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Mazda Ed
Mazda Ed, Auto Service Technician
Category: Car
Satisfied Customers: 2223
Experience:  ASE Master Technician, Mazda Master Technician, GM and Ford factory trained. 15 years experience!
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92 Ford Ranger: Hard start, idles rough then smooths out..throttle

Customer Question

92 Ford Ranger. Hard start, idles rough then smooths out. Will not take any throttle until is smooths out. After it smooths out, only minimal throttle can be applied. If the throttle is wide open it will backfire/miss and if not released, the engine will die. If throttle is applied slowly, the trunk will move down the road smoothly. I replaced the MAF sensor, no change. The fuel pump runs constantly. When I turn the key on (no starting), it will not build up pressure and stop running. I was so sure it was the MAF. Any ideas?
Submitted: 7 years ago.
Category: Car
Expert:  Mazda Ed replied 7 years ago.
Hi, have you tried checking the actual fuel pressure? Also, you can try checking the pressure (deadheading) right after the fuel filter. If it builds pressure and holds, then you have a leak further up in the system. Perhaps an injector is stuck open or the pressure regulator is leaking.
Mazda Ed, Auto Service Technician
Category: Car
Satisfied Customers: 2223
Experience: ASE Master Technician, Mazda Master Technician, GM and Ford factory trained. 15 years experience!
Mazda Ed and 11 other Car Specialists are ready to help you
Customer: replied 7 years ago.
If I have a fuel leak, where would the fuel go...I don'e see or smell and leaks. When I turn the key on, the check engine light seems to blink/pulse in sync with the fuel pump and so does the led on my cheap code reader I have. Is it possible the fule pump has a clogged intake or simply is not putting out enough pressure for the regulator to switch it off? I've purchased a new fuel pump and screen. If I can figure out how to get all the crap disconnected from the top of the tank so it will drop to the ground, I'll replace the pump...what is the trick to disconnecting the fuel lines and wires when you can barely reach on top of the tank after removing the scraps? Do I have to remove the pickup bed to get access?
Expert:  Mazda Ed replied 7 years ago.

If the fuel is leaking, it is possible it is leaking from one of the injectors right into the intake and being burned as soon as the engine starts. Or if the fuel pressure regulator is faulty it could be going out the return line and being sent back to the tank.

I find it's usually easier to remove the bed to access te fuel tank and lines. At this age, everything near the tank is probably rusted and brittle. I wouldn't be so sure that there is a problem with the fuel pump just yet. Also, if the code reader is removed does the pump still run continuously? Does the CEL stil blink with the code reader removed?

Another step you can try is to disconnect the MAF sensor... start and run the vehicle like that. If the symptoms are gone, it's possible that the replacement MAF sensor is faulty or more likely the engine is sucking air someplace between the MAF sensor and the intake. Spray carb cleaner on the rubber intake air hose and all around the base of the intake manifold. If your idle increases then you have a vac. leak that needs to be repaired.

Customer: replied 7 years ago.
Reply to Mazda Ed's Post: You were right, the fuel pump didn't fix the problem. OH! what a difference removing the bed to work on the fuel tank instead of laying underneath on the ground.

The CEL blinks very rapidly with the key on and the fuel pump running. The pump runs continuously with or without the code reader attached. I have unplugged the MAF and there is no difference.

Wouldn't a vacuum leak be less noticable at higher RPMs? I can't get the the engine to rev up without it coughing and spitting and backfiring through the the intake I believe.

What do you want me to do next. If I need to test fuel pressure, I've to purchase a fuel pressure tester.
Expert:  Mazda Ed replied 7 years ago.

Hi again, I'd really like results from a fuel pressure test. Does the CEL only blink with the vehicle running? or with the engine off but the key in run??

Unplugging the MAF puts it in a sort of fail safe mode, so we should be able to rule out air delivery for now. It really sounds like a fuel problem. Enough gas to let it idle, but under load it bogs because it is running lean.

You should be able to rent a fuel pressure gauge from one of your local auto parts stores if you don't want to purchase one. Also, if you still have the tank accesible try removing the return line and checking how much fuel comes out of it with the pump running. It should have NO fuel until it overcomes the regulator pressure. If it just comes pouring out as soon as you turn the key on, then it sounds like the regulator has failed. It is cheap from Advance Auto.. less than $20.00 and looks like this:

Click to view enlarged image

Let me know what you find with the fuel pressure testing.

Customer: replied 7 years ago.
THE CEL only blinks rapidly when the key is on but the engine is off. When I do get the engine to start (very hard to start almost run the battery down before it will idle) The CEL stays on, but not blinking.

I had that pump in my hand but don't remember. Is the small tube the return? I have the bed laying in the front yard. It won't go back on until the truck runs right.

