Ok, so I've got a high RPM miss w/ my 89 hatch. It's an 89 hatch, 306, blah blah. It seems like when it's cold it misses quite a bit, but when it's warmed up it still misses, but less. 99 percent of the misses are at highter rpm ie 3k and up, but its not consistant. I've gone over alot of stuff, and don't really know where to go now. Plugs, wires, cap, rotor, PCV valve/filter, coil, all new... It' does have 10 year old O2's in it, and original TFI module, but I'm sick of shooting in the dark. Any ideas? Thanks...
Misfire at high rpm...help...
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JChalfan
Member
I got a faulty cap and rotor from a parts place once for a 5.0. Looked perfect, nothing wrong visually, but I had a high RPM (3k+) miss I couldn't figure out. Replaced the cap and rotor with Ford parts, and the miss went away.
Did the miss start after you changed something?
Have you checked for codes? Just because the check engine light isn't on doesn't mean there aren't stored codes in there...
Good luck!
Jeff
Did the miss start after you changed something?
Have you checked for codes? Just because the check engine light isn't on doesn't mean there aren't stored codes in there...
Good luck!
Jeff
Well, the miss started kinda after I did an intake gasket on it, but It sat for like 3 months inbetween. Yes, the check engine light is on, but I can't pull codes. I used an NGS and it won't allow me too, some error message kept comming up, I tried to flash the codes out and that wouldn't work either...
Had the exact same problem. Replaced everything you said, plus the dizzy. Turned out to be a bad coil, and a bad replacement coil from the parts store. Spark should be nice a BLUE, not orangish yellow.
onefstsnake
New Member
The same problem that keeps you from pulling codes probably is causing your miss. The signal ground for all the sensors is the same wire that is used to help dump the codes.
Computer will not go into diagnostic mode
How it is supposed to work:
The black/white wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the
computer into self test mode. Since it is a dedicated ground, it passes through the computer
on its way to the computer main power ground that terminates at the battery pigtail ground.
It should read less than 1.5 ohms when measured from anyplace on the engine harness with
the battery pigtail ground as the other reference point for the ohmmeter probe. What sometimes
happens is that it gets jumpered to power which either burns up the wiring or burns the trace
off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60. Only an
experienced electronics technician can open the computer up & repair the trace if it burns
up and creates an open circuit.
The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering
it to power can produce unknown results, including damage to the computer. The ohm test
simply verifies that there are no breaks in the wiring between the test connector and the computer input.
How to test the wiring :
With the power off, measure the resistance between the computer test ground
(black/white wire) on the self test connector and battery ground. You should see less than
1.5 ohms.
If that check fails, remove the passenger side kick panel and disconnect the computer
connector. There is a 10 MM bolt that holds it in place. Measure the resistance between
the black/white wire and pin 46: it should be less than 1.5 ohms. More that 1.5 ohms is a
wiring problem. If it reads 1.5 ohms or less, then the computer is suspect. On the
computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than
1.5 ohms. More that that and the computer’s internal ground has failed, and the computer
needs to be replaced.
If the first ground check was good, there are other wires to check. Measure the
resistance between the STI computer self test connector (red/white wire) and pin 48 on
the computer main connector: it should be less than 1.5 ohms. More that 1.5 ohms is a
wiring problem
The following is a view from the computer side of the computer connector.
Diagram courtesy of Tmoss & Stang&2birds
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine
Computer will not go into diagnostic mode
How it is supposed to work:
The black/white wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the
computer into self test mode. Since it is a dedicated ground, it passes through the computer
on its way to the computer main power ground that terminates at the battery pigtail ground.
It should read less than 1.5 ohms when measured from anyplace on the engine harness with
the battery pigtail ground as the other reference point for the ohmmeter probe. What sometimes
happens is that it gets jumpered to power which either burns up the wiring or burns the trace
off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60. Only an
experienced electronics technician can open the computer up & repair the trace if it burns
up and creates an open circuit.
The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering
it to power can produce unknown results, including damage to the computer. The ohm test
simply verifies that there are no breaks in the wiring between the test connector and the computer input.
How to test the wiring :
With the power off, measure the resistance between the computer test ground
(black/white wire) on the self test connector and battery ground. You should see less than
1.5 ohms.
If that check fails, remove the passenger side kick panel and disconnect the computer
connector. There is a 10 MM bolt that holds it in place. Measure the resistance between
the black/white wire and pin 46: it should be less than 1.5 ohms. More that 1.5 ohms is a
wiring problem. If it reads 1.5 ohms or less, then the computer is suspect. On the
computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than
1.5 ohms. More that that and the computer’s internal ground has failed, and the computer
needs to be replaced.
If the first ground check was good, there are other wires to check. Measure the
resistance between the STI computer self test connector (red/white wire) and pin 48 on
the computer main connector: it should be less than 1.5 ohms. More that 1.5 ohms is a
wiring problem
The following is a view from the computer side of the computer connector.
Diagram courtesy of Tmoss & Stang&2birds
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine
Ok, so heres an update...jrichter i hope your listening...anyways I pulled codes w/ an NGS and go this 22 63 10(separater code) 22 63 95. Now, the 22 code is a MAP/Baro greater/or less than desired...the 63 code Throttle position circuit out of range, and the 95 code is fuel pump secondary circuit failure...
Lets start w/ TPS... I checked the black wire, and the ground is good. I also checked the orange vref wire and it shows 5.03 volts. Now, on the green wire(voltage signal) theres no voltage, i know the tps sensor is good bc i robbed it off of my other car. Anybody know where I can back track this wire to find my open?
Ok, next code...22 MAP/bp outta range, I have no idea where to start w/ this...
code 95- fuel pump secondary circuit failure...not really sure what this means, i jumped the fuel pump connector at the DLC connector and it held the fuel pump on fine...and it holds 45 lbs fuel pressure...
Any info would be great, thanks, Tom...
Ok, next code...22 MAP/bp outta range, I have no idea where to start w/ this...
code 95- fuel pump secondary circuit failure...not really sure what this means, i jumped the fuel pump connector at the DLC connector and it held the fuel pump on fine...and it holds 45 lbs fuel pressure...
Any info would be great, thanks, Tom...
I corrected the title spelling for search index purposes.
Great information in here. Great work, guys.
Great information in here. Great work, guys.
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