94 Q45 Starts then Stalls after warmed up

[raymorin]

I am a new member and I need some help. I have been reading lots of your posts in the past few days and I am impressed with the quality level of the replies.

I own a 1994 Q45 that I bought new here in the Chicago area. It has 145,000 miles and I have always had the dealer do all the expensive maintenance work on time and as needed.

Last March I noticed the fuel pump had a quite loud HUM all the time, especially with low fuel levels.

While on a trip to Melbourne FL I had the dealer replace the fuel pump. They did not replace the fuel controller, as they said no need to unless the fuel pump crashed and burned it up.

After the repair there was still an occasional hum but at a much lower level.

Then the real problem started up. The car will always start if the engine is cold and run just fine. However when I try to restart the car after it has been shut off for 5 minutes or more and while the engine is still warm, sometimes the car starts, then the rpms go to 200 or so then the car stalls out. Usually I just restart and if I give it some gas to keep the rpms above 1500, it will run fine and not give me another problem till I shut off the car.

The above happened only when I was in warmer weather and only occasionally. Say 1 in 5 times. Lately though, as we have had several days above 55 here it has been happening again and getting worse. In the past if I gave it gas for 30 seconds or so and tried to ease into driving then it would run just fine after I got underway. Now the problem seems more aggressive and it takes several tries to get underway as it wants to stall out on me. Again this is still a hit or miss situation. Under virtually identical conditions it may show this problem 1 in 3 or 4 times.

I spoke with two Infiniti Dealers and they both said we don’t know anything about this problem and if we can’t duplicate it we can’t fix it!

After reading the forums I aggressively wiggled the MAF while at idle with no effect.

I could use some comments on what I should do. I am planning on driving back to Florida next week and I am somewhat nervous about this 1300 mile drive.

I will be stopping at the dealer there that replaced the fuel pump and I could use some ideas on what to fix and why.

Thank you in advance for your help. I really love this car. It makes long trips a pleasure.

[DAEDALUS]

It does sound fuel related. A fuel pressure gauge is so much cheaper than a trip to the dealer, and it probably gives better data in a lot of cases.

[maxnix]

Was the fuel filter changed after the new fuel pump was installed? IF not, do it now! Bet the tank wasn't removed and cleaned, but that's another story.

Look for posts on the FPCU. I think one (Tangaloras?) will state a certain solder joint may more prone to fail intermittently when it is warmed by current passing through it after it has been "weakened" by carrying the excessive loads demanded by a failing pump motor . Resoldering usually will repair it.

Increased ambient temperatures may aggravate this failure mode.

Oh, and welcome to the board, Ray. There's a lot of knowledge to be discovered here.

[stanger]

same exact problem with my 90 q45!!! i changed the pump before the controller got burned out too! but there is a reason that infiniti tells you to replace both at the same time!! after having the same problem i troubleshot it down to a fuel pump controller even though there are no burnt pins like usual.i jumped the white wire to ground and it started right up!! just have to replace the unit now...