Q45 fuel pump modulator

[aaacomp]

Hey guys, I think I know the answer but thought I'd check in here to get some feedback.. Well my 92 Q45 was running down the road with NO Problems and went dead.. Not battery etc, checked hose from fuel pump to injectors no prssure while cranking ,, no blown fuse, fuell pump makes no noise, made the small buzz sound in the morning or when starting for first time of the day. checked relay power and have voltage on the relay,, it makes a click when trying to start eng. So, I believe it's the fuel pump modulator and not the fuel pump.. no burnt connectors anywhere. Got the week end now so I won't be doing anything until Monday. Any past problems on fuel pump or modulator welcomed..

Thanks

[texasoil]

the Q45 fuel pump controller is well known for failure on overloads or low voltage. What the cause is the current lead to the pump is fed from a very small solder joint directly to a printed circuit board. It gets hot, then starts to char, and eventually melts th esolder and -no go.

If you are handy with a soldering iron (electrical printed circuit pencil tip, 25 watt. use only rosin core solder), you can probable resolder the connection. There is another unused connection to the same power supply foil on the board, and you can connect that one to the board, and the conncetor pin to the original one and tripple the current carrying capacity of the tiny OEM one. It is a bad original design.

[aaacomp]

Pulled the controller,,Found two Nec K591 labeled as Q5 and Q6 on pcb.oNE nec K591 dead ,, the other was surrounded by a discoloration.. I also noticed a "numer 92" writtien in Blue ink. Well know at salvage yards to mark. I've replace both NEC semiconductors. Had to patch lead from the worst one since the patch was rasied used 30gasolid wire .. Have correct ohm on leads but still no pwr to fuel pump. Looks like pins 7 and 4 are the positive pins.. 4 is the one with no connections.. I'll try patching 4 over to 7 and check.. .Any more ideas?Thanks .. still have a compete active setup...!

[Q45tech]

The controllers NEVER FAIL IF pumps are changed when they start to go bad!.....begin drawing excess current.

I have same controller and have been on 3rd pump for 34k [245k total].

Why is it too much to ask to change pumps every 100k?

[aaacomp]

Well the car has 183k on it but the eng has 83k ,, From the maintence records the pump was changed at 93k. I also ran the test from the maintance manual on it and it has the correct resistance .. In addition, the pump never made excess humming etc, But, I am inclined to believe there is a problem causing the low current on the controller., I use only 92 octane and change fuel filtere ever 10-15k. My first Q 's pump didn't quit but surely lost alot of its pump volume. I changed it out at 210k and it still had the oem controller in it when it was destroyed in fire at 240k,

[Q45tech]

You have to look at the running pump current with a ampere probe and an oscilloscope. The resistance measurement is just reading continuity of 1 set of [out of 8] commutaors and the associated coils.http://www.vetronix.com/pdf/ma...4.pdfh ... c49954.htm

I have seen a few failed transistors but the melted solder joint on the ground terminal outweighs them by 15:1!In all cases when a new controller is substituted the pump has failed in a shorted mode drawing excessive current due to running at half speed!

[aaacomp]

Didn't have the melted solder joint on connector. Inside the controller are what I beileve to be two voltage reg and maybe matching amplifiers ? So one of each on each side total 4 . with a srew type clamp both are held against the housing (heat sink). The short was on one of the amplifiers or voltage regs (Nec K591 part number BTY the Q's ECU has 4 of these inside it) The mylar was melted on the semiconductor and the path on the pcb charcoaled with path raised. The manual states a 5 ohm across the pump which is what I have now. To run the test you state I would have to install the new controller first. Since I don't have all the records on the car and the controller that I have to replace now has the telltale "Blue INk' on it I believe that this would be the third controller for the car.. In short there's a continued existing problem in the fuel management circuit. BTY thanks for the week end update advise..

[Q45tech]

I have examined over 45 controllers in the past 4 years and all but 3 worked perfectly once the pump was changed and the melted solder pad resoldered.........I have a stack of them but we don't resell them [use them in our 5 company cars] as it is not worth the warranty hassle nor the chance that previous abuse might make them failure prone.

Who wants to hear that a pump replacement failed again in a rainstorm 200 miles away.

I'm sure there is a failure mode where the transistors fail before the solder melts [say in winter] most fail in Summer.

You can just ground the pump and bypass the controller sure it will run wideopen and fail soon [Brand new maybe 6 months, used a few weeks].....we use alligator clips to crank the dead ones after the flat bed tow in!

Remember the pump relay supplies the +12 [to pump] and the controller the pump ground.

A 3 position 15 amp switch makes a great Burgler defeater/emergency bypass/normal operation device.

[aaacomp]

I think I'm going to put a toggle in the trunk for a anti theif device.. It would be pretty easy to mount it next to the relay,, Finished changing pump and controller.. Runs great again....Old pump still worked changed it to match a new controller for longevity.

[maxnix]

Great idea! Let us know and please post pictures of the project if you do it.

Did you test the old pump? Or just decide to do the obvious and expedient thing?

Your site seems to be down a lot lately, or is it me?

[aaacomp]

Tested the old pump via test in Shop manual (5 ohms) ... and got the right resistance. Tested in on the banch for operation.. still worked.. Didn't do the comprehensive test as described by Q45Tech ,, Removed the old pump via rear seat , sundeck removal. I've now done a pump R&R by both methods 1. Removal of rear seat 2. Removal of gas tank. If one runs as must gas as possible out the tank before removing I would say their both equal in time and degree of difficulty.I took down the INfiniti site since I was running two of them. I've had alot of people ask about it . I guess I'll have to get it back up and going.......

[tangalora]

Here's a closeup shot of the 1990 Infiniti Q45 fuel pump control unit underside ground pin which (in my case) overheated (due to a faulty fuel pump) and eventually created an open circuit.