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I know, don't touch them!

 

Trying to finish up a customer's '93 Allante. The car had been sitting for about 6 years at another shop. Went through the engine to repair the usual pulled head bolt threads and failed head gasket, back together and in the car. Cylinder #1 has a constant misfire.

 

1. Checked codes, none.

2. Checked for missing cylinder by lifting spark plug wire up off coil, #1 is the culprit

3. Exchange positions of spark plugs (new NGK) and wires, no change.

4. Check companion cylinder (two wires per coil), firing. Swap posts, no change.

5. Check compression even though I knew it was good and it is.

6. Suspect injector. Try to use on-board diagnostics (very comprehensive, just like GM scanner!) to do injector actuation test with fuel line pressure drop, check valve in fuel pump sticky and won't hold pressure. Pull injectors for testing, showed no problems but got them cleaned anyway.

7. Reinstall injectors in different order, no change. (Edit: or so I thought. I didn't number them so when I put them back in random order I apparently got #1 back in the same hole. Read to the end of the thread)

8. Check for vacuum leak around intake, find a hole in the #1 runner of the phenolic spacer under the intake manifold. Remove intake and spacer, repair with epoxy and reinstall. No change.

9. Try injector actuation test, this time the pump holds pressure. Each injector shows about 20 psi drop from 43 psi, shows that the wiring to each injector is good and that the ECU is commanding each injector.

10. Do power balance check by shutting down each injector while engine is running and noting rpm drop. #1 has no effect on idle speed, all others drop 50-75 rpm (digital readout increments are 25 rpm) 

11. Pull spark plug, looks wet. Check spark again by putting new plug on top of engine with #1 plug wire connected, sparking, try different plug, different wire, install spare ICM with coils from another Northstar, no change. 

12. Perform power balance check again, still no change in idle rpm with #1 injector shut off, all others have rpm drop.

 

I'm thinking that my next step is to go through the connectors and look for an open or poor connection in the injector or ICM harness.  I'm also going to go through all the engine parameters via PCM data and record those to see if there are any anomalies. Thoughts?

 

 

Edited by mender
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3 hours ago, mender said:

Thoughts?

Basic question, ok you have switched coils/icm(never seen a bad caddy icm) but I have to ask, have you seen the injector pulse with a noid or test light while engine is running?

also

Please rotate coils putting that #1 in another location and please try another plug wire.

also

are you able to generate a injector open code? (ecu is pretty basic)

 

Sorry I know you the basics but gotta start somewhere...

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1 hour ago, Team Infiniti said:

1. Basic question, ok you have switched coils/icm(never seen a bad caddy icm) but I have to ask, have you seen the injector pulse with a noid or test light while engine is running?

also

2. Please rotate coils putting that #1 in another location and please try another plug wire.

also

3. are you able to generate a injector open code? (ecu is pretty basic)

 

Sorry I know you the basics but gotta start somewhere...

1. Can't do a running noid test, the injectors are inside a sealed manifold. Can and have shut down each injector while engine is running (see #10) and have verified injector actuation (see #9) via the on-board diagnostic capability.

2. Plug wires have been switched and tested for resistance, no change (see #3, #4 and #11). Coils are wasted spark so fire two cylinders, associated (cylinder #4) works well. I've had a DIS coil that had a dead post, not the case here. Spare ICM had coils attached. Checked connectors, all look good. Spark seems good when connected to spare spark plug and grounded.

3. PCM is actually very comprehensive but OBD1 so no cylinder misfire codes. Not sure what you're after with an injector open code. All injectors test 12.8-13.0 ohms for resistance, show 12.25 volts at the connector so power source is good. Will be checking circuit to PCM terminals, will see if I can back probe #1 to verify that the PCM is grounding the circuit.

 

The factory shop manual is about 4 inches thick and is not user friendly. I've gone through the diagnostic trees and about all that's left is the PCM check/replacement.

