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Engine Stalls When Cold After Revving


nobbyv

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Hey guys, hoping someone can help: '97 Ranger 2.3L that I bought a few months ago as a Home Depot/dump-run truck.

The issue that I'm having is that before the engine has a chance to warm up, it will stall out after I rev it. So it starts fine, and will happily idle forever. But as soon as I give it some gas, it revs up but then falls down too far and stalls (I can "catch" it with the throttle, but as soon as I let off the gas it stalls). It's then very hard to restart immediately. After the engine has been warming for 5-10 minutes, all is good.

I've replaced: IAC valve (my first guess), all 8 plugs, wires, air filter, fuel filter and O2 sensors. I pulled the MAF, and it looks SQUEAKY clean (as in the previous owner must have replaced it within the last 5k or so), so I ruled that out.

Checked fuel pressure, seems OK. I got a nice 12-14" stream of fuel when I pressed on the Shraeder valve with the key in the "ON" position.

I also spent a good twenty minutes with a can of carb cleaner looking for vacuum leaks, and couldn't find any.

Anyone have any other thoughts on what to check?
 


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tomw

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The description leads me to think you have a fuel flow problem. I'd put a gauge on the fuel rail and check pressure with the vacuum line attached to the regulator diaphragm and with the line removed. When you step on the gas, the vacuum drops and should bump injector pressure a bit to help with the stumble from air going faster than liquid fuel when you open the throttle. The fuel 'rate' has to catch up to air, so a bump in pressure helps.
tom
 

WarHawk-AVG

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Mark_88

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Sounds like the Idle Air Control needs cleaning or replacement. Tried to find the youtube for this engine but couldn't see one that was specific...I know they are out there.

I you know where the IAC is and can get at it...check that...there is a test I believe for that like removing the vacuum line and if it doesn't stall then the module is toast...but my mind is fuzzy right now...
 

nobbyv

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Nope, no codes related to this.

Sounds like the Idle Air Control needs cleaning or replacement.
See my description. Just replaced the IAC valve.

The description leads me to think you have a fuel flow problem. I'd put a gauge on the fuel rail and check pressure with the vacuum line attached to the regulator diaphragm and with the line removed. When you step on the gas, the vacuum drops and should bump injector pressure a bit to help with the stumble from air going faster than liquid fuel when you open the throttle. The fuel 'rate' has to catch up to air, so a bump in pressure helps.
tom
I will try to do a more thorough fuel flow analysis (though as I mentioned, doing the quick-and-dirty check fuel pressure seems good).
 

tomw

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A closed system can develop pressure with just a small change in the volume contained. Liquids don't compress, so you can have pressure, and still lack volume.
If you depress the schraeder valve pin, and allow a 1/2 tsp of fuel to escape, you still have a cup or so in the line going back to the tank & pump, etc, but no pressure. The pressure drops by removal of a very small volume.
If the filter or sock were clogged, you could develop pressure, but not have flow enough to run over idle speed.(could)
tom
 

nobbyv

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A closed system can develop pressure with just a small change in the volume contained. Liquids don't compress, so you can have pressure, and still lack volume.
If you depress the schraeder valve pin, and allow a 1/2 tsp of fuel to escape, you still have a cup or so in the line going back to the tank & pump, etc, but no pressure. The pressure drops by removal of a very small volume.
If the filter or sock were clogged, you could develop pressure, but not have flow enough to run over idle speed.(could)
tom
Tom,
Good points. The fuel filter is new, but I guess the pump itself could be failing or there could be some other obstruction. It's just strange that it only happens for that first 5-10 minutes when cold.

I'll get a proper gauge on it.
 

Mark_88

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Sorry...didn't see that...but, then again...a replacement part is not always a working part...I can't remember if there is a test for that...like unplug the vacuum line and if the engine dies then it is working properly...if it doesn't affect it then the part is still not working.
 

tomw

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If the ECT or ACTS were bad, then the computer would not know Engine Coolant Temperature, or Air Charge Temperature.
The names may have changed from those mentioned, but the compter needs to know the temp of the air coming in and the coolant to be able to enrich the mix when cold... to avoid stalling when you step on the gas(YOUR symptom, I think).
The will have a specific resistance at a specific temperature, I believe. There's a table in the shop manual somewhere... They cost not a lot.
There also may be a thermal vacuum valve in the air box that operates a flap that allows warmed air from the sheet metal around the exhaust manfold to mix with cold air from the inlet on the radiator support, or only warm or only cold... into the intake. If it has failed, then you'll get cold, un-heated air that is harder to mix with fuel, but will be less noticed when the engine is up to temp. On a cold day, the vacuum should go to the diaphragm that diverts air so it comes from around the 'stove'. Warmed, that flap / diaphram will move to allow cold, un-heated air in.
tom
 

Daveo286

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Has anyone figured this out? I have the same exact issues.
 

Eam0885

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Has anyone figured this out? I have the same exact issues.
Curious as to if you had figured anything out regarding this issue as I am haveing exact same issue with my 97 2.3l as well and am at a loss.
 

Daveo286

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Curious as to if you had figured anything out regarding this issue as I am haveing exact same issue with my 97 2.3l as well and am at a loss.
I sold that ranger to the scrap yard.. but my only conclusion was that the intake valve was possibly stuck open or valve spring was broke letting fuel dump into the cylinder after the rev.
I replaced every sensor that had anything to do with fuel, air, or emissions and still no luck. I ended up finding a nicer ranger for $500 so I didn’t invest anymore time into the old one.
 


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