Need some help with a 94Q

[nismotuner82]

I have done a lot of searching the past few days on a particular car (q45) I have in my shop. Q first came in with a mis-fire/loading up sensation. The loading up was cause by the fuel pump, as she was failing, and was the original pump. Replaced pump, and now have power, but still a mis-fire. Replaced the following for rough idle:

All 8 coil packsall 8 plugsFuel filterInduction service with seafoam in the tank as wellMAS clean with brake cleaner from a distanceMAS harness inspectionNo SES lightDrained fuel, and put fresh 93 octane into the tank

This does not matter if its hot or cold (engine), or ambient temp. outside. Feels like a mis-fire/dieseling effect at idle, and is worst with a load(in gear, a/c on ect.) I am lost, and looking to my fellow tech/nico member for some help. Before you nazi's ride me about using the SEARCH, please spare me.......I have searched for the past 3 nights.

Thanks in advance,

Cory

[goody90q45]

No CEL and a crummy running engine usually means fuel supply issues. Depending on how long the FP was going bad it may have taken out the FP Control Unit. Try running a jumper from the FPCU connector to the chassis which will run the fuel pump on high speed only. If this solves your problems it's the FPCU.

[nismotuner82]

Ok so ground the terminal with the gator clip in the photo? I am just trying to be correct with what wire i am grounding. Thanks for the quick reply.

edit:

A side note:the car clears up if i start going down the road.....just food for thought.

Cory
Modified by nismotuner82 at 4:40 AM 9/17/2009

[Infinitiguy19]

Ground it on a unpainted surface on the sun deck.

What RPM's does the stumble disappear at?

I think I have the same problem as you and I am currently think its electrical or just dirty intake/fuel system.

I plan on cleaning the EGR again as well as the EGR port

BG flushing the fuel injectors

Replacing the Throttle Body with a 1990-1992 one (grey TCS motor) .

And if I have to replace the plenum with my spare if its that bad.

[goody90q45]

Ok so ground the terminal with the gator clip in the photo?.....A side note: the car clears up if i start going down the road.....just food for thought......

Correct. Jumper from the pin with the alligator clip to ground.

How does she pull going up a hill or accelerating hard? The jumper to ground is free and only takes of couple of minutes. Might as well do this first and rule out a bad FPCU.

Have you ohmed the injectors and KS? Pulled ECU codes?

[nismotuner82]

I have not ohmed the injector's, or the KS for resistance, and there is no SES light. In Florida, we don't have a whole lot of hills to go up, but flat out on a straight she does not pull good until 4k RPM. I have been told that im used to my old ls1 powered car by most, so my butt dyno could be askew slightly. Might have some spark knock until that point, but afterwords it seems to clear. The rough idle seems to disappear at or about 1k rpm at idle to answer a previous post.

Cory
Modified by nismotuner82 at 3:35 AM 9/18/2009

[elwesso]

if you replaced your fuel pump and still have a misfire the next step is to check the injectors.. If the car is running chances are the FPCU is fine because if it was burnt out it wouldnt operate the pump at all..

My guess is you have 1 or 2 bad injectors.

[JOSHIE88]

yup i was thinkin injectors. i have a 94 and sounds like what my car used to do

[nismotuner82]

Ok so I took everyone's advise and here are the results. Nothing changed with the fuel computer wire grounded. As far as ohming the injectors, I did everything that was said to do with ohming them and I had no results from doing this. Before you ask I have a fluke DVOM tha I use everyday. Unhooked the battery, found the injector harness, red lead on battery, black lead on injector pins......nothing. Same for the KS.....nothing. What am I doing wrong here guys?

Thanks in advance....Cory

[goody90q45]

Unhooking the battery doesn't sound right.

[Q451990]

Check between the positive battery terminal with the wire still connected - and make sure the ignition switch is in the "on" position. The injectors are on a switched circuit after 1994.

Heath

[nismotuner82]

I will check it again on Monday. Thanks all.

Cory

[mxr662]

http://q45.org/ohminjectors.html

[nismotuner82]

Ohmed the injectors, and they all came out around 15.0 with the key in the run position. The KS's was weird with the key off one was .530, and the other would climb/drop depending on how it felt from .330, to 1.08. Feedback would be helpful.

Cory

[Q45tech]

Replace both KS and the KS harness. Also replace the battery in your VOM as it is obviouly weak [15 ohm reading].

[nismotuner82]

Thank you for the quick reply. I will give that a shot.

[elwesso]

actually the 15 ohm reading was most likely from the key being on. while doing this test, the key needs to be OFF with all doors and such closed..

replacing the KS will help with getting about 50HP back, but it wont help with the rough idle.. I might look around for a vacuum leak, is there any other service history that you know of?

[nismotuner82]

No I do not have any other info on the car. The car was bought at a local auto auction for resale for a car lot, so I am trying to get it correct for the owner. I have to admit that I do like the car quite a bit now....

Cory

[Q451990]

actually the 15 ohm reading was most likely from the key being on. while doing this test, the key needs to be OFF with all doors and such closed

Didn't we determine that some of the later Q's (thought the change was in '94 but maybe it's later?) have their injectors on a switched circuit - and therefore the key needs to be on?

Heath

[Q451990]

From reviewing the service manuals - it appears that the injector circuit moved to a switched circuit for the 1995 model year.

Heath

[Q45tech]

Why you just read injectors at the harness connector and skip all the confusion.

[Q451990]

True. Using the positive 12V connector that feeds the injectors would bypass everything and should yield more accurate readings. It's connector is labeled S51 in the FSM.

From a practical standpoint, it's easier to poke the positive lead of the meter into the positive terminal of the battery between the connector and the post rather than trying to hold it on to the pin in the connector while using the other lead to probe the other terminals. Maybe I should invest in a set of very small aligator clips.

Heath

[nismotuner82]

So I took the advise of ohming the injector's once more with all doors closed, and the key off. All read 10.6-11.8 ohm's except the #7 injector. That came up with 75 ohm's, so I am sure I found the culprit. So it looks like I will be removing the intake manifold, and was curious as to what needs to be replace or rerouted with this procedure?

Cory

[Q451990]

So I took the advise of ohming the injector's once more with all doors closed, and the key off. All read 10.6-11.8 ohm's except the #7 injector. That came up with 75 ohm's, so I am sure I found the culprit. So it looks like I will be removing the intake manifold, and was curious as to what needs to be replace or rerouted with this procedure?

Cory

Cory,

Although 75 ohms is out of spec - in my experience the injectors continue to function in a way that doesn't show a noticable miss well into the 200+ ohm range. Typically the "injector death bounce" (dead miss) shows up only after they open.

Of course injectors can ohm good and still not function if they're clogged. I think I would try a pressurized injector/rail flush if you think that's a possibility.

Heath