General OBD-II EFI Diagnostic methods
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Senior User
Joined: Apr 2004
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From: north central Indiana
General OBD-II EFI Diagnostic methods
My F150 is running fine but now I've got definite issues with my '95 Mustang 3.8 V6. I've been trying to figure out how to diagnose EFI problems on an OBD-II system when the "check engine" light isn't coming on and no codes are being set. The thing runs so rich it drowns the plugs in a matter of a couple minutes or less. I tested the CE light for function (disconnected MAF sensor) and it does work.
I have a Mac Tools ET-97 scanner (a DIYer type of scanner) that can read data streams but could use some guidance as to what to look for. I have a factory service manual on disc but it's geared toward the Ford STAR tool and more upscale generic scanners. Getting a bit desperate so any input will be greatly apprecitated!!
I have a Mac Tools ET-97 scanner (a DIYer type of scanner) that can read data streams but could use some guidance as to what to look for. I have a factory service manual on disc but it's geared toward the Ford STAR tool and more upscale generic scanners. Getting a bit desperate so any input will be greatly apprecitated!!
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Joined: Aug 2001
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From: South Texas
Are you SURE it is fully OBDII ? 95 was a transitional year for the computer system and although it has an OBDII port it also should have an OBDI port under the hood. My son's 95 Mustang with the same engine was so equipped and to test it you need to access it thru the OBDI connector using OBDI testing methods. The 95 GEM computer was a 1 year only model. 96 and up are fully OBDII compliant.
Anyway, I would start by looking at the fuel pressure in the injector rails. A failing regulator could cause it to dump too much fuel into the engine. Some general pressure readings are around 30-35 PSI. Much over that and suspect problems there.
Anyway, I would start by looking at the fuel pressure in the injector rails. A failing regulator could cause it to dump too much fuel into the engine. Some general pressure readings are around 30-35 PSI. Much over that and suspect problems there.
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Thanks for the response Dialtone. Fuel pressure checks out in spec in key-on and engine running tests. Regulator operates properly (pressure increases when vacuum is removed).
As for the OBD-II question, I can only say at this point that I haven't seen an OBD-I connector in the engine compartment, and I had read in a number of different places that the 5.0s were OBD-I and the V6s were OBD-II. This is the first I've heard of the possibility of having both connectors in the same car. I do know that my scanner tells me that quite a few testing modes aren't supported in the PCM. Where specifically under the hood might I find an OBD-I connector? I'll definitely take a closer look for one.
As for the OBD-II question, I can only say at this point that I haven't seen an OBD-I connector in the engine compartment, and I had read in a number of different places that the 5.0s were OBD-I and the V6s were OBD-II. This is the first I've heard of the possibility of having both connectors in the same car. I do know that my scanner tells me that quite a few testing modes aren't supported in the PCM. Where specifically under the hood might I find an OBD-I connector? I'll definitely take a closer look for one.
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From: Louisville,Ky.
It is OBDII. I had this happen. Check the injector plug with a noid light. These are bad about the injector driver sticking open and the injector just stays wide open and dump raw fuel into the cylinder. The noid light should flicker not stay on bright.
The V6 Mustangs went OBD-II in 94, the 5.0's stayed EEC-V until 96. The 94 4.6L Coungar/T-Bird is also OBD-II. In 96, they all went OBD-II
The V6 Mustangs went OBD-II in 94, the 5.0's stayed EEC-V until 96. The 94 4.6L Coungar/T-Bird is also OBD-II. In 96, they all went OBD-II
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Senior User
Joined: Apr 2004
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From: north central Indiana
It is OBDII. I had this happen. Check the injector plug with a noid light. These are bad about the injector driver sticking open and the injector just stays wide open and dump raw fuel into the cylinder. The noid light should flicker not stay on bright.
The V6 Mustangs went OBD-II in 94, the 5.0's stayed EEC-V until 96. The 94 4.6L Coungar/T-Bird is also OBD-II. In 96, they all went OBD-II
The V6 Mustangs went OBD-II in 94, the 5.0's stayed EEC-V until 96. The 94 4.6L Coungar/T-Bird is also OBD-II. In 96, they all went OBD-II
Okay, I'm with ya on the OBD-II, but I don't have any noid lights at this time. S'pose I oughta deal with that issue since everything I have now is EFI. Would the "driver sticking open" as you describe affect all 6 injectors simultaneously?
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Senior User
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From: north central Indiana
Acquired a noid light and checked the signal at #1 injector. Light flashed when cranking engine over so that's not the issue. I've been all over this thing and am out of ideas. I actually was able to locate someone who is willing to come to my place and do the diagnosis. He's trying to build his own business working with EFI type stuff while working a full-time job. Hopefully he knows what he's doing. Guess I'm gonna find out!
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Problem solved! I was fortunate enough to find someone with the proper knowledge and equipment to come to my garage and do the diagnosis. Charged me $35 to hook up his $9000 scanner to it and concluded that the mass airflow sensor was the problem. He found codes that my little hand-held unit couldn't. Replaced the MAF sensor and we're back in business!
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