My son got a '91 Ranger with a 2.3L EFI and a five speed. When he got it it wasn't roadworthy, it needed rear springs, grille, steering shaft, brakes, brake lines, front shocks, one day at pick n pull, a truck load of parts and a few days and it's roadworthy...
We have a problem...when we try to accelerate the truck will sputter and sometimes backfire. The engine runs fine to half throttle position then it acts like it's starving for fuel. If it's parked and you push the throttle about half way it will run to the rev limiter but if you push it all the way it'll sputter back down to around three thousand. It's also hard starting when cold, when it's warm it starts fine.
Checked the plugs (it has two sets ) they are fine, it runs like a dream at idle and if you rev it slowly.
Added fuel, replaced the fuel filter, checked timing, alternator isn't working (taking it in to get checked tomorrow) but the voltage is above 12v.
The fuel pump runs for five seconds and cuts out when you turn on the key, sounds OK, runs all the time when the engine's running. I haven't been able to check the fuel pressure yet (don't have gauge) but I opened the valve with a small screw driver while it was running, it doesn't seem to have allot of pressure and the engine sputters when I open the valve.

This is a fascinating engine! Like I said it has two sets of plugs and the ignition cuts out till the engine comes back to idle, seems to be ahead of it's time. I would think it should have more than a hundred hp . This truck has tall gears, it'll do a hundred km/hr in second gear easy and does about 1600rpm at 100km/hr in high gear, it's gonna need everthing that engine can produce to maintain the speed limit .

If anybody has any ideas I would really appreciate your feedback. Thanks.

 

Your description of what happens with your attempt to check fuel pressure makes the fuel pump a prime suspect as the source of the running problems. It needs to be checked.

Do you have any trouble codes? Many parts stores will check for them at no charge (AutoZone and similar stores). If you get any codes, post them here and we can be of more help.

 

I don't know if the check engine light works, never seen it. This is an OBD I system, the only locate parts store we have here doesn't read OBD I. My scanner doesn't either. I'm going to see if I can locate a gauge today.

 

Boy you guys have been busy on this one.

Be sure to flush the brake system with new Motorcraft PM-1 brake fluid.

Has the timing belt on this puppy ever been changed???? If not, or your unshure, you'll want to check it's condition.
If you have to replace it too, also consider changing the water pump while your in there.

I believe this year/model has two fuel pumps, a low pressure feed in the tank & a high pressure one on the body rail under the cab, drivers side, so before replacing anything, do a fuel pressure check. Some autoparts stores have a fuel pressure gauge in their "Loan-A-Tool" program, for a refundable deposit, so call around & see whats available in your area.
If you have a Harbor Freight in your area, they have one for about $20 in round numbers.
If you get it, you'll likely need some plumbers PTFE ribbon dope on the hose & gauge threads to make them leak tight & safe to use.
KOEO fuel pressure should be 35-45 psi. KOER at idle, with fuel pressure regulator vacuum hose attached, 25-35 psi. With the FPR vacuum hose disconnected, 35-45 psi.

If the fuel pressure is suspect, check the FPR vacuum line for fuel. If it's wet inside, the FPR diaphragm is leaking, so replace the FPR.

If the alternator isn't working, you may be pleasantly surprised by how much better it runs after the alternator is replaced, so don't throw any parts at it until the alternator output problem is put right.

I like michigan66's idea on pulling & posting any trouble code Numbers.

More thoughts for consideration, let us know how it goes.

