A Big 6 running on only 4?

[Happy_Go_Lucky]

Hey guys, I am back. I have been searching threads, but cannot find one similar to what I am experiencing. It feels as though my 535 is running on only 4 pots - but thats not the case. Here is a short synopsis. Very difficult to start - cold, warm or hot. Takes the better part of a few minutes to get her fired up. No idle to speak of, extremely rough. Bang her up to 2, 3, 4 or even 5k rpm, still rough as the fur on the back of a Gator! All through the rev range, she is rough. Miss firing, farting and spluttering. When she's at idle (lets call it an idle), disconnect plug from AFM - no change. Reconnect, no change. Disconnect plug from throttle possition switch - no change. Reconnect, no change. With TPS disconnected, increase revs - still rough. But every so often, just for a few seconds, she becomes smooth. She's smooth as often as a motor is rough with an intermittend missfire. Replaced fuel filter, fuel pressure regulator, cleaned injectors, checked plugs and leads .... I'm stumped. Any ideas, thoughts?

[filip00]

try to take someone elses air flow sensor and see if maybe yours is broken.

[Ferret]

I'm tempted to say this is probably an ignition fault if it's misfiring all the way though the rev range - probably a weak coil or a dizzy that's falling apart inside.

Check the impedances on the ignition coil, and whip off your distributor and have a look inside.

Next I'd have to go with checking your injectors arent sticking and/or your fuel pressure's good.

:)

[Bin_jammin]

Have you got a DMM? Set it to ohms and check the resistance on each plug wire. Do this by putting one lead on one end of a plug wire, and the other end on the other. Remember that you're going to see more resistance with an increase in length, make a matrix of it and look to see if any are out of place. Cap and rotor changed? It sounds like you've got a wicked skip.

Considering this is an m30, check your compression. Have you notoced any coolant loss recently? You're lucky, it's so much easier to diagnose a problem where the car will occasionally run smooth rather than occasionally run rough :)

[Happy_Go_Lucky]

Have you got a DMM? Set it to ohms and check the resistance on each plug wire. Do this by putting one lead on one end of a plug wire, and the other end on the other. Remember that you're going to see more resistance with an increase in length, make a matrix of it and look to see if any are out of place. Cap and rotor changed? It sounds like you've got a wicked skip.

Considering this is an m30, check your compression. Have you notoced any coolant loss recently? You're lucky, it's so much easier to diagnose a problem where the car will occasionally run smooth rather than occasionally run rough :)

Plug HT leads check out fine, all in spec. Cap and Rotor still original (a possible cause maybe). Compression not checked recently, but I rebuilt the motor not too long ago (about 15,000 km back) - re-sleaved, new rings, etc... compression *sounds* and *feels* good. I am still leaning towards a sensor of some sort ... but don't know where to start. Thanks for the feedback. Forgot to mention ... no coolant loss at all :)

[Ferret]

Plug HT leads check out fine, all in spec. Cap and Rotor still original (a possible cause maybe). Compression not checked recently, but I rebuilt the motor not too long ago (about 15,000 km back) - re-sleaved, new rings, etc... compression *sounds* and *feels* good. I am still leaning towards a sensor of some sort ... but don't know where to start. Thanks for the feedback. Forgot to mention ... no coolant loss at all :)

Electrically check the ignition coil.

[leicesterboy15]

Is it over fueling? I had a vacuum leak that caused my car to do a similar thing although sometimes it was worse than others, it wasn't constantly bad but it was there through the rev range. On mine it turned out to be a split in a breather pipe that (from memory) goes from the front of the block, through and under the exhaust manifold and up into the bottom of it (sorry not the best description). This was causing the car to over fuel and made it run rough through the rev range.