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I am a little frustrated but the reason you get all these replys that are basicly the same is that my email server was messing up and I thought I wasn't sending the original message. Sorry. I also replaced the fuel pump last night very late. I wanted to make sure that it was not a fuel pressure problem. That's why I'm so frustrated. The fuel pump, fuel filter and pump relay are all new now and I'm getting spark but no fire. So dosen't that take us to the throttle body itself?
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I had family day yesterday so I didn't work on the truck. I ran it today until it died (20 min) and tried restarting it. It wouldn't. So I tested all of the plug wires to see if they were sparking. They were. Then, just for curiosity's sake I put a little more that a teaspoon of gas in the throttle body and tried cranking it. It tried to start. Why will it run for 20 min. and then something shut the injectors? Cause it wouldn't even try to start with the fuel pump jumpered. You're the diagnostic man, but I think that something is telling the injectors to shut and not cycle. What's your vedict?
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Patience is sometimes hard for me. Persistance? You convinced me. Talk to you tomorrow.
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Texas Panhandle. I will give that a shot first thing in the morning. But with the history, it'll probably start up and run for a while. I'll just have to drive it and get stuck. Maybe not to far from my house this time :>). Anyway I'll give it another shot in the morning and let you know.
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Sounds like this is going to take more than I can do. I'll just have to bite the bullit and take the truck to a mechanic. Wish you were close, since you already have a history with it, I'd bring it to you. Thanks for all your help!!!
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No hostility, just letting you know that I made sure it was plugged in right. It's just I'm usually good at troubleshooting problems with my vehicles but this one's got me confounded. I still haven't found the problem. After I emailed you last I took the truck out for a drive to see how it would go and it quit again. I took the jumper with me and followed the steps you gave me to hook it up. I heard the fuel pump running, but this time the motor wouldn't start. I turned off the key and disconnected the jumper and went through the steps again. Fuel pump ran the whole time I tried cranking. It tried starting a few times but wouldn't run this time. The friend that towed me home suggested that the pump may be running but not pumping. I don't know. I'm stumped. Do you have any more suggestions. I'm greatful for ALL your time and suggestions.
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I will change the oil, though it's not that old and does not smell gassy. There was only one plug of the type that would fit the sending unit, and it IS plugged in right. I am a little suspicious of the new unit as the oil pressure does not change that much while running through high and low rpm's. What I mean is that when I start the motor the oil pressure is 20lbs at idle and when I take it up to 2500 - 3000 rpm's it slwoly moves up to 30-35lbs. When I let off the gas it slowly comes back down to 25-30lbs at idle. I'm used to the gauge reacting a little faster and haveig consistant high's and lows. I don't remember if they asked me if I had a gauge or light, I bought it 10 days ago, but they are shaped the same and have the same three prong plug style. Should I replace it?
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Funny you should say something about the oil pressure switch. Where is that located? Is it integrated into the oil pressure sending unit? The reason I ask is that my sending unit went bad a few weeks ago (reading high). I just replaced it a few minutes ago and when I went to restart the motor it started and died. It did this a couple of times. Finally it ran consistantly through high and low RPM's. Is this the end or do I need to look for a seperate oil pressure switch? BY the way, the oil pressure on the new unit was reading 20lbs idling and 30lbs @ 2200 rpm's.
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OK, here's what I did, after I emailed you this morning (while I was waiting for your reply) I went ahead and got a new fuel pump relay and installed it. The truck is 12 yrs old and has 240k miles on it so I thought it couldn't hurt. the truck started fine and idled for 13 min. I decided to rev up the engine and as it was idling down it died and wouldn't restart. After I got your email I tried what you told me. With the new relay in I put a jumper from the gray wire on the relay to the + post on the battery. I could hear the fuel pump running I started the truck and let it idle for 5 min.. I decided to rev up the engine and it kept running. I let it warm up to running temp and did it again and it kept running. So I decided to disconnect the jumper and the truck kept running. I rev up the engine, it ran. I let it run a little while longer and then shut it off. It started right back up. I did this a few times and it kept restarting. The only thing I didn't do is drive it. I don't know what happened or why it's running now. I'll listen to any suggestion why. I'm going to let it cool down and see if it will keep performing well. I will let you know. thanks for your help so far as I'm not convinced that this problem is cured.
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I followed the harness from the fuel pump relay and the first female only connector was under the air filter on the lead to the coil. I traced from the relay every direction multiple times. The only lead that was taped to the harness by the relay had two ends plugged together.
