'92 Q45 cylinder #6-no spark

[Lou92Q]

My '92 Q45 is not getting spark on cylinder #6. Plug is good. Coil is good. Replaced the distributor transistor for that bank of cylinders. Replaced the connector that plugs into the coil for that cylinder coming from the distributor transistor. We can measure a pulse coming to the #6 coil from the distributor transistor but no spark. Have no idea even what to check next. Also, that cylinder (and no other) has a resistor coming off the coil wire to a ground on the engine near the oil filler cap. Took the resistor out of the loop, no change. Checked the resistor and read resistance. Don't know what it's supposed to read exactly but it's not wide-open or dead shorted, so I'm thinking it's OK. Does anybody know what this resistor is for and could it have something to do with the problem? Out of tricks. Any advice would be appreciated.

[EdBwoy]

Last time I dealt with a car with only one bad cylinder, it turned out to be ECU-related. Everything was correct, but the computer wasn't outputting signal to the coilpacks.

Now, I don't want to predict gloom for your situation, but I'm also not familiar enough with this platform to say it'sa simple fix. Can you post pictures of this resistor to help me visualize where things are?

[Lou92Q]

Cylinder #6 shown with resistor and cable grounded to engine under oil filler cap

Coil harness, distributor transistor & cylinder #6 shown with resistor and cable grounded to engine under oil filler cap. Hard to see, I know.

FYI, I went ahead and ordered a used ECU to see if that will fix the problem.

Thanks for any advice you can provide.

[Lou92Q]

Replaced the ECU. Problem solved. Thanks, EdBwoy!

[EdBwoy]

You're welcome Lou, and thanks for the update! All is well that ends well.
I'll mark the topic as solved, for posterity.

[Lou92Q]

Spoke too soon. ECU didn't fix the problem. Car ran fine for about 3 or 4 days then began to get hard to start after warming up. Now, missing and spitting our bluish-white smoke again. I'm out of ideas.

[Q451990]

Are these the same symptoms as you were experiencing before?

If not, my next steps would be to start looking for fuel related issues... Fuel pressure bleed down (bad injector o-rings or another leak in the system), A bad fuel pressure control unit, fuel pressure out of specification - etc.

[EdBwoy]

CTRL + Z, CTRL + Z!!
I've edited the title again, to not say that the issue has been solved.

That hard to start when warm phenomenon reminds me of an idle air speed issue in newer cars, after major engine work (Either replacing the throttle body, IACV, or I'd argue replacing the ECM too).

Although it does seem like your main/prior issue was sorted out. Does it seem specific to any cylinder this time?

[Lou92Q]

The problem is the same. Missing on at least one cylinder. Not sure yet whether it's #6 as I haven't had a chance to look at it. I'm almost positive that it's not fuel related. Injectors only have about 25K miles on them and they checked out good 2 or 3 weeks ago. I replaced the MAF about 10K miles ago but with an inexpensive after-market unit ($80.00 or so, I think). Could it possibly be that again? It's acting exactly like it did when the MAF was bad before.

[Q451990]

Aftermarket MAF sensors have had a lot of issues. Back when our cars were newer, and popular - T3 in Atlanta tried multiple aftermarket and remanufactured MAF vendors, and could never find one that was reliable enough to continue using in customer cars.

[Lou92Q]

Thanks for that. I suspected as much. I'm on my third MAF sensor. The factory original lasted 120K and I've gone through two more between then and 150K, so that makes me suspicious from the "get go". Maybe I should shell out $300.00-$400.00 for a Bosch? Can I even get one from Nissan at this point? Guess I could call the guys in Scottsdale and find out?

[Q451990]

Factory part is $569.72 (MSRP 730.42) from www.orderinfinitiparts.com! The Bosch 63109 is available at Rock Auto for $188.79, so that would be tempting.

From some of the old Q45Tech posts, it was his opinion that there's a big difference between Bosch of Japan, and other divisions of Bosch. The original was made by JECS (Japan Engine Control Systems) that is/was a joint venture between Nissan and Bosch of Japan.

If idle fluctuates when you lightly tap the black box on your OEM MAF, it's likely that the solder connections between the three terminals that feed the circuit board from the connector have a cold solder joint. I've had some success re-soldering them. You just need to scrape away the bead of silicone sealant, and you can remove the black cover from the sensor and access the board. My symptom would be a "bump" at idle sometimes... almost like someone lightly rear ended me. Your symptoms sound different, but if you still have your old sensor, it wouldn't help to remove that cover and see if those connections look discolored from overheating.

[Lou92Q]

Thanks for the advice q451990. I went for the Bosch MAF sensor from Rock Auto. It's not "re-built", so hopefully I'll have better luck this time. BTW, I drove the car for about 15 minutes today and it started right up and ran perfectly. Very frustrating.