 

You can use an analog VOM to check for the codes. A digital won't work so well, as you look for 'sweeps' of the VOM needle. I suppose you could try the digital and watch for voltage spikes depending on response time. I think the procedure is posted on the site.
There is a code reader available that blinks a led and beeps for each output, and you count beeps/blinks and watch for pauses between the outputs to separate the digits. Someone has them on closeout and I think there is a post within the last 4-6 weeks to that effect. It is more convenient than the VOM, but the results are the same.
The symptoms point to a lack of fuel. From the description of all that was necessary to get road-worthy, it doesn't sound as if the truck was maintained as well as one might want, so before condemning the pump, I would inspect and/or replace the fuel filter. I think you can remove it, and try to flow air through it to see if its blocked if you don't want to replace it. Hate to admit it, but I still have the factory filter on my truck. I haven't been able to find a replacement, but haven't looked real hard since it runs so well.
tom

 

Yup tomw is right, this an OBD-1 system, so some autoparts stores may not have a code reader or scantool that'll hook up to it for them to pull codes. Most in my area do use scantools that will, so call around to see whats available in your area.

tomw remembers right, there is a 'how too" for pulling OBD-1 codes yourself, in the "Tech Info" thread atop this forum.
With a jumper lead in the right place, you can use the vehicles Dash mounted CEL, a 12volt test lamp, or an analog multimeter on the 20 volt DC scale, to count the pulses or blinks, to extract any trouble codes.

Tom, he posted that he has changed the fuel filter.

I suppose the in tank fuel pump pre-filter sock could be clogged up & limiting fuel flow at higher rpm's, if the fuel pumps & pressure regulator check out.

 

I agree with all the thoughts. first thing to do in DXing is to read all codes, even pending codes I would fix/replace the alternator first. if you still have the problem. I would suspect a fuel pressure issue. you need to do a full series of fuel pressure tests. also when you removed the plugs to check them I hope you replaced at least the drivers side with new autolites or motorcraft. you can buy 4 of them for that side at wally world or rockauto for $14.

 

Oops. My younger sister bought a Pinto that would stall out intermittently. Finally figured out that it was running out of fuel when she tried to climb the hill to go through the Caldecott Tunnel. I drove back home, bought a 5 gallon gas tank, and proceeded to drain her tank, remove it, and remove the sock. I threw it away, and put it back together. I also added an underhood filter to protect the pump and carburetor.
The symptom there was slow loss of power and inability to run when a longish fuel demand was put on the system. She sure got a bargain because when she bought it the vacuum modulator hose was off the transmission, and the owner was positive it needed a new engine and transmission, as it idled poorly, and wouldn't shift. The things we do as kids...
tom

 

Had the alternator tested, works fine, discovered these units have two plugs, the bottom one was not plugged in, located the stray plug, plugged it in, works fine. This seems to have solved the fuel problem also. I can't find a fuel pressure gauge in this area for under two hundred bucks and nobody seems to own or loan them out here either so I rigged up a tire chuck and a 60psi gauge and that seems to work. I get a reading of 2 to 5 psi when we turn the key on and the pump runs for it's five seconds, at idle it maintains about 20psi and if you rev it it seems to maintain about 18psi. Does this sound reasonable? The engine is running great but it seems a little slow to fire when starting warm but haven't tried it cold since. As far as I can tell this truck has only one fuel pump in the tank, the fuel filter is along the left frame rail and as far as I can tell the fuel line goes straight to the fuel rail.

 

if your tester is accurate I think your fuel pressure is to low

 

Curios about your comments on the spark plugs powersmoked, why run two different sets?
I'm thinking of monitoring the fuel pump and maybe replacing it anyway, the fuel gauge stays on full, haven't had time to check that out yet either. The fuel pump and fuel gauge sender are together on the same unit aren't they?

 

Sorry, just can't help myself but in the case of one of my sons the fact that the truck will only accelerate to half throttle could be a good thing.....

Russ

 

You said you checked the "sparkplugs" I was commenting that if you checked them all, 3 of the 8 are tough to change so if you removed them I hope you swapped new motorcraft or Autolite plugs. I don't feel like reading this whole thread again but I am suspecting fuel issues. Have you done the starter fluid test

 

You have a point there RangerRuss..., but at a hundred horsepower this aint no speed demon .

 

Na I just checked and cleaned up the right four so far, it's running like a dream right now, the plan is to run it for a few weeks to see if it has any more bugs or burns oil or anything than change plugs, timing belt etc.