Hard engine miss

[Ryders300zcar]

Wanted to see If anyone had suggestions as to what to check next. Very hard engine miss. As you rev it up to 2000 rpms it really gets heavy. The miss is harder than you would expect from one cylinder. Strong enough miss that the car is not drivable. Seems if the entire engine is losing spark or fuel. Only code showing is 42 which is fuel temp sensor. Connected or disconnected makes no difference. Read that it should not cause much of a problem. Put in new plugs, compression is 170 to 180. Timing is 15 degrees. All fuel injectors clicking with the cas check method and the screwdriver to ear: ohm tested to 10 to 15. All coil packs firing (ohm tested most within specs, a couple slightly off no more than a couple of points. Shutting down cylinders 1 at a time makes no detectable difference at idle or at higher RPMS. Only thing I have found so far not testing within spec is the mass air flow sensor. I get readings way over the .8 to 1.8. Unplugging it makes no difference at all in the way it runs. Could that cause that much confusion. Would like some suggestions from someone more knowledgeable. Seems like this is an over engineered car.

[nissanfreak12]

What are the actual numbers on the injectors? You said 10-15 ohms, they should be between 10-14ohms no more no less.

[Ryders300zcar]

1 ohmed at 15.6. And the plugs that I removed were black and sooty which seemed to indicate rich mixture. The others were within range.

[Ryders300zcar]

And again, this miss seems far stronger than just 1 cylinder. And all of the plugs were sooty.

[nissanfreak12]

That one is bad. How were the other ones? If they were 14.1+ they are also bad. If they are 13.7, basically they will be bad shortly. I would look into new injectors, new style are a better choice because they handle ethanol better than the old style.

[Ryders300zcar]

You may be right. I did replace all six about 3 years ago but they could be the problem. I just did not think that 1 being bad would cause that much trouble. I can barely get it above 2000 rpms it is cutting out so bad. I will probably just for fun try replacing the mass air flow sensor since that will be so easy and will at least eliminate that since it seems suspicious. Thanks

[nissanfreak12]

Don't throw money at it, if the MAF is bad or a little bad it will have a code in the ECU unless it is not a N62 MAF, then yes that could be an issue. But injectors will create all kinds of havoc with a car running properly, it is what makes the car go.

[DCaff300ZX]

Don't throw money at it, if the MAF is bad or a little bad it will have a code in the ECU unless it is not a N62 MAF, then yes that could be an issue. But injectors will create all kinds of havoc with a car running properly, it is what makes the car go.

Second this sentiment, and completely agreed...the MAF reading and testing doesn't sound right as it should barely run without MAF, and as mentioned the injectors are sensitive to ohm reading and at least one is bad and will cause what you mention- I had the same issue in my '90 NA which became worst when two went bad, no start/run period.
You have a lot of testing and such to do (and possibly service replacement) what with corrosion, old injectors/connectors/harness, and other connectors/sensors which all will be ready to fail at the same time due to the crappy connectors and age.

[Ryders300zcar]

Thanks for the help guys, I will continue testing and contemplate pulling that plenum off again.

[Ryders300zcar]

To update on my progress. Since the readings on the MAF were so crazy, and the post above that said it should barely run w/o one, which is what it did, I bought a cheap one on Amazon just to satisfy my curiosity. And it now runs like a striped a**. It fixed the lack of power problem but now it doesn't want to idle whereas before it would idle all day. The new MAF only has 4 connector prongs while the original had five. I read on another post somewhere that the early 90 models all had 5 prong connections while some later ones only had 4 and that this could be the reason for the no idle problem. Does this make sense to any one?

The voltage reading on the old one were so crazy I didn't list them as I did not believe them myself. I got 35 or so volts from the b or signal wire to ground. I don't know how you get that from a 12 volt system. And with the new one I get about .5 or so with the ignition on and not warmed up. Closer to FSM. And I got the crazy readings on more that 1 meter on auto ranging and on DC.

Any thoughts?

[DCaff300ZX]

You will need the correct N62 MAF for correct operation, as you have found...no alternatives to my knowledge.