1991 Ranger cold starting problem!! - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 02-20-2014
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1991 Ranger cold starting problem!!

I have a 91 ranger 4.0 4x4. It has a starting problem. It used to start very quick as the starter turned over the engine. Now after sitting all night I have to turn over the starter quite a long time before the engine starts. What seems to work is if I turn it over for 3 seconds or so, stop, then turn it over again then it starts quickly on the second try. This happens overnight or whenever it has been sitting for a while. If I try to start it right after I turn it off it starts right up like it used to. When it has been a cold night in single digits it will start quickly in the morning just like it used to on the first try. Once started it acts like it always has with a higher rpm till it warms up. I am thinking it has something to do with how it gets fuel during the cold start and wondering how the system works during that time. Also wondering if the oxygen sensor is involved with cold start.
Just before the starting problem happened some things were done to the truck.
New clutch and an engine light that lead me to change the oxygen sensor and that fixed the engine light problem. Wondering if the oxygen sensor could be bad and if that could cause the starting problem?
Any help would be greatly appreciated as I need to go on a road trip soon.
I borrowed a fuel pressure tester and this is what I found.
With the key on and motor not running I grounded the fuel pump at the test plug and the pump ran steady at 40 psi.
When I stopped the pump the pressure dropped slowly, within 3-4 seconds to about 8psi and held there for the 30 minutes I checked.

From what I have read pressure should hold for at least 3 minutes after pump is shut off. I don't see any visible leaks and no gas drips from the vacuum line after I take it off the the pressure regulator.

When I run the engine the pressure stays at about 33 psi at idle and when I increase rpm it fluctuates up and down a little.
While it is running I removed the vacuum hose from the pressure regulator and the psi increased to 40 psi and held.

I am assuming the cold hard starting is because there is not enough pressure in the fuel lines by morning. Wondering if it could be the pressure regulator? or what?
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Old 02-20-2014
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Yes, fuel pressure is leaking out when engine isn't running.

For now, turn key on, count to 3, then turn key off, repeat two times, then crank engine.

The computer only turns on the fuel pump for 2 seconds when key is first turned on, it won't turn on again until RPMs are above 500, so cranking won't get fuel pump on.
So key on and off a few times will get pressure back up for starting.

As to the problem, with no smell of gas, the leak could be at the FPR(fuel pressure regulator) or the check valve in the gas tank(on the fuel pump)
The FPR is on the fuel rail it has a vacuum line attached, remove this vacuum line and check it for gas smell, if you smell gas replace FPR, that's your leak.
FPR could still be leaking fuel to return line.

If you have any rubber fuel lines near the gas tank you may be able to clamp the return line and then the fuel pump line to see if pressure holds, you would need the pressure tester again.
This would tell you if FPR or Fuel pump valve is the issue.

Also after shutting off engine warm, pull off the intake air plenum(tube) and open throttle plate, smell for gas smell, with fuel injectors there should be no gas smell.
But a leaking injector will cause a gas smell and a pressure drop.
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Old 02-21-2014
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thanks for the reply Ron. I unscrewed the return line from the pressure regulator and capped off the return port. I pulled the vacuum hose and no signs of smell of gas.
I jumped the pump again and while jumping it stayed at 40 psi but when I stopped jumping the pressure once again dropped as before. I did it again and this time capped off the vacuum tube and still the same thing. So does this mean the pressure reg isn't leaking and now it is either the check valve in the feed in the tank or the fuel injectors. If so is there a way to take a pressure test between the tank and fuel rail. Thinking at the fuel filter or I see in the engine compartment on the drivers side the braided fuel pump feed line has a ford line coulpler on it. How would I rig a pressure tester to these places.
also, the feed large fill tank hose has a leak in the upper part where you fill with gas so the tank is never pressurized would this have any affect on the loosing pressure at the fuel rail.
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Old 02-22-2014
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No, on the gas tank being air tight, that won't effect fuel pressure, but can cause EVAP system issue, but that won't effect performance.

