1991 Q45 runs rough-replaced MAF, fuel injector still cant get compression

[q45freak1991]

THE CAR STALLS ON THE HGHWAY BUT STARTS BACK UP, RPMs GO CRAZY H MECHANIC DOESNT KNO ANYTHING ON HOW TO FIX IT. I TALKED TO A INFINITI MECHANIC HE SAID THE ECU COULDNT BE READ SO I REPLACED THAT HE THEN TOLD ME IT COULD BE THE FUEL INJECTOR OF THAT CYLINDER OR AIR FLOW SENSOR, REPLACED THOSE AND IT STILL ISNT RUNNING GOOD...IT CUTS OFF WHILE DRIVING, ROUGH STARTS, SHUTS OFF WHEN I STOP SHORT.. SOMETIMES I CANT DRIVE PASS 3000 RPMs REPLACED THE STARTER AND GOT A OIL CHANGE AND STILL ISNT RIGHT ANY SUGGESTIONS???

THANKS

[goody90q45]

Welcome to NICO. You've come to the right place for help. There's a wealth of information here and at Q45.org. Read, read, read and you will soon begin to see that you're Q is not as complicated as it seems and the problems you're currently having are probably quite simple to remedy. The next time you go see your mechanic you should be able to tell him what and how to check rather than the other way around. The following are some simple DIY's that every Q owner/NICO member should be able to do or teach themselves to do.

THE CAR STALLS ON THE HIGHWAY BUT STARTS BACK UP, RPMs GO CRAZY

These sound like typical MAF problems but since you've already replaced the MAF try checking the connector. It should be free of corrosion (use a toothbrush and 3 in 1 or PB Blaster to clean it) and after 15+ years the pins will need to be tightened. Use a pick or small nail to adjust the pins to match the center one in the pic I posted. When you're done it should fit tightly on the MAF and not be able to wiggle up and down. Another common problem is bad wires in the connector. Many owners have had to replace the MAF plug but try cleaning and tightening it first.

....... HE SAID THE ECU COULDNT BE READ SO I REPLACED THAT. HE THEN TOLD ME IT COULD BE THE FUEL INJECTOR OF THAT CYLINDER OR AIR FLOW SENSOR, REPLACED THOSE AND IT STILL ISNT RUNNING GOOD...

Are you getting the check engine light (CEL)? Since its pre-96, it's OBD-1 so your mechanic may not have been able to read the ECU codes with the diagnostic equipment in his shop. The ECU is in the passenger front footwell and the codes can easily be read. Since you've already replaced the ECU you know how to remove it. Before you remove it check to see that the long blue connector is seated flush to the ECU. It's easy to get this in a bit sideways when bolting it in and all the pins will not make good contact. Follow the steps in this thread from Q45.org to read the codes. Let us know what codes are there.

zerothread?id=60332

Just for kicks, if you own a voltmeter try ohming your injectors and while you're there, the knock sensors. Neither is probably related to the problem your having but it only takes 5 minutes and along with pulling the ECU codes will tell you a lot about how your engine is running. The bundle of connectors you're looking for is at the end of the plenum (intake manifold) on the passenger side of the engine.



Try doing these few things and I bet you'll see some improvement. Hopefully it's just a loose, corroded MAF connector. Let us know what you find.

[maxnix]

Sounds possibly like some loose vacuum lines to me. Difficult to read so I am not sure what poster's intent is.

Please do lose the CAPS KEY as not doing so is considered SHOUTING.

Thank you.

[Q451990]

Wow Mike, that's the most complete reply I have seen in a while!

Heath

[goody90q45]

Wow Mike, that's the most complete reply I have seen in a while! Heath

I went to Starbucks a little late last night.

[Q45denver]

You should take it to a dealer or at least someone that can can hook it up to a Nissan Consult.