Idle problem and stalling 1998 F150
Thread Starter
Junior Member
Joined: Mar 2009
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wiring diagram F150 1998
This is driving me nuts !
The PCM is new, the MAF is new the ground is ok and I have 12.8V on the MAF aswell.
There should be 4.5V on one wire and this isn't there.
PCM doesn't provide it and neither does the MAF.
Mechanic said once that he measured on another Ford car that there was 4.5 on the wire even though it was disconnected from the MAF sensor.
I read on other pages on MAF sensors that there is also an EFI Relay involved and if I see these diagrams the EFI is in between the MAF an the PCM.
So could it be that the EFI Relay would provide the 4.5V ?
I am looking for a wiring diagram of a 1998 F150 (4.6L) so I can see whether that is the case.
Anyone?
John
The PCM is new, the MAF is new the ground is ok and I have 12.8V on the MAF aswell.
There should be 4.5V on one wire and this isn't there.
PCM doesn't provide it and neither does the MAF.
Mechanic said once that he measured on another Ford car that there was 4.5 on the wire even though it was disconnected from the MAF sensor.
I read on other pages on MAF sensors that there is also an EFI Relay involved and if I see these diagrams the EFI is in between the MAF an the PCM.
So could it be that the EFI Relay would provide the 4.5V ?
I am looking for a wiring diagram of a 1998 F150 (4.6L) so I can see whether that is the case.
Anyone?
John
Junior Member
Joined: Mar 2009
Posts: 13
Likes: 0
John,
I also have a 98 with a 4.2 L V6. I looked at my schematic and there is nothing in between the MAF and PCM. That 4.5 V your mechanic mentioned may be the normal open loop reading taken across the PCM with the MAF disconnected but I can't find that value anywhere. I really think your problem is in the two wires in your harness from the sensor to the PCM . I might suggest you look at your harness carefully for any broken insulation or split wires. You have changed the PCM and the MAF so I really believe your problem is in the harness. Those kind of problems can drive you crazy and can be hard to find.
Perhaps disconnect the harness from both the PCM and the MAF and take some resistance readings in each wire to make sure it isn't open and then check between the wires to see if there is a short between them. You may also have a short to ground in one of those wires.
I also have a 98 with a 4.2 L V6. I looked at my schematic and there is nothing in between the MAF and PCM. That 4.5 V your mechanic mentioned may be the normal open loop reading taken across the PCM with the MAF disconnected but I can't find that value anywhere. I really think your problem is in the two wires in your harness from the sensor to the PCM . I might suggest you look at your harness carefully for any broken insulation or split wires. You have changed the PCM and the MAF so I really believe your problem is in the harness. Those kind of problems can drive you crazy and can be hard to find.
Perhaps disconnect the harness from both the PCM and the MAF and take some resistance readings in each wire to make sure it isn't open and then check between the wires to see if there is a short between them. You may also have a short to ground in one of those wires.
Member
Joined: May 2025
Posts: 64
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From: New England
I think my 1998 V6 is showing early signs of this issue. RPM drops sometimes at a light, then returns to normal fairly quick.
Other day I let is sit in the driveway a few days and when started it sounded like it was going to stall, but recovered quickly.
She has 100K miles, not sure when the last tuneup was.
Other day I let is sit in the driveway a few days and when started it sounded like it was going to stall, but recovered quickly.
She has 100K miles, not sure when the last tuneup was.