Yes, looks like FPR is OK.
Did you see if you could smell gas in the intake?

There is another quick test you can do.
Start engine then shut it off.
Turn key on and off a few times, to build up pressure in the rail.
With key on/engine off
Push gas pedal to the floor and hold it there
Crank engine over, it should NOT fire, just crank, stop cranking.

The computer has a routine to clear a flooded engine.
Key on/engine off, gas pedal to floor sets this routine, this sends 5volts from TPS(throttle position sensor) to computer, and this tells computer to turn off fuel injectors.
So if engine fires with injectors off, then fuel in the intake must have come from leaking injector(s).

Yes, if you could find a way to put a pressure gauge on fuel line from pump then it could ID a faulty check valve on fuel pump.
I have never tried that so don't have a method to do it???
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Old 02-23-2014
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So.....all of a sudden the ranger is starting right away like it used to, just a few cranks and starts right up, even in the morning?? The only thing different is I added some antifreeze which was low when I opened the rad cap, but still had a high level in the overflow. Maybe I need a new rad cap. But the pressure gauge still shows the same as before, not holding pressure.
I did what you suggested Ron. First I let the truck run, turned it off, and then started it again and started right up. Then I turned the key on, put the pedal to the floor and turned it over for a long time but wouldn't start. Turned key of. Then started engine and started right away. Now I turned just the key on 8 times to build up the pressure. Kept the pedal to the floor and turned it over and it started right away. I did this three times just to make sure. So Ron according to what you said the injectors must be leaking when I turn the key on and that is why it started. Sounds reasonable. But...... I tried something a little different. I turned the key on and this time used a jumper at the test block to ground the fuel pump and make it run. I did this 8 times building the pressure to 40 and shutting it off and watching ther pressure drop immediately. Shut the key off then turned key on again. Put the pedal to the floor and cranked the engine for a long time and it would not start. I tried this three times and still it would not start. So I am confused.
Is there something happening differently when I am just using the key on to build up pressure that activates the fuel injectors and when I just build up the pressure jumping the pump that doesn't activate the injectors. Is there something wrong electrically here or is this normal??
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Old 02-23-2014
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The fuel injectors have no connection to fuel pump activity.
Computer starts injectors and spark after 1.5 seconds of cranking(1.5 seconds after seeing pulse signal from CKP(crank position) sensor).
"They" say the delay is to let oil pump push oil into filter but.....1.5 seconds???
Just bad code writing IMO, lol.

If engine is starting now, then you may have to wait to diagnose the problem.
Not sure why you would get varying results on the "flooded engine" routine, although if it started and ran then "flooded engine" routine was not initiated that time, if there was a leaking injector it would fire then die then fire and die a couple of times, when the cylinder with the leaking injector got spark, but it would not run since the other 5 cylinders would have no fuel.

Last edited by RonD; 02-23-2014 at 07:32 PM.
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Old 02-23-2014
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Quote:
Originally Posted by RonD View Post
The fuel injectors have no connection to fuel pump activity.
Computer starts injectors and spark after 1.5 seconds of cranking(1.5 seconds after seeing pulse signal from CKP(crank position) sensor).
"They" say the delay is to let oil pump push oil into filter but.....1.5 seconds???
Just bad code writing IMO, lol.

If engine is starting now, then you may have to wait to diagnose the problem.
Not sure why you would get varying results on the "flooded engine" routine, although if it started and ran then "flooded engine" routine was not initiated that time, if there was a leaking injector it would fire then die then fire and die a couple of times, when the cylinder with the leaking injector got spark, but it would not run since the other 5 cylinders would have no fuel.
The starting is no problem right now but the system is still not holding pressure.
Ron, maybe you can answer this: Why when I prime the fuel line using a jumper and use the "flooded engine" routine it Does not fire?
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Old 02-23-2014
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I do not know, if it was a leaky injector then it should fire and die, fire and die, ect....
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