Idling fine but stalls under load

mazdamama · Dec 20, 2014

My truck idles fine but shortly after putting it in gear it will die like the fuel cuts out, but if I give it gas very slow and smooth sometimes I can get it up to speed, but If I step on the pedal hard while the truck is in gear it just dies. This problem is worse when I turn the wheel also, but that might have something to do with the load placed on the engine by trying to turn 37s with an old stock power steering pump. I can rev up the engine when it's in neutral just fine.
It is a standard transmission..... And I do not attribute this to a transmission issue
It has codes for EGR circuit voltage and Mass air flow sensor voltage, as well as 02 detecting lean conditions but I attribute that to exhaust leaks

I have topped off all fluids and
Replaced MAF sensor, Crankshaft position sensor, Fuel pump

I am starting to suspect that it has something to do with the distributor
Or maybe a clogged catalytic converter.
I will check those soon but would greatly appreciate any advice before I throw anymore parts at it.

RonD · Dec 20, 2014

Your symptoms all point to lean condition, when you add more air engine stalls out.

After replacing MAF do you still have the MAF code?

MAF(mass air flow) data tells the computer how much fuel to add to the available air.
It is the big kahuna sensor for air/fuel mix.

TPS(throttle position sensor) tells computer when to add slightly more fuel to the MAF data mix, like the accelerator pump on carb.
It can and should be tested with a volt or ohm meter.

A simple vacuum leak would also explain the issue, a vacuum gauge is a good tool to have, $25.
You can also check for clogged exhaust with it.
Gas engine vacuum should be above 17" at idle.

Also after engine is warmed up unplug IAC Valve, it will close and idle should drop down to around 500rpms, or engine may even stall, either is fine it means no large vacuum leak.
If idle stays high then you do have a leak.

mazdamama · Dec 20, 2014

Thanks for the advice, I will check all of that stuff soon, the MAF could still have something to do with it.
Just to clarify, I can step on the pedal and rev it up fine in neutral, but if I turn the wheel or put it in gear and step on the gas it stalls

mazdamama · Dec 21, 2014

I think I figured it out.......Custom rock crawler issues...
So I have a ranger fuel pump in a bronco 2 tank, and very flexy suspension and a new few pump that doesn't read fuel levels the same as the old one, so apparently when it reads 1/8 tank it's pretty much empty and when the suspension shifts the fuel cuts out. Now for the other codes, I will have to do a little more work. But at least it runs.

RonD · Dec 21, 2014

"when the suspension shifts the fuel cuts out"
Could be a grounding issue.

Run a few ground straps
battery ground should run to starter motor bolt or block
Ground strap needed from:
head to firewall(computer ground and instruments)
Block to Frame(lights and fuel pump)
Rad support to battery negative(head lights)

You should probably bend that float arm up a bit, must be hitting the bottom of the tank too soon.

Idling fine but stalls under load

mazdamama

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mazdamama

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mazdamama

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