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Answer to first question: I disconnected the return gas return line connectet a clean hose to it and ran it into a bucket. When the engine would start, the short time it was running it ran a full stream back into the bucket, but I did not pressure test it. Second: I had the transmission rebuilt about 13k miles ago (in march). before that was the fuel pump. I tried cycling the key 3 times and starting on the 4th, it idled for 10 min. and then died. Engine temp. was about 140 deg.
Thanks
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I have a 92 GMC 1/2 ton 2wd w/TBI that stalls when you let off the gas. And then it's hard to start again. I've replaced the fuel filter. Fuel pump is about 40K miles old and seems to be working fine. What's next? Thanks for the advise.
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You stated: "seems to be working fine".
Question: How did you determine this ?.
What was the LAST repair on the vehicle ?. ANY repair of any nature ?. In most cases problems that arise days, weeks or even months later can usually be traced back to the previous repair.
Try this TEST:
Cycle the ignition key from the OFF position to the ON position 3 times, Do NOT try and start the engine during this test.
On the fourth cycle try and start the vehicle and let me know.
autohelp
autohelp
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OK. Locate the fuel pump relay of which is usually mounted in the engine compartment. Look at the electrical harness jsut before the relay and you will see a female connector taped to the harness that is NOT connected t anything. This female connector is the FUEL PUMP TEST LEAD.
Using a standard 12 volt test light, probe this connector and turn ON the ignition switch and observe the test light, It should illuminate for 2 seconds and then go out.
If it does this, We can proceed.
Leaving the test light installed start the engine and observe the test light, It should stay illuminated all the time that the engine is running.
If it DOES, We can proceed.
Take a TEN (10) AMP FUSED jumper wire and attach one end to the battery POSITIVE terminal and the other end to this TEST CONNECTOR, Thus providing battery voltage to the TEST CONNECTOR at ALL TIMES as long as you have your TEN AMP FUSED jumper wire installed. You can hear the fuel pump running constantly.
Leve this TEN AMP FUSED jumper in place and start the vehicle and see if your problem is resolved.
let me know so we can proceed.
autohelp
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OK, Then locate the fuel pump relay and here is what you should have at these fuel pump wire locations at the relay:
Turn the ignition key to the "ON" position ONLY. DO NOT try and start the engine. OK, With the ignition in the "ON" position via the key:
Locate the GRAY wire at the fuel pump relay and using your 10 AMP FUSED jumper wire, Connect this GRAY wire to battery voltage and you should hear the fuel pump run constantly as long as you have battery power to the GRAY wire.
Now see if the vehicle will start and remain running.
let me know.
autohelp
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A bit SKEPTICAL is a GOOD thing.
OK, Here is how the fuel pump operates:
1. When you turn the ignition (key) past the ON position to the start position, There is a 2 second fuel pump run as soon as you turn the key to the ON position on it's way to the START position.
This 2 second pump run is provided by the fuel pump relay.
Once the engine starts, The fuel pump relay is no longer needed and battery voltage is supplied to the pump via the vehicles ECM (computer) and on SOME engines, Through the oil pressure switch, Then back to the fuel pump.
Let me know.
autohelp
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Are you POSITIVE that the oil has not been diluted with gasoline from this problem ?, As this can cause the oil pressure NOT to close thus shutting off battery voltage to the fuel pump.
There also is the possibility of a faulty NEW oil pressure switch.
Usually the factory wiring harness has 2 (TWO) connectors for the oil pressure switch.
One connector is for if you have an oil pressure LIGHT and the other is for an oil pressure GAGE. Make sure you have the right one plugged into the oil pressure switch.
When you bought the new pressure switch did they ask you if you had a LIGHT or a GAGE on the dash ?, As the pressure switches are DIFFERENT and NOT interchangeable.
I would change the oil and filter FIRST.
Second would be check that you have the correct connector plugged onto the pressure switch and that is is plugged onto the pressure switch CORRECTLY.
autohelp
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Do I sense some hostility per your statement: "and it IS plugged in right."?.
I would install a known good external oil pressure tester just to see EXACTLY what pressures your engine is doing, Before I return it and buy another one.
autohelp
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When it quits running and you are trying to get it started are you getting sufficient ignition to ALL the spark plugs ?.
What I am leading up to is a possible CRANKSHAFT SENSOR intermittent failure, IF applicable to your vehicle and type of engine.
autohelp
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Hang in there a little longer and just check the spark plug wires for ignition when you are trying to start the vehicle after it quits.
We almost have a diagnosis here.
I am in New mexico, Where are You ?>
authelp
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Haul that vehicle out here to Grants NM and I know I can diagnose and resolve your problem.
I have a 1 ton 1994 Ford dually and a flat bed trailer and on several occassions I have picked up vehicles and brought them back here and within a day or two, depending upon parts availability, The owner came and drove the vehicle back home.