I don't know why I'm fixing this thing. Guess I can't afford to buy something better. The front neoprene oil pan gasket squisked out and the trunk was going through 3 quarts of oil a week for the past 6 months. While the trunk has not been running, I have managed to get the gasket pushed back in place without dropping the pan. I'm going to take a punch and knock a couple of dimples into the pan flange so the gasket won't come out again.
Expert:  Mazda Ed replied 7 years ago.
The return line is the line not connected to the fuel filter. I know the feeling of trying to keep an olddie running. I have a 1989 Ford Probe with 170k and a 1994 Mazda B3000 with 120k and those are the nicest ones of my fleet ;) It is probably extremely hard to start because it won't build fuel pressure.
Customer: replied 7 years ago.
Reply to Mazda Ed's Post: I couldn't find a fuel filter so I just replaced the regulator. I has to take the upper intake mainfold off and the fuel rails off to get the screws. When I put it back together, I didn't get two of the injectors seated perperly and they leaked when I turned on the key. I tore down again and this time I did not put the upper mainifold back on before testing the injector seal in the fuel rails. When I turned on the key I could hear fuel spraying into one of the cylinders and I could look into the intake and see the pool of gas in the intake for that cylinder. I removed the injector. Is it possible that an injector stuck open could have caused all this? Can the injector be fixed?
Expert:  Mazda Ed replied 7 years ago.
It's is quite possible the stuck open injector caused this... if you look back to the beginning of our conversation that was one of the first things I mentioned. By checking the fuel pressure and watching the return line we were quickly heading in that direction. You will just need to replace the injector. A new one is about $45.00 from Advance Auto.
Customer: replied 7 years ago.
Reply to Mazda Ed's Post: the injector did not fix the problem. The fuel pump does not stop running. I have removed the upper manifold and turned the key on to make sure that fuel is not leaking into the lower intake. I used a piece of folded paper and inserted it into each port to see if it came out dry and it did. I removed the return line and fuel is coming back to tank as fast as it leaves the tank. Is it possible that this system works that way, not building up pressure to cause the pump to stop, but rather the regulator creates resistance so pressure will build in the fuel rails for the injectors but the fuel is always flowing back to the tank. Anyway, the problem still exists.
Expert:  Mazda Ed replied 7 years ago.

The regulator is there to regulate the pressure. By removing the return line, we were trying to check if it was doing its job. It is supposed to maintain the pressure in the rails at a certain spec... when that spec is exceeded then the regulator opens and fuel returns to the tank.

Fixing the leaky injector is definitely a start! It appears that you had/have multiple problems. Were you able to locate a fuel pressure gauge so we can take some readings? I'm going to get my reference material for this truck... be back in a few minutes.

Expert:  Mazda Ed replied 7 years ago.

Ok, lets try something relating to the fuel pump not shutting off....

Look in your Power Distribution Box under the hood. I believe it is on the driver side near the battery. There should be a relay labeled fuel pump in there. Remove this relay and make sure the pump does not come on with the key in any position.

Assuming the pump shuts off, try swapping the fuel pump relay with another relay and see if it now works correctly. It is possible the fuel pump relay is stuck on due to corrosion.

Let get the fuel pump constant running figured out first!

Customer: replied 7 years ago.
There is only one relady and it is for the fuel pump. When I pull it the pump stops. Since I didn't have another relay, I put 12vdc across the coil leads of the relay and I can hear and feel it clicking.
Expert:  Mazda Ed replied 7 years ago.

2 more items for you to do:

#1)Since you replaced the injector, you should disconnect the battery for 30 minutes to force the computer to relearn the fuel trims. It was detecting an overly rich condition from it dumping fuel in the intake and leaned out the long term fuel. Now that you fixed that, it is probably still stuck on full lean.

#2) Disconnect PCM and remove fuel pump relay. Then check continuity from the data link connector under the hood to a good ground. With both components disconnected there should be no continuity to ground. It should be a completely open circuit. I believe it is a Light Blue wire with an Orange tracer. While holding the DLC in your hand and looking at the terminal side it should be the one in the lower right corner. There should be an empty cavity next to it.

If you have continuity then you have short to ground in the wiring harness betwen the Relay and PCM. This will keep the fuel pump running all of the time. If the wire measures ok, then we will need to check inputs to the PCM.

Customer: replied 7 years ago.
Reply to Mazda Ed's Post: PCM is the same as ECM/ECU/computer right?

I got NO continuity with the pcm and fuel pump relay disconnected. Just to make sure I had good ground contact with my multimeter, I connected the fuel relay and did get a reading, remove it and get no reading.

What's next chief?
Customer: replied 7 years ago.
Relist: I still need help.
Expert:  Mazda Ed replied 7 years ago.

I'm not sure why this dropped off my question list!

At this point, either the PCM is faulty or its getting a reading that tells it the vehicle is running and that is why the fuel pump continues to run as long as the key is on.

Since it is accompanied by the rapid blinking of the CEL I think you have an internal fault in the PCM.

Customer: replied 7 years ago.
Reply to Mazda Ed's Post: We come to that conclusion last because it is the most expensive to replace?
Expert:  Mazda Ed replied 7 years ago.