 

More symptoms: #1 is still off-line but #8 is now having issues, cutting in and out. Engine will now backfire once upon quick throttle application off-idle but not under steady throttle. 

 

Some car history: the owner bought the car remotely (Florida), shipped here, received the car and attempted to drive it to another town 10 miles away and the car promptly overheated. He took it to another shop where they diagnosed the headgasket issue and replaced the starter (shop is now closed down so I can't get more info). Car was then stored for six years until the owner sold his building and now wants to drive it. In other words, it sounds like this car had numerous problems before I inherited it.

Edited by mender
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 Picking up dinner right now, will continue when back to laptop.

 It's been years since laying hands on one but used to be well-versed in this management system, weak spark from one post is a very common failure mode of ignition coil,  swapping coils around on the ICM was GMs diagnostic  suggestion, I use a grounded test light to verify an inch plus of  strong lightning from each post.

 

 

Edited by Team Infiniti
see below
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The injector firing while running is next on the list. Given the sequence of testing with the actuation test before further tests that lead to the PCM, it sounds like the actuation test isn't a guarantee that the PCM is controlling #1.   

 

It wasn't backfiring with only #1 out but I agree, ignition for #8  is indicated. The spark from both posts of the 1/4 coil is white and bright and is close to 1 inch before it finds a different path.

 

The intake is the cast aluminum bathtub with the sealed lid, no backfire door. I have a later plastic intake with the door in my excess parts storage but it's a MAF type.

Edited by mender
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6 hours ago, mender said:

11. Pull spark plug, looks wet

 

6 hours ago, mender said:

been sitting for about 6 years

Edited, forget spark or injector issues

 

FPR is under the intake, how about a ruptured diaphragm flooding #1? Early design bathtub?Look into possible intake cracking.

Edited by Team Infiniti
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On 5/24/2018 at 9:20 PM, Team Infiniti said:

 

Edited, forget spark or injector issues

 

FPR is under the intake, how about a ruptured diaphragm flooding #1? Early design bathtub?Look into possible intake cracking.

Plug is wet looking, not soaked. Can't get it to light (Edit: was oil film from cylinder not firing). FPR is at other end of intake and system holds pressure, so not ruptured diaphragm. Intake not cracked, had it off for a good look.

Edited by mender
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Completed:

1. Replaced NGK plugs with AC-Delco.

2. Replaced coil cassette and plug wire set with used parts from a '93 STS that I scrounged this weekend. 1/2 price sale at the boneyard so I picked up the PCM as well, not installed yet. (Edit: #8 cylinder back online, ignition parts took care of that so one problem solved)

3. Backprobed injectors, all have power and are grounding.

4. Did a leak-down check on #1, 8%, verifies compression test.

5. Sprayed MAF sensor cleaner around the #1 intake runner area while running, no change, liquid sat there.

6. Listened with a hose around same area that had the hole that I repaired, no hissing.

8. Swapped known good coil into 1/4 position, no change

 

#1 continues to be dead at idle and on test drive.

 

1. If it's a vacuum leak it should cut in under full throttle; poor cylinder pressure due to leakage should still cut in above 2500 rpm or so. No change regardless of throttle position or rpm.

2. Cams are reground, lifters are NOS. Slight tapping from the valve train but not slapping as if parts had lots of clearance. Again, no change regardless of throttle and/or rpm.

3. Compression test showed normal numbers and was same as the others so valve actuation is good enough to run.

4. Cam timing is good as the other 7 cylinders are running well and producing power.

 

Electrical tests on #1 injector:

1. 12.8 ohms resistance across leads to injector

2. 12.25 volts through harness to PCM connector with key on (battery voltage).

