Needs Some Advice, Please

[Cal Learner]

Wife's 1990 Maxima GXE has recently developed a misfire/rough running condition after 133,000 miles. Until now, that 3.0L V6 has been a beautiful motor, and she's looking to get it back that way. Here's what's just been done within the past 30 days by our usually reliable indy:

1) all new injectors2) new coolant temp sensor3) new battery

Problem began last month with stumbling engine at all speeds. CEL on. Indy pulled code 51, injector circuit problem. Further diagnosis pointed to cyl 5 injector. While the intake manifold was off, we had him replace all six injectors with new OEM parts. For about one week, car ran fine. Then, one morning the car cranked long before starting and ran rough at all engine speeds, so back to the indy. This time, code 13, CTS. Replaced CTS with new OEM part (and new battery). No improvement. Further diagnosis led indy to suspect that now the new injector at cyl 3 was bad, altho there was no code set for bad injector. Indy replaced injector 3 with new one and the car appeared to my wife to run OK. Next morning, I tried it myself and it starts right up as it should and idled alright until the rpms dropped down to normal range, and then it was clear that there was intermittent misfire. I drove the car around the neighborhood. It runs alright on gentle acceleration and at neighborhood speeds (30 mph). But when I give it WOT, the engine seems to nearly stall out when the kickdown engages. Tach drops way down, and the engine just seems to stall until I let up on the accelerator, then the engine may either quit, or it may return to idle rpms. Each time I go WOT, the CEL comes on, but goes out again when I apply gentle accelerator pressure. That's where it stands today. Wife is going back to the indy today, but she could sure use some suggestions from knowledgeable Nissan DIYers. TIA

[MinisterofDOOM]

Welcome to NICO!

Definitely don't rule out any potentials just because you're not seeing codes for it. Remember that OBDI was not as comprehensive as OBDII, so a lot of things can be wrong without tripping codes, and even when codes do show they're not as specific.

When was the last time ignition components were replaced? Cap, rotor, plugs, wires... What plugs were used? Make sure the rotor is adjusted to be in time.

If your indy mechanic suspects the new injectors, have him test them with an ohmmeter. Good injectors will read between 12 and 14 ohms.

I would also check the fuel pump. If you are having a fuel issue and the injectors check out, fuel pump and filter are the next likely culprits.

[coolhand]

Also, try to replace the Mass Air Flow sensor with a know good used one.I had the same problem with my 89 and that could be faulty.

[Cal Learner]

Thanks gentlemen for your input. With injectors and CTS replaced, and coil, ignition wires, plugs, distributor/rotor checked out as good, it turned out to be a bad MAF sensor. She purrs once again, and so does the wife!

[NutriaforBreakfast]

Sounds exactly like the problems I had with my MAF