I have even made house calls up to 150 miles from my home. But I am NOT cheap, But I do have 20+ certifications from GM, FORD, CHRYSLER and JAGUAR and also held several ASE certifications prior to retirement.
A couple of more tests won't kill you, Patience and persistance is the key.
autohelp
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I am teaching this trade to my son who has ZERO patience until I showed him what he would be making in a few years. I think he changed his attitude. You don't have to get dirty diagnosing electronic problems and it pays extremly well.
autohelp
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If I had access to the vehicle I would have your answer in 30 minutes or less, But doing it this way takes time and testing.
OK, If you are using the jumper wire CONSTANTLY attached to the fuel pump gray wire and you are getting the same results, It is time to install a fuel pressure tester in the fuel line to monitor the fuel pressure.
I think your getting frustrated. Some things require a lot of testing to find an answer especially this way as I don't have access to the vehicle.
Another trick I use is a small 12 volt buzzer that I tie into the fuel pump battery feed at the rear fuel pump connector and it constantly buzzes until battery voltage to the pump stops. I use several types of these buzzers and I can be working on another vehicle and still listen to the buzzers on your vehicle.
There are numerous tricks to the trade, But I have to HAVE the vehicle.
autohelp
autohelp
AnswerYou staed: "I'm getting spark but no fire".
My answer: The above makes no sense.
You stated: "So dosen't that take us to the throttle body
itself?
NO it does not.
The only things on the throttle body are:
1. The TPS. Failure would cause the CHECK ENGINE LIGHT to
illuminate But would NOT prevent fuel delivery from the
injectors.
2. The Fuel pump pressure regualtor. Could cause the
vehicle NOT to start But I have ONLY seen 2 or 3 faulty
in over 20 years.
3. 2 fuel injectors. Chances of BOTH injectors failing at
the same time is 1 million to one. I also have only seen
a handful of faulty injectors and even then oNLY ONE
would be faulty, NOT both..
4. The IAC valve. Would NOT prevent the vehicle from
starting.
OK, I went back into my old notes and came across a possibility and the test is VERY SIMPLE.
When the truck stalls out and won't start can you physically see ANY fuel being emitted from the injectors when you are trying to start the vehicle ?.
If you see fuel being emitted from BOTH injectors during cranking do not proceed to the next steps of this procedure.
If you do NOT have fuel being emitted from BOTH injectors proceed to the next steps.
The injectors should have battery voltage on only ONE of the 2 wires of each injector electrical connector at ALL times when the ignition is in the ON position.
Therefore, You can use a 12 volt test light for this simple test.
1. Unplug BOTH electrical connectors on both injectors.
2. Turn the ignition to the ON position.
3. Locate a suitable ground source and attach the test light alligator clip to this ground source.
4. Probe each disconnected wires in BOTH injectors and you should have battery on one terminal of each connector as long as the ignition is in the ON position.
5. Identify which color wire in each disconnected electrical injector connector that has battery voltage.
6. Do not re-attach the electrical connectors to the
injectors.
7. Detach the alligator clip from your ground source and attach it to the other wire in each disconnected electrical injector connector wire that does NOT have battery voltage.
7. While watching the test light crank the engine and you should see the test light flash ON and OFF as you crank the engine.
8. Repeat the same procedure on the other injector.
Let me know your results.
Since the injectors have battery voltage at all times with ignition ON, The ground side of the injector is PULSED by the ECM. I have run across several ECM's that when they got hot the ECM failed to pulse the ground side of the injectors. I have proven this by lowering the ECM down onto the floor board and with the vehicle's engine running, I would use a hair drier set on low or medium and heat up the ECM to see if the engine quit running and then I would proceed to the above test light procedure.
If The test light did not flash ON and OFF this tells me that the ECM is TEMPERATURE SENSITIVE and requires replacement.
Thus, Problem solved.
If a road trip becomes necessary, I will have you obtain the part # of the ECM from the white sticker on the ECM casing to be sure that one is available in your area in case the tests prove that the ECM is the fault.
Hang in there, Knock on wood, I have YET to find a vehicle that I could not diagnose the problem and resolve it before I left provided the necessary parts were available.
ALWAYS keep in mind, Just because a part is NEW does NOT guarantee that it works. I have taken brand new parts right out of the factory sealed box that were faulty on many occassions of which is why I test the NEW component, If possible, Before I install it.
How far away are you from Albuquerque ?. I am seriously thinking about making a house call just to get this truck running properly.
With the high cost of gas, I will only bring the tools and testers that I need and will drive out with my 1986 Chevy Blazer with the 2.8L engine in it and tow one of my small single axle 4x8 trailers and pay you a visit.
autohelp