3. Backprobe of connector from PCM while running shows flashing light of the same intensity as the running cylinders

4. Individual injector actuation through PCM diagnostics works for all 8 injectors.

5. Power balance check via PCM diagnostics cuts injector signals and results in an rpm drop on the other 7 injectors.

 

Can't access injector directly to check for clicking while running because of sealed plenum, tempted to pull off lid and crank it while checking. Should be too lean to start as it will act like wide open throttle but with only start-up pulse width. I'll plug in the other ECU since I have it.

 

Update:

1. Plugged in other PCM, no change in running but now have an engine overheat code - that went away when I went back to the original PCM

2. Managed to enlist my wife's help to have her crank the engine while I checked for injector clicking. Pulled the top cover off for access, fuel pump relays, bled the lines but it still tried to start and run. No clicking from #1 but clicking from #3 and #5.

3. Probed wires while cranking, signals are there.

4. Removed injector and used an old injector plug and a battery to power the injector. No clicking.

5. Tested #3 injector same way, clicking.

6. Put #3 injector in #1 hole and a spare injector with the wrong tip but right length and plug into #3 hole.

 

That's where I had to leave it, will get back to it on Wednesday but I think I'm on the way. So much easier when the injectors are accessible. May not be over yet, I had a one in eight chance of getting the faulty injector back in the same hole but as they say, if it wasn't for bad luck, I wouldn't have any luck at all.

 

Interesting that the injector actuation worked just fine as did the injector cleaning, resistance tests, etc. but no function when running.

 

 

 

 

 

Edited by mender
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Had it in the back of my head you got a dud injector back in the same hole, but figured no way it could get you like it did me...  (the one and only time this has ever happened)

 

Backstory:

Bought running but neglected infiniti to get all swap elements all at once, it was hitting on 6cyl for the 2.5 hr trip home from purchase, before pulling engine it was decided to drive, gain experience, lay hands upon and and fix all codes. Melted knock sensors, a few injectors, unneeded plumbing, tune up and various other things to get fixed, not (yet) having a stockpile of v8 infiniti junk, I was off to ebay to shop the hell out of these expensive parts...

 

Proud that I was mastering over-complicated OBD1 antique infinitis, (jap equivalent of northstar) it fired rightup it ran perfect for 5 seconds then cyl 4 dropped out (was a dead miss when this all started)

Drove me nuts till it was figured out that not all new $28 injectors are good, it just happened that I replaced one with a bad coil with another that had a manftr. defect in the pintle.

 

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Couldn't wait, got home this evening and had my wife help again, clicking from all injectors, reassembled, plugged in the fuel relays and brought it back to life: success! All eight cylinders, finally!

 

I was going to buy new injectors; with my luck I would have had the same result!

 

This just proves that education by whatever means is still expensive. Can't charge the customer for the time it took.

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12 minutes ago, mender said:

Couldn't wait, got home this evening and had my wife help again, clicking from all injectors, reassembled, plugged in the fuel relays and brought it back to life: success! All eight cylinders, finally!

 

I was going to buy new injectors; with my luck I would have had the same result!

 

This just proves that education by whatever means is still expensive. Can't charge the customer for the time it took.

So what was the problem?

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#1 injector was dead.

 

Frustrating because it worked for the actuation test (run fuel pump to get pressure then note pressure drop when the injector is actuated) and the testing/cleaning of the entire set. I purposely put the injectors back in a random order afterward but it appears that I managed to get the bad one back in the #1 hole, making it seem unlikely to be a specific injector.

 

I'm still going to watch that cylinder just in case. ;)

Edited by mender
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6 minutes ago, mender said:

#1 injector was dead.

 

Frustrating because it worked for the actuation test (run fuel pump to get pressure then note pressure drop when the injector is actuated) and the testing/cleaning of the entire set. I purposely put the injectors back in a random order afterward but it appears that I managed to get the bad one back in the #1 hole, making it seem unlikely to be a specific injector.

 

I'm still going to watch that cylinder just in case. ;)

 

That makes sense now. I thought you just swapped two injectors and the problem stayed with the cylinder.

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