4.0L stalls during heavy load uphill...only hot days

[Klainmeister]

Hi all,

I've been a long time reader of this forum and after doing a series of repairs on my truck, I figure I could dish advice as well as receive.

The problem I have had has last for nearly a year now. When driving over mountain passes and flooring the throttle to kick it into 3rd, the engine will run fine for about 2-3 minutes then lose power, stall out, and the fuel pump in whining in the tank. What have I done?

Replaced the fuel pump 3 times in the last year
Replaced fuel filter twice
Replaced plugs about 10k ago and wires

The part I cannot figure for the life of me is why it only happens in the afternoon on toasty days. I thought it was fixed over the winter, but that was because it was cold as all get out. Since the pump was whining and when it stalled it seems that the engine isn't recieving fuel, I always figured it was the pump....but 3 pumps in under 10k? What the deuce?

Any advice would be greatly appreciated.

4.0L 1994 Mazda B400 4x4, 92,000

 

[Earl43P]

Next time it happens, see if you still have spark.

Ignition modules are known to fail from heat.


I'd also depress the schraeder valve on the fuel rail and see if fuel pressure is still present, just to rule that out for good.

 

[Klainmeister]

I did do a spark test by removing a plug and letting it discharge against the intake manifold. Seemed fine--plenty of spark.

I haven't done the schrader test....that's a good idea...although it really does seem like it's not getting fuel--as if the pump is overworked and stops pumping or something.

After about 30 minutes, it'll start up fine and as long as I'm not doing more climbing, usually can get me home.

 

[Colin]

have you checked the air filter? if its all clogged up the engine wont get enough air, especially on hot days/working hard

 

[Klainmeister]

Just checked the air filter--all is well--and checked to make sure the throttle opens fully under full pedal depression. Everything checks out. Where to look next?

 

[Colin]

have you checked fuel pressue yet like Earl mentioned earlier?

 

[Klainmeister]

No I have not...mainly because living in such a sparse, hot, and inhabitable environment, getting stranded on a hill mid-afternoon isn't ideal. That said, let's say that I do not have pressure at the rail, what would that indicate, or vice versa? That way I can know depending on what happens.

Thanks a ton guys, this is driving me nuts.

 

[Earl43P]

Might throw a fuel pump relay at it, since they are prone to failure and relatively cheap.

http://www.therangerstation.com/forums/showthread.php?t=86681 is an interesting read.

 

[Hellcat]

What RPM are you running when you pull the hill ? When it dies dose it just shut down all at once or dose it sputter like its running out of fuel ?

 

[Klainmeister]

Ok, I have replaced the relay...forgot to mention that. As for RPMS--usually it's being sustained neer 3k in 3rd heading up some of these passes at about 60-65mph.

It starts to lose power...like I cannot mash the accelerator anymore until it finally putters and dies. If I try to start it again, the starter and everything seems fine, just no fuel as far as I can tell. Maybe I need to spruce for a higher end fuel pump. These airtex and other pieces of whatever don't seem to be as strong as a good ol' bosch or something else.

 

[Hellcat]

Ok, I have replaced the relay...forgot to mention that. As for RPMS--usually it's being sustained neer 3k in 3rd heading up some of these passes at about 60-65mph.

It starts to lose power...like I cannot mash the accelerator anymore until it finally putters and dies. If I try to start it again, the starter and everything seems fine, just no fuel as far as I can tell. Maybe I need to spruce for a higher end fuel pump. These airtex and other pieces of whatever don't seem to be as strong as a good ol' bosch or something else.

Have you checked your throttle and kick down cables to see if your getting full extension on them ? I also pull some steep long hills and I was maxing out at about 3K RPM then the truck would shudder and act like it was running out of fuel. Adjusted the throttle and kick down cables now I can run over 4K RPM up the same hill and never have a problem. I never had the problem until summer hit. Your problem may be entirely different I am just sharing what I learned from mine.

 

[289-tiger-]

If you have fuel pressure, spark, timing and compression working to your advantage and it is still dying uphill... I hate to beat a dead horse on previous threads but take a look at the MAF. However those engineers in the early 90s worked this part into the system confuses me. It will mess with your fuel delivery cause knocking (have not had the vehicle stall completely though) and not show one single code during the process.

Good luck