joccomo

I have had this problem since the day I bought my 964. Downhilll or flat, full tank or empty , hot or cold.. I have found that it happens most when using the engine to pull down your speed while in gear. Gotta be a DME issue.. some kind of brain fart. Someone has to have the answer. Repost if this thread dies. This is the perfect question to get answered on this site.

Heirsh

I don't particularly care for beating a dead horse, but shortly after thinking I found the solution Nessie reared its ugly head again. Although the problem is far far less trouble than it was with that broken vacuum line, the problem is still there.

Specifically the problem happens when you press the throttle enough to bring the car off of idle, but not far enough to really open the butterflies. This is a slight downhill attitude. As mentioned in previous posts, a quick full throttle to trigger the wot switch cures it (closed loop, ignores the ox sensor adjustments). I still whole heartedly believe during this situation the car is running either way lean or way rich and the system tries to compensate. I realize this is an unpopular opinion, but it fits my observations. When you trigger wot it immediately reverts to normal settings and thus is fixed.

I have a problem in my AFM that the resistance surface is cracked near the low angles. Seeing as low demands are where I am seeing the problem, could this be the problem. I do notice when checking the afm voltage outputs that it doesnt work like I would expect it; it doesnt go up smoothly, and in fact, drops quickly for a short throw then goes back to climbing. This seems to me that it could be the problem. I did tinker with the afm to get the arm to ride on a slightly different track, but it did not help (yes I did my best to adjust the 0 properly, which miraculously I think i did). Anyone ever repaired one of these things?

Anyone have any thoughts? Besides my annoying squeeling pig (the brakes) which I intend to fix this weekend, this is the last serious annoyance I have to cure. Please o please help me if you can.

Eric Kessel

I haven't had my "bucking" downhill problem since I replaced my fuel pump....... is it related? I don't know...............

JasonAndreas

Have you checked out F.R Wilk's website?

Heirsh

Wow, nice site. No Jason, I have not seen it before. I'll have to pull mine out and have another goa t it.

Funny thing is that it details how to get it to run on fresh track and it is what I did, but I still had it dip as I was opening (the voltage). So I'll take another look at it. Perhaps this is my problem. Sure isn't good in any case.

Thank you immensely for the link. You are a true asset to Rennlist.

DarrylH

This is an interesting thread. My car has done the power-loss-on-downhill thing since I got it. It also has just the faintest DROP in rpm if you feather into the throttle from idle, presumably as the idle switch leaves the party. I assumed both of these were "just the way it is" and have learned to drive around them . Neither my mechanic nor I have been able to see anything apparently wrong in the AFM. Better have another look...At one point I was irritated enough that I was going to replace the AFM on speculation but at ~ $1800 - nobody else drives my car anyway!

Heirsh

1800? holy cow. vertex has it listed in a catalog of theirs new at 399. Prob 9mo old catalog havent checked lately.

DarrylH

Well, I dunno, I just asked at the dealer's parts counter when I was in one day for something else. After they picked me up off the floor, I thanked them politely and left...and never looked any further. If I knew for sure it would solve the problem, it might be worth the 400...but I'm just not convinced. My old AFM looks pretty good, really.

peterC2S

I've had the same problem since I had my current C2. When I had it in for its last service my mechanic swapped out the AFM for another he had in the shop to ty and isolate the fault. With the replacement AFM in the symptons completely disapeared so it seems like the AFM is the issue. Exactly how...? That's the next problem to try and solve.

Cheers
Peter

DarrylH

Well, that sounds promising. I think I'll try one more R&R and if no go, look for the most reasonably priced replacement. Heck, it's got 210k km on it, wear alone would be enough...Thanks for your experience.

peterC2S

Darryl - after identifying that changing the AFM made a difference I had pretty much decided that I'd have to install a replacement as my mechanic couldn't offer a cost effective way to further diagnose the fault. ie. he could spend a lot of time and my $ with no guarantee that I wouldn't have to replace it at the end anyway.

Now I've noticed that the problem has been far less pronounced since the original AFM has been put back. The downhill hesitation and power loss both occurs less frequently and when it does it is less severe. Prior to swapping the unit out it could be quite a sudden loss of power and just as sudden when it came back on. Now its more of a hesitation or stutter than a complete loss - and I can go for several days without seeing the symptoms.

Frustrating! For reference I have a 91 C2 tip with 130,000km, originally delivered into Asia and then imported to NZ. It seems that the mix of cars with this issue are spread pretty far and wide - US, UK and ROW.

Peter

DarrylH

Oh, man, don't you just hate that. I thought at one point it was fixed, cleaning & tidying only, didn't happen for some time, but then, sometimes it was like that anyway, very intermittent. Then it came back. So I don't know whether there was any improvement in the first place. And I hate throwing parts at a problem without a firm diagnosis. So we're in the same boat.

Heirsh

guys, if you trigger wot during the problem will it go away?

peterC2S

By 'wot' you mean fully depressed throttle? If so, then yes it clears the problem but then the more aggressive I am in applying throttle the more violently the power seems to come back on after 1-2 secs. Also, because it tends to happen on the same inclines on my daily commute, its usually in heavy to moderate traffic and the effect of triggering wot would be to give the car in front a good nudge!

I'll see if I can replicate the problem on a clear road and report back.

Peter

Heirsh

yeah, I don't like to do it either, but if that clears yours thats one more thing we have in common. My next test, if I havent solved it (cross your fingers that I have) is disconnect the ox sensor. It would add merit to my thoughts that the mix is wrong during those times and altering the mixture rather drastically. W/o the ox sensor it can't alter the mix. Of course, that means during those times the mixture would be wrong. Just more info for the puzzle.

I'll find out tomorrow where I stand.

I've even thought about wiring up a switch inside that triggers the wot switch to clear this problem. I guess its a way, but it would be so much better to just fix it.