91Q Right Bank Not Running After Plenum Job

Post by **timatt** » Mon Oct 04, 2004 3:52 am

Pulled the plenum and replaced injectors, all hoses, knock sensors and harness. Resealed valve covers. Upon reassembly, engine will run but rough with little power, will not restart when warm. Cold exhaust manifold runners show that entire right (passenger) side is not running. Exhaust smells very rich so I'm thinking ignition problem. Everything appears to be connected properly. ECU check shows code 55. No check engine light when car is running.

Before this job, car ran rough at idle (2 bad injectors) but fine on the road. No CEL.

I'm looking for ideas and advice here. What should I do/check next????

Thanks,

timatt

Post by **duck3986** » Mon Oct 04, 2004 4:35 am

timatt,

how did you identify which two injectors needed to be replaced?

Post by **timatt** » Mon Oct 04, 2004 4:59 am

Ohm Test; One read over 1300 ohm, the other read 26 ohm. I installed 5 new injectors in the locations that are inaccessible without removing the plenum. The other three locations, I used my old injectors that ohm'ed at 12.4 ohm.

Post by **timatt** » Mon Oct 04, 2004 5:04 am

Can someone tell me whether the right bank power transistor is interchangeable with the left bank power transistor? I would like to swap them out to see if the problem folllows.

Also, if I had a bad coil pack (i.e. short or something similar), could it take down all the other coils connected to the same power transistor?

Post by **Q451990** » Mon Oct 04, 2004 5:08 am

timatt wrote:Can someone tell me whether the right bank power transistor is interchangeable with the left bank power transistor? I would like to swap them out to see if the problem folllows.

They're the same.

timatt wrote:Also, if I had a bad coil pack (i.e. short or something similar), could it take down all the other coils connected to the same power transistor?

I suppose it's possible, but not likely - there have been a few coil pack failures, but I haven't heard of them taking out the transistor pack. Definately go back and check your connections... I assume you lubricated the o-rings on the injectors before re-installing? A couple of pinched o-rings could be flooding a cylinder or two on that bank, and preventing adequate flow to the other injectors on that rail.

Heath

Post by **timatt** » Mon Oct 04, 2004 5:29 am

Heath:

Injectors were lubed with silicone spray then pressed straight into the seats, (no twisting). They all seated nicely.

How would a pinched o-ring result in flooding?

also, is there a diagnostic for the power transistor?

Post by **911/Q45** » Mon Oct 04, 2004 5:43 am

Just about has to be a electrical connection that didn't "click in" either injectors or ignition. I would disconnect and reconnect the offending bank's wiring and perhaps use a long screwdriver to listen to the injectors to see if they click while it's running.

Post by **timatt** » Mon Oct 04, 2004 5:57 am

999/q45

I ohmed each injector at the harness connector. All injectors read 13.3 to 13.4 at this connector, so I think that all connections are good.

This afternoon, I will re-check the wiring on the offending bank.

timatt

Post by **Q451990** » Mon Oct 04, 2004 6:20 am

timatt wrote:How would a pinched o-ring result in flooding?

also, is there a diagnostic for the power transistor?

The fuel flows through and around each injector in the rail between the two o-rings. A pinched lower o-ring would allow the pressurized fuel to bypass the injector and dump fuel into the runner. A bad upper o-ring would cause a leak into the engine bay.

There's a test for the transistor pack in the service manual, that you can perform with your multimeter - but in my experience, the results are exactly backwards from what the manual say's you should get. It's been a very long time since I tested one (maybe 1998?) so I don't remember much about it.

Heath

Post by **timatt** » Mon Oct 04, 2004 6:28 am

Heath:

OK, I see you point on the o-rings. I'mn pretty sure I don't have an upper o-ring leak, so if its a lower o-ring leak, would this result in a drop in fuel pressure? I tested fuel pressure yesterday and it seemed normal (i.e. around 42 psig). Also, when I turn the key on (not the starter), the fule pump runs for about 2 seconds, then stops. The system seems to hold pressure after the fuel pump stops. Would that rule out a leak in a lower o-ring??

Thanks,

timatt

Post by **DAEDALUS** » Mon Oct 04, 2004 6:45 am

timatt wrote:Heath:

OK, I see you point on the o-rings. I'mn pretty sure I don't have an upper o-ring leak, so if its a lower o-ring leak, would this result in a drop in fuel pressure? I tested fuel pressure yesterday and it seemed normal (i.e. around 42 psig). Also, when I turn the key on (not the starter), the fule pump runs for about 2 seconds, then stops. The system seems to hold pressure after the fuel pump stops. Would that rule out a leak in a lower o-ring??

