the theory that SOMETHING that was removed during the water pump replacement is to blame.The Cam sensor and two harness connectors are the only things electronically that were tampered with.And I can pretty much rule out the Harness connectors.I've cleaned them at bent the pins enough to get good connections,plus, I'm scoping everything right at the ECU so I know the signals are making it throught the sub connectors.Could a signal that is strong enough to trigger a SnapOn Vantage Labscope be not quite enough to make the ECU break ground? I wouldn't think so, the voltage spikes are right at 5 volts.Low aplitude? Its a head scratcher/
The pins on the ECU connector are so small and recessed that getting at them with a pick is impossible.Besides, the normal state on all these coil packs ( or at least the front bank,which has two working cylinders and one bad) is GROUNDED through the ECU, so if it wasn;t making connection at the harness it would show open.Instead the dead cylinder show steady GROUNDED when cranking/running while the good cylinders make/break GROUND.
I'm down to replacing the CAM sensor on the the timing cover.Based mainly on the theory that SOMETHING that was removed during the water pump replacement is to blame.The Cam sensor and two harness connectors are the only things electronically that were tampered with.And I can pretty much rule out the Harness connectors.I've cleaned them at bent the pins enough to get good connections,plus, I'm scoping everything right at the ECU so I know the signals are making it throught the sub connectors.Could a signal that is strong enough to trigger a SnapOn Vantage Labscope be not quite enough to make the ECU break ground? I wouldn't think so, the voltage spikes are right at 5 volts.Low aplitude? Its a head scratcher/
At this point I would do the same. 5 volts is normal. Let me know how this works out.
Mike
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There can only be one Icy Hot Stunta, Don't Hate.
I found info that possibly the the timing chain is 1 tooth off, this may cause the cam and crank sensor to be out of phase, it stated #2 and #3 coils, if you have solved the problem with out correcting the mechanical time PLEASE let me know. we have a similar problem, but deals with only 1 coil, left front of motor
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{*. . } trans side of motor
Front of car
Last edited by UPMDRM : Jan 19th, 2005 at 09:25 PM.
First.. why did the customer replace a timing chain that should never wear out?
stupid mistkae #1, but that's done and over with.
The other issue on these is that the cam sensor is very sensitive and can possibly be messed up. The guys that are doing VQ35 conversions in their 4th gens and trying to keep the 4th gen ECU for OBDI purposes have to re-machine this part and it's neither cheap nor easy. they're a fairly common failure point on these, so it's something to look at.
The other issue that I'm wondering about is both crank position sensors- the one on the flywheel and the one on the timing cover. I've heard of these getting covered in metal deposits from time to time and preventing the car form starting at all. most dealers say it requires replacing, but a simple clean & replace is usually all that's needed because they're covered in metal shavings. I highly doubt this is your problem since the ECU is receiving proper signals already and it's firing on 4 cylinders..
Otherwise you've got me stumped as well. strange stuff. might try replacing the cam sensor and PTU with known good ones and go from there. I hate to throw $$$$ parts at it, but you've eliminated just about everything else.
TIMING IS OFF, WE FOUND SLACK IN TIMING CHAIN WITH NEW TENSIONER AND GUIDE..... HAVE YOU HEARD OF STRETCH?? SLACK??? THE TIMING JUMPED 1 TOOTH, CAUSING THE CAM AND CRANK SENSORS TO BE OUT OF PHASE. CAUSING THE SENSORS TO GIVE BAD INFO. TO THE PCM. CAUSING THE PCM TO NOT! FIRE THE COILS 2 AND 3. THIS IS THE PROBLEM WITH REASSEMBLY AND OR DIAGNOSTIC. ANY QUESTIONS??
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