Defender405

This has me scratching my head, hopefully one of you has some insight. The Z would crank but wouldn't fire up at all. Car runs strong and with one exception has always started up for me every other time so this is unusual. I check all of the wiring and fuel system, I'm getting gas and I have spark, the plugs are wet. I check posts here and see where someone advises pulling the fuel pump fuse and cranking the engine over to get excess fuel out of the cylinders. I do this and she fires up and runs for 15-20 seconds, burns off all of the fuel in the system, and then dies. I plug the fuel pump fuse back in and she won't start again, does the same crank but not fire routine. Pull the fuse and she starts back up again, re-install the fuse and she stays running just fine. The other time it wouldn't start it acted the same and after sitting for a few days seemed to fix itself, so I assume it was just "flooded" that time too. Both times were on short trips (approx 2-3 miles) where the car had warmed up but wasn't hot by any stretch of the imagination. I thought maybe vapor lock or something the first time (it was a hot day) but today it was barely 60 degrees and it acted the same so I'm sure the problem was the same both times. The FSM wasn't terribly enlightening on the issue. Any of you have ideas on what may be happening here that is causing me to "flood out" from time to time?

masterhufflpuff

If the cylinders are getting too much fuel, then the spark plugs will get doused which won't allow for sparking, hence the no start. So i'd start checking anything and everything that has to do with fuel delivery, and fuel sensory.

rogerz

that is a toughie since it doesn't seem to happen with regularity. The obvious choice is the chts because (at least my experience) when you get odd things happening when the car is between cold and runnng temp the chts is often the cause. next up would be the O2 sensor which you can unplug and then see if the non start still happens. take a lot of short trips. here are some things to look at and do that might eliminate a problem
Get your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen. Usually on a rainy night around Oh Dark Thirty.

Clean the connectors for the maf or afm, ecu and tps. Deoxit by CAIG is probably the best connector cleaner on the market. spray with CorrosionX after cleaning and before putting together this will help prevent any further corrosion. DON'T USE DIELECTRIC GREASE.

Defender405

Any ideas which fuel system component would do this in such an inconsistent manner? When I have checked the system out previously everything checks good, but that is when it's not messing up. Both times it has had this issue it has been somewhere that extensive mechanic work would be inconvenient and likely get me in trouble. Anybody got a good way to find a bad component when it is working correctly enough to look like it is good?

Defender405

Thanks RogerZ, I will try to disconnect the sensors and clean the leads up as well as I can. The battery is solid, cranks good and shows good 12V consistently. My terminals are good solid units and I have another ground running to the passenger side strut mount, so I'm pretty sure voltage isn't the issue. I have had some corrosion on electrical leads since it's an Iowa car. I had to clean the fuel injector leads, so it wouldn't surprise me if I have corrosion on the various sensor leads. I will check that tomorrow and report back.

rogerz

one thing that can happen but usually when everything is really hot is that the ignitor for the coil is close to failing and when it gets hot does that. freezespray it when you get the failure and see if you can start then. the fact that the plugs are wet might indicate spark failure but also easy to flood the engine trying to start repeatedly. Maybe try a little more air into the engine by using the accelerator slightly. do a ohm test on the chts data in the fsm free from xenon31 if you do not have a copy.

Defender405

Sensor leads all looked OK, but I cleaned them up and corrosion sprayed them anyway. I'm concerned about the CHTS, that looks like a real pain to change. The coil thing sounds possible except that it hasn't been all that warm recently. If this was another car without all of the engine electronics I would definitely think coil but I just don't know the Z electronics well enough to make that call. I'm using the Z as a daily driver to keep miles off the lease G37 so maybe this will pop up again and I can troubleshoot more fully. If anyone has any additional ideas I'm all ears.

rogerz

you can at least get an ohm reading on the chts by pulling apart the oval connector usually found on top the engine right side. It isn't hard to replace just tedious as you need to take a few pieces of tin etc off. If you do replace it is in a dry hole so don't button it down hard snug is plenty just want good contact with block. do a google on it there used to be a procedure listed somewhere.

Defender405

My starting issue is more consistent now, seems to do it mostly when warm but not hot and also on some cold starts. It always acts flooded when it doesn't start and pulling the fuel pump fuse to get it to start has worked every time so far to get it going. My fuel pressure is OK via the FSM at
30 +/- PSI, I haven't got a chance to OHM out the CHTS yet. In looking at the fuel system diagram it looks like the FPR is in line and could cause the ring to overpressure and dump excess gas and "flood" the cylinders. Does this sound like a possible cause or still a likely CHTS thing? Is there an easy way to see if the FPR is doing its job short of disconnecting the return line and seeing if gas comes out? I Will OHM out the CHTS tonight or tomorrow and report back.

Defender405

Checked out CHTS by FSM and it looks OK, voltage rise is good and resistance is fine. The funny thing is after I checked all of this it quit having the problem and has been trouble free for a few days now. The only other thing I did was to remove and replace the vac line to the FPR. Unfortunately I did all of this at the same time so I'm not sure if it was the vac line or a loose connection on the CHTS that helped. Obviously these cars are vacuum crazy, but could a loose vac line on the FPR cause what I have been experiencing? Seems like a possibility, no?

masterhufflpuff

Yes that is a very high possibility. Any sort of vacuum leak on these cars make a large difference. Glad you got it sorted out, enjoy the Z!

Defender405

I have changed all of the HVAC vac lines, I guess its time to change the others too. This is new for me. I'm a Brit car guy usually, and there isn't one damned vac line on an MG. Learning new things every day.