| Author | Message | ||
     Greg French (Gregfrench) Senior Member Username: Gregfrench Post Number: 487 Registered: 11-2002 |
After months of changing things, I finally broke down and took it to the garage. They determined that they weren't getting any readings from the MAF, as in, it was dead or something. I searched the archives, but my real question has not been answered there. What should my next step be? I am thinking I should try to clean the contacts. How and where do I do this? The lead on the outside I would guess, but is there anything inside that should be cleaned? (No...I do not have K&N) Hopefully they will test the wires leading to it to determine if they are getting power. If cleaning doesn't fix it, is there anything else I should do before buying a whole new assembly? Thanks. | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1801 Registered: 02-2002 |
Does your garage have the testbook? Do they have the Electonic troubleshooting manual? While I have not run the MAF tests, the operation of the MAF can be confirmed by the testbook, or the ETM method. Also, there are some rumors of poor electrical connections on the connector to the MAF, but I have not found this to be a major problem. There are many ways the MAF can be found to not be commmunicaitng with the ECU, yet the MAF can be good. Before replacing it, confirm the path from sensor to ECU. Then, consider replacing the MAF. | ||
| Greg French (Gregfrench) Senior Member Username: Gregfrench Post Number: 488 Registered: 11-2002 |
Right. I thought it would be something like that. Check the little things first. "It ain't got no gas in it." I gave them my workshop manual. Not sure about the other troubleshooting things. I know when I went to check on it, they had it hooked up to some diagnostic computers. Didn't bother to ask what they were, as they have always seemd to do a good job whenever I have needed something. | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1804 Registered: 02-2002 |
Just don't let them sell you an expensive part until they have convinced you it is in fact the MAF sensor. MAF codes are common. MAF failures are not. Last year, I had a Defender in with a MAF codes... Turned out to be a bad ignition amplifier wiring harness. | ||
| Greg French (Gregfrench) Senior Member Username: Gregfrench Post Number: 489 Registered: 11-2002 |
Right. They are good to me and wouldn't do that. They are just checking it out to try to figure what the problem is, as they are better at that sort of thing than I. I plan on doing the rest of the work once I know what the real problem is. Here's the deal now...They say that they are not getting any reading on the MAF sensor whether it is plugged in or not, and unplugging it does not trip a code. That seems strange to them. Any ideas? What else should I look at? I am picking it up in a few minutes and will be troubleshooting it as good as I can on my own. I just needed them to steer me in some sort of direction, as I had used up all of my knowledge. Thanks again. WWPD? | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1806 Registered: 02-2002 |
Well, I'm kind of shooting in the dark as I don't know what year of vehicle you have, therefor, I do not know what sort of diagnostics the vehicle has and therefor can't tell to what degree the shop can monitor such responses from the MAF. We also do not know for certain what sort of diagnostic computer they have. Personally, I would check to make sure it is throwing a code for a non-responsive MAF. Next, determine if the wiring harness to and from the MAF is intact and continuous. Next, check connections at both ends of the cable. Whoops, I just noticed your statement that it is not throwing a code... Either this isn't the problem, or you have a bigger problem. What year of truck do you have and what sort of diagnostic equipment does your shop have? This may be one of those situations where traditional brute force troubleshooting is called for. Peace, Paul | ||
| Greg French (Gregfrench) Senior Member Username: Gregfrench Post Number: 490 Registered: 11-2002 |
Ok. Here is the latest latest. Sadly, They do not have the right diagnostic equipment, but he said the MAF was working properly. The ECU, according to his tester, doesn't acknowledge that the MAF is there. Here are the codes it went in there with: 1316 1317...both environmental 300- General Misfire 305- #5 307- #7 Also, he said the fuel trim is in the negatives. It is a 97 D1 His idea was that the computer doesn't know there is fuel and air in the chamber, and is not sending a spark to the plugs, causing it to misfire and throw off the environmental sensors. Sound reasonable? What should I do next? | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1812 Registered: 02-2002 |
Greg: It sounds as though you need a valve job... Pretty typical symptoms. Start running compression and leak down tests, I suspect you will find a low cylinder or two due to the valve being fouled. | ||