No, because that is where diagnostics lead us?? The PCM is commanding the fuel pump on all the time. We know this because there is no short to ground on the relay control and no short to power on the fuel pump feed.

I wanted to rule out all the things that could be easily checked first.

If you have an Auto trans here are some computers you could purchase:

1992
Engine Computer
Ford Ranger
Ele Cont Unit (ECU), (3.0L), AT- 162000AI006$25Davis Auto Center, Inc. USA-VA(New-Church) Request_Quote 1-800-446-8544 Request_Insurance_Quote268
1992
Engine Computer
Ford Ranger
3.0L AT 980869$25Shelby and Sons, Inc. USA-IL(West-Frankfort) E-mail 1-800-241-7278556
1992
Engine Computer
Ford Ranger
3.0L AT AC F27F-12A650-LB 991051$25Shelby and Sons, Inc.USA-IL(West-Frankfort) E-mail 1-800-241-7278556

 

If you have the manual trans:

1992
Engine Computer
Ford Ranger
AR107P$35Benny's Auto Parts USA-KY(Mount-Sterling) E-mail 1-800-992-3475310
1992
Engine Computer
Ford Ranger
Ele Cont Unit (ECU), (3.0L), MT-F27F-AA 5-2775$35Alexis Auto Parts USA-OH(Sylvania) Request_Quote 1-800-336-9197 Request_Insurance_Quote
249
1992
Engine Computer
Ford Ranger
F27FAA,#jjg6 #jjg6$35Hy-Way Service, LLC USA-ME(Milford) E-mail1-877-884-4568 / 1-207-827-5568614
1992
Engine Computer
Ford Ranger
TESTED AF4-38$2568 Salvage, Inc. USA-TN(Sweetwater) E-mail 1-888-820-7654450
1992
Engine Computer
Ford Ranger
TESTED OK 3.0 5-SPD. GUARANTEEDA040728$17.95Marshalls Auto Parts, Inc. USA-OH(Circleville) Request_Quote 1-800-333-2104 Request_Insurance_Quote
211

 

At those prices I would say that is the cheapest thing you could replace! Please remember they only part I recommend replacing was the regulator if you couldn't take a fuel pressure reading and that was because you said you could not see or smell a leak. I've tried to lead you on the best path possible to solve this problem.

Customer: replied 7 years ago.
Reply to Mazda Ed's Post: I'm not complaining, In fact I'm grateful to have someone to talk to about the problem. I'm also wondering if the PCM is controlling the spark advance and that's why it's backfiring when I get the RPMs up and stomp on the gas pedal.
Make no mistake about it, I've looked forward to getting your emails and trying the next thing that might fix the problem.

Kenny
Expert:  Mazda Ed replied 7 years ago.
Sorry, I took that as a complaint. It's quite possible there are other issue going on inside that PCM. At this point, I can only guess about the internals. I have no way to diagnose besides checking inputs and outputs. I would get one of those PCMs with the assumption that it will fix the constant fuel pump on problem..... and hopefully be what is causing the other problems too!
Expert:  Mazda Ed replied 7 years ago.
I assume you are locating a PCM since I haven't heard from you. I just wanted to let you know that I will be without internet access from 8/11 to 8/20 so I won't be able to respond. As soon as I get back I will check to see if you made any progress.
Customer: replied 7 years ago.
Reply to Mazda Ed's Post: I got the PCM and installed it. It changed things, but nothing good. I can now only keep the engine running with the pedal on the floor. The fuel pump stops now after a few seconds, so that's one thing. When I do get it started, it runs rougher and will not idle. The old PCM would not support pedal to the floor, but it would idle. I'm at a loss. If I didn't know better, I'd think the valve timing slipped. Hope you have an idea.

Kenny
Expert:  Mazda Ed replied 7 years ago.

Has the CEL rapid blinking also stopped?

When the pedal is pushed all the way to the floor to get it started does the engine race after that or does it just try to idle?

Also, with the amount of unburnt fuel that has run through the exhasut.... it is quite possible there is an exhaust restriction. I just scanned through all of our posts and didn't see anything relating to the exhaust. You may want to remove the exhaust pipe before the convertor to see if you now have a large exhaust restriction. Or if you have access to a backpressure gauge remove the O2 sensor and take a reading.

Customer: replied 7 years ago.
Reply to Mazda Ed's Post: I'll get on this this weekend and advise.
Expert:  Mazda Ed replied 7 years ago.
Ok! Can't wait to find the final resolution of this problem. It's a challenge that keeps me on my edge!
Customer: replied 6 years ago.
Reply to Mazda Ed's Post: The code scanner works now. I can't seem to decypher it, but it works like the book describes it. The scan codes work out to something like "fix all these possible things then rescan to find out what wrong".
With the engine running, badly, pedal to the floor, RPMs around 2K, i have exhaust gas coming out the tail pipe as normal.
Expert:  Mazda Ed replied 6 years ago.
What code are you getting from the scanner?

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