Hi.
My name is Dick Streever, I am new to this forum and new to the mustang world. I bought a nice clean 91 LX, 5 speed, 5.0 last fall that I am converting to a track car for HPDE, AutoX and maybe a time trial or two. I have been running a 2019 Miata the last few years. Have been enjoying AutoX and track events but can't progress since I am too tall to get under a roll bar in my Miata.
I am having a problem under wide open throttle and hoping a 5.0 guru can point me in the right direction. Car runs great, has lots of power except under WOT. I start out great and when I get to about 3500 rpm the engine starts to miss and buck, almost like it is getting into the rev limiter. If I back off on the throttle a little the miss goes away with ok acceleration. I don't get a check engine light when this occurs.
The car has 150,000 miles, the original engine and all the factory smog equipment. Air intake is factory with a new drop in K&N air filter. Here is what I have done so far and the results:
1) Replaced plugs, cap and rotor with motorcraft parts - no change
2) Replaced the fuel filter with motorcraft filter - no change
3) Found the hard plastic vacuum line loose on the top of the air (smog) pump. Used a flexible rubber hose to reattach to the pump. - problem went away.
4) Drove the car again and problem returned. Found 2 broken hard plastic vacuum lines broken at connector by rear of engine on passenger side. Repaired broken lines with flexible rubber hose. - problem went away.
5) Drove car again and problem returned but at about 4500 rpm instead.
6) Replaced the ignition coil with Motorcraft coil - problem went away.
7) Drove car again today - problem returned, at 3500 rpm.
Wonder if anyone has any ideas and how to troubleshoot? Don't want to replace parts that aren't needed. Mystified as to why it seems fixed and then comes back. Starting to think it might be fuel related?
I have spent my life in technical positions, including some vehicle maintenance. I have a good understanding of how things are supposed to work and good troubleshooting skills, just not the experience (yet) with this car and engine. I have looked up this problem on other mustang forums and am at a loss. Hope someone here can help.
Thanks in advance for any hints.
Dick
My name is Dick Streever, I am new to this forum and new to the mustang world. I bought a nice clean 91 LX, 5 speed, 5.0 last fall that I am converting to a track car for HPDE, AutoX and maybe a time trial or two. I have been running a 2019 Miata the last few years. Have been enjoying AutoX and track events but can't progress since I am too tall to get under a roll bar in my Miata.
I am having a problem under wide open throttle and hoping a 5.0 guru can point me in the right direction. Car runs great, has lots of power except under WOT. I start out great and when I get to about 3500 rpm the engine starts to miss and buck, almost like it is getting into the rev limiter. If I back off on the throttle a little the miss goes away with ok acceleration. I don't get a check engine light when this occurs.
The car has 150,000 miles, the original engine and all the factory smog equipment. Air intake is factory with a new drop in K&N air filter. Here is what I have done so far and the results:
1) Replaced plugs, cap and rotor with motorcraft parts - no change
2) Replaced the fuel filter with motorcraft filter - no change
3) Found the hard plastic vacuum line loose on the top of the air (smog) pump. Used a flexible rubber hose to reattach to the pump. - problem went away.
4) Drove the car again and problem returned. Found 2 broken hard plastic vacuum lines broken at connector by rear of engine on passenger side. Repaired broken lines with flexible rubber hose. - problem went away.
5) Drove car again and problem returned but at about 4500 rpm instead.
6) Replaced the ignition coil with Motorcraft coil - problem went away.
7) Drove car again today - problem returned, at 3500 rpm.
Wonder if anyone has any ideas and how to troubleshoot? Don't want to replace parts that aren't needed. Mystified as to why it seems fixed and then comes back. Starting to think it might be fuel related?
I have spent my life in technical positions, including some vehicle maintenance. I have a good understanding of how things are supposed to work and good troubleshooting skills, just not the experience (yet) with this car and engine. I have looked up this problem on other mustang forums and am at a loss. Hope someone here can help.
Thanks in advance for any hints.
Dick
