hesitation worse when A/C on

[Seawolf]

Just one other thing.....I looked again at your list of service parts since that is when the problem started, the only thing I can see there that would likely cause a problem is if the fuel filter was installed backwards...might be worth a quick check.

[cory58]

Thanks for the responses! Awesome info. Plugs are correct. Cap and rotor are new. I will start with the compression and fuel pressure, and then report back.

Cory

[Seawolf]

All of those plugs look like they are overheating, assuming you have the correct spark plugs I'd suspect a weak fuel mixture. Maybe marginal fuel pressure or bad/blocked injectors.

An air leak could cause similar plug overheating but you would have a ton of other symptoms so I doubt this is the case here.

It also looks like there are deposits on the plugs, maybe worn valve guides or seals allowing enough oil to foul the plugs, once contaminants bake onto the plugs they can't self clean and will overheat.

A fuel pressure and compression test will eliminate some of the possibles. Though a bad (or wrongly set) TPS, worn AFM carbon track or poor C191 connections are other candidates.

[M_3_X]

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

Depending on how bad they are, yes. It could be only one valve.
I would run a compression test too. A burnt exhaust valve would throw compression down dramatically.

[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.

[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

[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

[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.

[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

[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...????

[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.

[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.

[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!

[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]

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.