| Greg French (Gregfrench) Senior Member Username: Gregfrench Post Number: 491 Registered: 11-2002 |
That's what I was originally afraid of. How would bad valves make it so the ECU couldn't read the MAF? or is that just him not having the right test equipment? How hard is a compression and leak down test? I have access to a compression gauge, but don't have the knowhow. I am guessing that I screw it into the sparkplug hole and start the truck, read the gauge, then move on the the next plug, then compare the numbers, but that is just a wild guess. Please advise. Over. (Chhht) | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1815 Registered: 02-2002 |
The on board diagnostics are only intended to inform us of malfunctions that will result in increased emissions. The MAF works with the other sensors to insure greatest volumetric and stoichiometric efficiency. When the engine misfires due to non-closing valves, unburned fuel is introduced to the exhaust system and the ECU tries to lean the fuel mixture to compensate for what it sees as a far too rich condition. When this starts to take place, the ECU freaks out and starts querying all of the sensors to determine which one is causing the problem. When things get so far out of control (in a statistical sense) that the ECU cannot make heads nor tails of what is happeneing, it can throw multiple and often-times misleading codes. When you stated that the misfire code had been thrown, it alerted me to the likelihood of valve problems. To test compression, one disconnects the coil wire (on most engines... In this case, pulling a fuse may be your best route here) and pulls all of the spark plugs. The tester is screwed into each cylinder, one at a time (D'Oh) and the engine cranked for a given period of time (usually a few revolutions of the crank). Each cylinder is treated identically and pressure readings compared. Any variation greater than 10-20% is cause for further investigation. Chances are you may find that you have a cylinder or two with significantly lower compression. The leak down test (or Differential Compression test) is where one puts the crank in a position that both valves are fully closed, the cylinder is pressurized and the leakage of that pressure is evaluated to determine if the leakage is slow ro fast and then, one decides if it is bad rings, bad valves, etc. Peace, Paul | ||
| Greg French (Gregfrench) Senior Member Username: Gregfrench Post Number: 492 Registered: 11-2002 |
Paul...I have said it and read it before, but you really are THEE MAN! Thanks! Any idea which fuse I would pull? (97...No distributor) How do I pressurize the cyllinder? Do I do that to the ones I have already determined are bad from the compression test? I would like to do as much as I can on my own, but am still learning. You (and others on here)are a big help. I just want to make sure I don't mess anything up worse than it was. | ||
| Reed Cotton (Reedcotton) Member Username: Reedcotton Post Number: 224 Registered: 01-2003 |
Paul- "The on board diagnostics are only intended to inform us of malfunctions that will result in increased emissions. The MAF works with the other sensors to insure greatest volumetric and stoichiometric efficiency. When the engine misfires due to non-closing valves, unburned fuel is introduced to the exhaust system and the ECU tries to lean the fuel mixture to compensate for what it sees as a far too rich condition. When this starts to take place, the ECU freaks out and starts querying all of the sensors to determine which one is causing the problem. When things get so far out of control (in a statistical sense) that the ECU cannot make heads nor tails of what is happeneing, it can throw multiple and often-times misleading codes. " That is the best description I have yet heard of the ECU funtioning. (I haven't heard the term "stochiometric" since college Chemistry.) The above paragraph should be with any discussion on OBDII codes. I don't know if you wrote this yourself, or was just passing it along, but GOOD JOB!!! -Reed | ||
| Paul T. Schram (Paulschram) Senior Member Username: Paulschram Post Number: 1823 Registered: 02-2002 |
OK, first off, chances are that if you find a bad cylinder from a compression test, you can probably stop there (I'm surprised SOMEONE hasn't already jumped in and told you to pull the freakin' heads:-). I made the pull-the-fuse comment as I knew you had a distributor-less truck, but I don't know which fuse, not having a manual handy, sorry. When running leakdown tests, one needs an air compressor or other source of compressed gas. If a compression test proves a cylinder bad, most folks would not do the leakdown test as the compression test may have proven their fears to be founded. To be honest, if your truck seems to run well, I'd not be too worried about tearing into it. But, if it is running poorly, I believe I would give serious consideration to pulling the top half of the engine down and having the heads done. Glad I was able to help, even if I didn't say what you wanted to hear. I call 'em as I see 'em. |
