HELLLPPP!!! IS IT MAF? OR FUEL PUMP???

[Q45phill]

I KEEP reading that the MAF will cause my G50 to buck and sputter at cruising speeds but it idles just great? also my fuel pump is starting to hum loudluy so i know what time it is. but whats causing the bucking and sputtering at 18-2500 rpm? just want to make sure i fix it right, its a wonderful car...1990 q45 with 150211 chain guides replaced, top end rebuilt in 07 bottom end rebuilt in 08 ....soooo

[qship96]

Top end rebuilt in 07, bottom in 08??? whats up with that strange sequence of repairs????

Your problem could be anything- start with new fuelpump, since it is humming it needs to be replaced. Could be fuel pump control unit, maf, throttlebody sensor, etc causing your problem- check codes and report back.

[Q45phill]

thanks qship i really appreciate it...how do i check codes on this car? i'm familiar with alot of OBD 1 AND 2 american cars and how to check? also would or could a fuel pump alone do this or would it be a combination of both?

Top end rebuilt in 07, bottom in 08??? whats up with that strange sequence of repairs????

Your problem could be anything- start with new fuelpump, since it is humming it needs to be replaced. Could be fuel pump control unit, maf, throttlebody sensor, etc causing your problem- check codes and report back.

Top end rebuilt in 07, bottom in 08??? whats up with that strange sequence of repairs????oops sorry not the best at posting...yet Your problem could be anything- start with new fuelpump, since it is humming it needs to be replaced. Could be fuel pump control unit, maf, throttlebody sensor, etc causing your problem- check codes and report back.

[maxnix]

You replaced Valves, Guides and HLA? Why?

Oversize bearings on the bottom end? Why?

New Tensionsers?

Your fuel pump is toast, so replace it, O ring and fuel filter before it takes out the expensive FPCU also.


Modified by maxnix at 10:31 PM 3/8/2009

[goody90q45]

...how do i check codes on this car?......also would or could a fuel pump alone do this or would it be a combination of both?

ECU is behind the passenger side footwell. Look for a 1" carpet square covering a 10mm nut.

Is your CEL illuminated? If not, chances are pretty good it's the fuel pump/FPCU.

These instructions from Q45.org will get you through pulling the ECU codes.

zerothread?id=60332

[Q45phill]

THANKS MIKE AND MAXNIX, the engine work was all done by previous owner, he owned a garage and it was his personal vehicle, i havw all the paper work and reciepts, anyway, i am replacing the fuel pump ASAP but there are no CEL on at all,but i'm goning to acess and check the ECU anyway...thanks again...

[Q45phill]

UPDATE didnt get to ecu yet!!! but started on fuel pump and found screws stripprd out, no o-ring, and different length screws half-way holding in the fuel pump...its a mess and apparently this guy was a HACK!!! or just didnt care about the car he drove or who knows what...???? is ...where would i get the correct screws and the o-ring , the pump appears to be new,...just need a good MAF for under $100 bucks now...!!! hint hint any one....

[maxnix]

http://www.infinitipartsusa.com

Additional 7% off sale this week only.

Not confidence inspiring when it comes to his work on the engine.

Fuel pumps are junior high level compared to what he did.

[Infinitiguy19]

Who rebuilt the motor? If it was the mechanic who did the fuel pump, I would just take a shot gun to the motor and start over.

But I wish you luck in finding a tank and if you need the bolts I have those as well as almost ever other bolt that goes to the Q45 sitting in a bag. I also have the tank straps too.

[Q45tech]

Why they make test equipment to read fuel pressure and MAF voltage output vs rpm and air flow. Why they make software to read ecu codes and voltages.

A certified technican is pretty worthless without $10,000 worth of professional test equipment

But with a few dozen gauges, a digital vom, and computer with software you can check a few things.

[Q45phill]

Q45 TECH your funny and correct, i dont have any CEL lights on but i did get a new tank and its very nice!!! clean with no rust or dirt, but i'm still wondering whats the CAUSE of this bucking and sputtering problem between 1800 and 25or 3000 rpm's and could it be a transmission problem. i've NEVER seen a fuel pump do this ...EVER.... so MAF? or FUEL PUMP...and yes i'm going to replace them both any way...just want to be sure...q45tech how would or do i check the MAF with a DVOM?...???

[maxnix]

...q45tech how would or do i check the MAF with a DVOM?...???

To get an answer to technical questions, one must show evidence tht one has read and studied the FSM by being conversant in the techniques suggested therein.

Also read Tangalora's Gold Standard post on the diagnosing and repalecement of the fuel pump and FPCU in IOM, then examine yours closely.