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Technican: Hello, What engine do you have, please? Is the fuel filter in need of replacement? Have you considered testing to see if the fuel pressure is okay and the fuel rail retains pressure after the engine has been shut down?
When the condition is present, have you checked for spark? Does priming the engine through the intake help?
Please advise.
Owner: I have the 4.0 V6 engine. I changed the fuel filter not long ago. It has never acted as though it were starving for fuel, nor have I smelt or seen a leak. It will start right up one time and not the next. It runs pretty good once it starts, but it has started geting to where it idles a little ruff. I'm thinking one problem might the throtle position sensor.
Technican: All right, I'll gather some info from the Mitchell 1 Auto Repair Data Base for a "No Start" condition. Have you tried disconnecting the battery negative cable to clear any code history and reset the computer? 30 seconds ought to do it.
When it cranks, but does not start, do you cycle the key to "Off" before you retry to start? That step can be important and I recommend a 10 second pause between attempts to start so that the computer gets a "new" look at the sensors involved.
I can't get to the info I need until tomorrow. Is that okay with you?
I'm not ready to think about the throttle position sensor as a cause yet. A vacuum leak is often cause for a rough idle when no misfire is present.
Technican: Do you have a fax number? Would a cover sheet be needed?
Technican: Hello, any change in the status of this question?
Just checking in with you,
Owner: Don't know if you got what I just sent you. This thing allowed me to write and then ask me to log in after I sent it. I went about 3 weeks with out a problem. I have taken the truck to Las Vegas and back with out a problem. It does start missing at idle from time to time. It is a missfire. All of the sudden once I got back here to Barstow I get in and it won't start. Let it sit for awhile and it kicks off. Do you think that it might be the coil pack?
Technican: I would hope that when the "cranks but no start" condition is present that diagnosis would verify fuel pressure is correct and that there is no spark.
I would want to use a scanner (not a code reader) and look for crankshaft position sensor signal. If the signal was okay I'd lean toward an ignition module.
During the occassional misfire I'd be looking to flush injectors if spark was proved to be normal.
Coil failure is still a posibility but not really suspect yet.
Owner: I have a code reader, but find it difficult to use. I think that I had rather use a volt meter so that I could see the swing of the needle.
I understand where you are coming from on both the crankshaft position and the module. It had always been my understanding that when the module was going bad that it would warm up, the circuit would open, and the engine would die. It's not doing that, it does seem to miss more the warmer it gets, but it does not die. It just won't start again once you turn it off. Crazy thing about it is that it just went 2 weeks without it happening, but now it's happening allot again. Seems to never be a problem first thing in the morning. I take it that if it is the crankshaft sensor that it is out of time and therefore won't start. I know that the module tells the coil when to energize and the plug fire. My book says that two cylinders fire at the same time, so I take it that for a six cylinder that there are three coils in the coil pack. I was thinking perhaps a coil had become week and perhaps opening.
As far as fuel, I doubt that to be the problem, although the seal on the gas tank filler has gone bad and will not hold pressure on the system. I don't know hom much pressure is depended for fuel delivery upon in these latter model vehicles. By the way is that seal going to be a dealer item?
Technican: A crankshaft sensor can "fail" from radiant heat, cool down and work again and never turn on the Service Engine Soon light or set a code.
I suggested a scanner because a code reader will not display sensor data feedback values.
If however, your meter is a high impedence digital type and can detect ac milivolts, you can set up to monitor the sensor output during the no start condition. You could decide if this sensor is dropping out. It will be difficult on a hot engine.
Fuel pressure should be in the upper 40s psi. The seal you spoke of will likely be a dealer item.
On the six cylinder engine each coil fires two cylinders at the same time by what is called the waste-fire method. If one coil dropped out then two cylinders would be effected. It would still start and run on the remaining four cylinders albeit a ruff running rascal. You may just have one of the two plug wires associated with one particular coil breaking down if the miss is not all that bad. Also, you may have a vacuum leak.
Consider how the heat under the hood continues to build after you turn the engine off. This heat can have the same effect you anticipate the module will have in a driving scenerio that shuts down the engine. But this time the heat builds to the point that the module may be experiencing an open circuit that engine restart is not possible until things cool down.
It's all about duplicating the complaint condition and diagnosing during the presence of symptoms. Takes out the guesswork and limits the number of parts.
Technican: Still need help here?
Owner: Yes Rodger, thanks. I continue to have intermittent problems. I finnally broke down and went and bought another multimeter and did the test yesterday. On the key on engine off test I got 111 twice in a row, then it gave me a 157 twice in a row. The engine on test, it never identified the engine, gave a 111, then 998, then 157, then 998, and then 167. Problem with the 167 is that the computer never flashed the one time to request me to goose the engine for the dynamic responce test. Looks like I must have some sort of problem in the MAF circuit though. I checked for battery voltage to the MAF and it was good. I also did a continuity check and it showed to be good. Notice the 998 came before each of the other two codes. What do they mean by a hard fault? Do they mean a ground?
Technican: When no repairs have been done and you first check for codes one should write them down in order, then clear the codes.
If the engine will start, run the engine until the "check engine" light comes back on. Recheck for codes and anything on the new list that was also on the old list is called a "hard fault" (because it came right back) and the component identified by the code needs diagnosed. Code repairs should be diagnosed from the lowest number (in numerical order) to the highest number.
How clean is the screen on the MAF Sensor? Do the elements look burned or damaged? Here's How To Get Guaranteed Solutions In Minutes
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