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Diagnostic Help

  #1  
Old 4 Weeks Ago
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Icon4 Diagnostic Help

Hello all, I'm new to this forum but love it so far!

Anyways, my 97 Ranger is starting, but then stalling out almost immediately. I am able to rev it up as soon as it starts, and I can keep it going if I am pumping the gas, but as soon as I let up it dies.

First I changed the IAC thinking it could be that, but it made no difference. Then I checked the fuel pressure and noticed it was only 5psi. I think changed the fuel pump, but still no luck. Any idea where I should look next?

Thanks!
 
  #2  
Old 4 Weeks Ago
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Welcome to the forum

What engine do you have in the 1997 Ranger?

Is it a warm cold thing, or at this point just cold start issue since it doesn't stay running

Yes fuel pressure should be around 30psi, I assume you changed the fuel filter when you changed the pump

Whats the pressure now?

1997 and older Rangers used a Return fuel system, running 30-40psi pressure
In the gas tank is the fuel pump, fuel runs from pump to the filter and then from filter to the Fuel Rail on the engine
The fuel injectors are connected to the fuel rail
On the end of the fuel rail is the Fuel Pressure Regulator(FPR), it has the Return fuel line that runs back to the gas tank
FPR also has a Vacuum hose connected

The FPR has a spring inside that holds a valve closed, the spring is set to hold pressure up to 40psi, so above 40psi valve will be pushed open, and extra fuel will flow back to the gas tank
The vacuum hose pulls against the spring pressure, so when engine is running you get stable fuel pressure at the injectors, 25-35psi

There are only 3 ways to lose fuel pressure, besides a broken fuel line, lol
Fuel pump check valve
FPR valve
Open/leaking fuel injector

There is no "gas" pedal on a fuel injected engine, we still call it that but without a carburetor and accelerator pump at the other end of the gas pedal's cable no gas is pumped into the engine when you press down on the "gas" pedal
Its an "air" pedal now, pumping the pedal lets in more AIR
On the throttle plate there is a TPS(throttle position sensor), computer uses this for driver input, and will add more fuel, when engine is running!.......under 400RPMs it does "almost" nothing
If letting in MORE AIR keeps engine running then could be engine is flooding out, so too much fuel

All fuel injected engine computers have a "Clear Flooded Engine" routine built-in
Turn on the key
Press gas pedal down to the floor, and hold it down all the way(the almost part), when computer sees TPS at Wide Open Throttle(WOT), AND engine at 0RPMs it will enter "Clear Flooded Engine" routine
This means it shuts OFF fuel injectors but leaves Spark on, to Dry out a Flooded Engine

Now Crank engine over, it should NOT start, it should NOT fire at all, no fuel
If it does then you have a leaking injector or FPR(vacuum line sucks in fuel)
As soon as you release gas pedal injectors will start, even while cranking, I use this every morning on my high mile 4.0l engine, gets oil pumped thru engine before I let it start by releasing the pedal

IF engine fires
Check the Vacuum hose on the FPR for gasoline, remove it and see if gas is inside, if so replace FPR
To check injectors takes a bit more work, first disable spark, unplug connector on coil pack
Cycle key on, count to 3. then off, do that 3 times, builds up fuel pressure
Now do "Clear Flooded Engine" routine, and crank engine 5-10 seconds 2 or 3 times
Now remove spark plugs, you are looking for the WET one, that's the cylinder with leaking injector
 
  #3  
Old 3 Weeks Ago
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Hey Ron,

Thanks for all the help, I really appreciate the long response. I followed a lot of your advice and got down to it maybe being a leaky fuel injector. However, by that time it had been over three weeks and the girlfriend put her foot down lol. So this morning it was towed away to a shop...will keep you updated after I get the diagnosis.
 
  #4  
Old 3 Weeks Ago
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Back in my Gen 2 lightning days there were 2 problems:
1. fitting just above the fuel pump would crack and allow fuel to bleed
2. The high speed fuel pump resistor would go out. (not even sure if a ranger has such a thing?)
 
  #5  
Old 2 Weeks Ago
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Howdy all, so after giving up and taking the truck into the shop, the problem ended up being faulty spark plug coils. 1 was dead, and 2 were failing.

How would I go about trying to diagnose something like that in the future?
 
  #6  
Old 1 Week Ago
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Coil pack doesn't make sense from your description but if thats what it was, then thats what it was.
One coil inside the pack can start to fail, not common but can happen, so you get misfires, but the other 2(in a 3 coil pack) will continue to work just fine, so what you/they found is quite rare, the whole coil pack still needs to be changed when a single coil fails but the other two should test fine.

Yes, coils can be tested, since the early 1900's, and its pretty easy, you need an OHM meter

Video here: youtube.com/watch?v=c1zhgsnyZWw

Year doesn't matter, ignition coils all work the same way and will have the same OHM ranges for the most part
 
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