Missing At High Speed
 

My car is missing at high speed. I am not sure if it is electrical or fuel related as it only happens at higher speeds.. 65+
Ive replaced fuel filter and have run Chevron exclusively and used a bottle of Techron to no avail. Has new plugs, air filter and cap, rotor. Any ideas?
Starts to crap out at 70 and then feels (if I floor it) like one cylinder is kicking in.

don't go fast

Need to check the sensors. Have to do the front axle on the wifes car tomorrow morning.

what rpm's are you experiencing this at, and does it always occur at the same rpm's or does it vary?

Regards,

my tach is non op. Happens when I am cruising in 5th gear

That would be... like 1800 RPMs? I'm not sure...

I believe fourth gear at 60 is 2200 RPMs... ?

I'd want more details about your problem before I could make anything more than suggestions, but I'd start with the simple stuff first, make sure the plugs/wires/cap and rotor are in decent shape, and make sure that the fuel filter is fresh. You'd be amazed at how often folks (including plenty of pro shops) head straight for the most difficult, complex and expensive repairs first, before ruling out the easy stuff.

Post more details and we'll see if we can't help narrow it down for you. For what its worth, I doubt its fuel related, or I would think you'd feel it more than just at highway speeds.

Regards,

Broken tach. Forgot about that. Disconnect it and see if that stops the missing.

Please review my original post. covered those points-

Yeah! Even replaced the radiator! Still misses.

Disconnect the bad tach and report back.

um.. oops! my bad! I don't know how I missed it...

SoCal, is it due to a function of the upshift light that you are suggesting he disconnect the tach?

Regards,

His tach jumps around about twice per second. All early 944 tachs connect directly to the coil wire from the DME. Bad tach could be shorting the coil wire to ground.

If Gordon's tach was working correctly I wouldn't have questioned it.

Ahha!

updated:::
Replaced tach and voila, no more missing at high speeds!!!
I dont quite understand it but for some reason the non op of my tach affected the running of my car...Strange!!

Not strange. Tach and coil have same wire in common. Bad tach = bad ignition.

once again ure da man so cal - great diags and fix - taking my hat of 2 you so cal

Don't applaud -- just throw money!

Actually I've been working with Gordon on this for weeks. Forgot all about the flaky tach.

MANY thanks to Hugh for the help!!

you da man !!!!!


now why do I miss at 4500 in 5th after accelerating rather quickly through the gears, as it hits 4500, it blogs momentarily.

I would say the speed is about 60-70. It only does it from dead stop up through gears. Also, I'm runnin 87 gas and the FQS is back to position 0.

any thoughts ??

Should I move the FQS for 87 octane ??

Vacuum leak or air flow sensor or both. Check the large rubber duct to the throttle body.