Thanks,

timatt

If you're certain it's not dropping pressure even after an hour or two then that's a fairly good sign you don't have an injector leak. Unlikely you would have 4 on one bank big enough to kill the spark. Speaking of which, can you check the spark with an inductive pick-up? I don't know if it would cause what you're seeing, but did you remember to ground the injector harness to the screw just in front of the #2 coil?

Post by **timatt** » Mon Oct 04, 2004 6:54 am

Heath:

Yes, the ground wire was installed. I'm not sure where to put the inductive pick-up. Can you tell me where?

As far as the fuel pressure, I only observed or pressure drop for a couple of minutes after the fuel pump cut off so I can't completely rule out leakiage in a lower o-ring. However, it would seem like the leak, if it exists at all, would be too small to cause flooding of the entire bank of cylinders.

timatt

Post by **duck3986** » Mon Oct 04, 2004 7:31 am

timatt,

could you tell me how you used the ohm metter to test them? Do u disconnect the wire pack and touch the terminals on the injector?

On a digital multimeter, which dial setting do you turn to?

Thanks,Don

Post by **DAEDALUS** » Mon Oct 04, 2004 7:44 am

Take a spark plug wire and run it between the coil and the plug. A single injector leak could not kill more than 1 cylinder.

Post by **Q45tech** » Mon Oct 04, 2004 8:15 am

I can assure you you don't have something plugged in correctly on the valve cover...............careful you might hydrolock or overheat and melt the precats when you finally get it right from all the raw fuel build up.

Common when new techs change spark plugs.

Post by **timatt** » Mon Oct 04, 2004 8:25 am

duck3986

you wrote;***************"could you tell me how you used the ohm metter to test them? Do u disconnect the wire pack and touch the terminals on the injector?

On a digital multimeter, which dial setting do you turn to?"*********************Disconnect the injector wiring harness. Connect one lead of your voltmeter to the positive terminal of your battery, and touch each of the 8 prongs of the connector of the injector harness and take readings for each prong. I don't recall the pinout for this connector to tell you which prong corresponds with which injecotr, but it should be somewhere either in the service manual or the archives.

As far as the dial setting to use, it depends on what settings you have on your meter. You want to measure ohms which may be symbolized on your meter by a greek letter resumbling an upside down U

Post by **timatt** » Mon Oct 04, 2004 9:03 am

Q45tech wrote********************I can assure you you don't have something plugged in correctly on the valve cover...............careful you might hydrolock or overheat and melt the precats when you finally get it right from all the raw fuel build up.

Common when new techs change spark plugs.******************************

Yeah, that would seem evident, but I've checked several times. Could it be something to do with the CAS?

After spending 17 hours Saturday doing this job, my back and knees don't make me feel like "new tech"!!

Post by **elwesso** » Mon Oct 04, 2004 10:34 am

Duck, i have a writeup how to do it on Q45.org.....

Tim... Sorry to hear that your job didnt go as smooth... However, it sounds EXACTLY like when I didnt plug in my power transistor on the pass side.. It ran like crap, and plugged it in and voila!

It def is electrical..... We should ahve just done the plenum at my place

Post by **Q45tech** » Mon Oct 04, 2004 2:40 pm

Now that everyone has confused you. Have you noticed that you have the two identical connectors plugged in wrong?

One of the upper under plenum connectors is identical with the rearmost ignitor [transistor switch pack] connector.

Both cables are long enough to be cross plugged.

So very common when you don't look closely.

Post by **timatt** » Tue Oct 05, 2004 9:56 am

Success!

I took the right side ignition components apart, but did not notice wrong. I checked the ignition harness for continuity and all was OK. I noticed a little bit of oil in one of the spark plug holes from before we re-sealed the valve cover. The rubber boot had a film of oil on it also. I cleaned that off and reassembled. It started and ran perfectly. The oil was really the only thing that I could find that seemed to be out of the ordinary.

Now I did notice the two similar connectors that Dennis was talking about as I was hooking things back up. They could have been reversed before I took things apart.

Thanks all for the help.

timatt

Post by **911/Q45** » Tue Oct 05, 2004 10:02 am

NICO scores again!

Post by **elwesso** » Tue Oct 05, 2004 10:09 am

WooHOO! Id love to drive your Q again Tim and see how it drives after the jobs you did!

91Q Right Bank Not Running After Plenum Job

91Q Right Bank Not Running After Plenum Job

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