hesitation worse when A/C on

[cory58]

I'm trying to solve a hesitation problem on my Touring. Threads here on r3v have been helpful, but I haven't found the problem yet.

I noticed yesterday that the hesitation is worse with the A/C on, and wondered if that might help narrow down the potential causes.

Without A/C
Hesitation at WOT, at med to high revs (tach is non op, so don't know exact rpm). Seems to be getting worse over time.

With A/C
Hesitation much worse, at partial throttle and lower revs.

Parts replaced the day I bought the car
spark plugs
cap and rotor
air filter
fuel filter

First noticed the hesitation 5-600 miles after the tune up.

Parts replaced Friday that did not fix the hesitation
plug wires
coil

Any thoughts on the cause of the hesitation?

Cory

[jeffnhiscars]

If your foot is to the floor I'd suspect TPS. The only thing I can think of that the ac would effect is idle which is also related to the tps.

Other than that perhaps a flat spot in the AFM, vacuum leak, fpr or a bad injector.

Let me know if you don't have spares to swap in as I probably do

[cory58]

Thanks Jeff! I'll text you when I'm ready to dig in again.

Cory

[Kershaw]

http://www.r3vlimited.com/board/showthread.php?t=372569

Go through my thread here. I experienced the same issue.

[cory58]

http://www.r3vlimited.com/board/showthread.php?t=372569

Go through my thread here. I experienced the same issue.

Thanks Kershaw. Lots of good info in your thread, but my hesitation is a little different: not only at WOT and no CEL light.

From the thread, it looks like your problem was fixed by the megasquirt, but it seems like you never figured out what was actually causing the problem.

One post caught my attention - if it's fuel related, that would not trigger the CEL.

[Kershaw]

When my hesitation was undrivable, what fixed that was replacing the toothed harmonic balancer. But since that was 1.5 years ago now I can't remember if I was getting CELs with it. But it was at all RPMs and all over the place.

But yeah, I would go through the standard list and start checking and replacing. JLevie experienced an identical issue, he fixed it with a new engine harness after going through 3 used harnesses that were good in other cars. After checking with 3 other engine harnesses, I decided to go that route as well, but they are NLA. So I went to megasquirt. It was a great upgrade.

[cory58]

When my hesitation was undrivable, what fixed that was replacing the toothed harmonic balancer. But since that was 1.5 years ago now I can't remember if I was getting CELs with it. But it was at all RPMs and all over the place.

But yeah, I would go through the standard list and start checking and replacing. JLevie experienced an identical issue, he fixed it with a new engine harness after going through 3 used harnesses that were good in other cars. After checking with 3 other engine harnesses, I decided to go that route as well, but they are NLA. So I went to megasquirt. It was a great upgrade.

Great info. Thank you!

[cory58]

Update: Replaced the O2 sensor and spark plugs last weekend and.......hesitation gone!

Don't know the age of the O2 sensor, so it could have been original (179k miles/28 years). The spark plugs had less than 2k miles on them and looked a lot worse than I anticipated.

[jeffnhiscars]

Update: Replaced the O2 sensor and spark plugs last weekend and.......hesitation gone!

Don't know the age of the O2 sensor, so it could have been original (179k miles/28 years). The spark plugs had less than 2k miles on them and looked a lot worse than I anticipated.

I can see how a bad o2 sensor could easily cause your plugs to foul. Glad you got it resolved.

[g.ruff561]

I'm having the same problem with the a/c on my M42. Car idles fine without a/c on. Switch a/c on and car stumbles, idle drops to 500?600. Recently purchased car with no a/c. PO had broken high side line port. I added new dryer, belt, high side line, vacumn system, recharge.

Highway driving a/c is freezing. Stop and go traffic, car stumbles at every stop. Close to cut off.

I have changed all hoses under intake. ICV has been cleaned thoroughly. No leaks. New intake gasket. Gotta have a/c in Fla this time of year. Any answers...????

[cory58]

Problem Not Fixed!

Update: So after approx. 1,200 miles, the hesitation came back. Something is still destroying the spark plugs, and now I see the pattern. I replaced the plugs again, and the car runs great. New plugs last about 800 - 1200 miles before the hesitation begins. The only additional changes since last time are a refurb AFM (from Bav Resorations) and cleaned ICV.

Here are pics of the plugs that were in the car for approx. 1200 miles, in order from 1-6. Before I start throwing money at new parts, I'm hoping to get some opinions on what might be causing the plugs to get destroyed so quickly. Any thoughts would be greatly appreciated.













Thanks, Cory

[fastbub]

Burnt Valves or possibly valve adjusted too tight letting valves hang open and cooking your plugs.

Worth a look, I don't think this throws a CEL. Others may correct me if I am wrong.

[jeffnhiscars]

If you haven't freshened the injectors (and o rings)I still have the ones I pulled from my cabrio that were working fine. May be worth trying

[cory58]

Thanks Jeff! I will text you.

fastbub - Thanks for the suggestion. I have no experience with burnt valves. If that's the problem, would the car run as if nothing's wrong with new plugs? Any other symptoms of burnt valves?

Thanks, Cory

[gearheadE30]

If you're burning valves, you'd have hard starting, rough idle, and a myriad of other issues beyond a WOT stumble. That said, checking the valves is easy and if it hasn't been done, you should check them.

You may want to rent a fuel pressure tester and make sure you're maintaining pressure at WOT, just to check that one off the list. Also might be worth looking at the cap and rotor to see what kind of shape they are in.