3.2 Engine Surge - Ideas??!!??

[Don Plumley]

Hi - My '87 (3.2 DME) has developed a small surge/hesitation under acceleration. Usually noticed in the 2-3 shift between 3.5K and 5.5K RPMs. Happens under 1/2 to full throttle, nothing under constant speed. Varies from subtle to a small yo-yo feeling - but I notice it, and it's annoying. Have Andial chip. Could try to provide more detail about what this feels like.

A few thoughts about what's been done already (all by PO's ):

6/94 17K miles - Head temp sensor
...
9/97 50K miles - fuel hose assy
1/99 60K service - clutch, O2 sensor checked, fuel filter, plugs, dizzy cap & rotor.
7/01 65K miles - Techron

So what are the likely culprits? I was thinking O2 sensor, maybe the DME relay. Or is it just cr@ppy SoCal gas?

I'm trying to avoid the "replace this, and if that does not fix it, replace that" shade-tree mechanic process. Any thoughts appreciated.

Don

[stlrj]

It could be something as simple a bad spark plug, a loose spark plug connector, a clogged injector, intake manifold vacuum leaks, bad ignition cables, or air flow meter CO out of spec.

I have a hunch that it has something to do with ignition if it happened suddenly.

Joe

[marcesq]

Don:

Does it happen once the car gets warmed up, or all the time??

I just went through a similar problem, but my surge/hesitation (actually more like a bucking bronco at times) only occured when the engine was hot.

Thanks to Tony Kelly (APKhaos) the problem was determined to be the Air Flow Meter. We compared the change in resistance while opening the barn door on pins 2 & 3 and my AFM was very different than Tony's.

Then we swapped out the AFM from his 3.2 and that was all she wrote.

Of course the above is not to the exclusion of the items listed by Joe.

Good luck.

[Don Plumley]

Does it happen once the car gets warmed up, or all the time??

Marc - I don't really run it over 4K until the temp is up, so I can't say if it is temp related.

Joe - thanks for the list; guess I'll still be guessing.

And This Thread points to a temp sensor, could mine have gone bad again afer 40K miles?

How do I diag intake manifold vacuum leaks?

Thanks guys.

[stlrj]

Don,

For vacuum leaks, spray some carb cleaner at the base of your intakes while at idle. If your engine smooths out at any point, you found your vacuum leak.

Cheers,

Joe

[Rick Lee]

This is shot in the dark. I had really bad intermittent hanging idle a few months back. One day at a NoVA fun run, we had about 4 Carreras lined up together with the decklids open. I looked at each one with cruise control and noticed the difference between theirs and mine was a small zip tie missing on the cruise control cable where it threads through the throttle butterlfy or whatever that thing is called. I thought I was jury-rigging it, but the others had it too, so this is almost a factory fix. I always carry zip ties with me and had it fixed in under 30 sec. And it really worked too. The cable was just flopping around and getting hung up in there until I stabilized it with a zip tie.

[stlrj]

Have Andial chip


This might be a big hint that we may have overlooked...you might just want to put the stock chip back in.

Stock chips need to address driveability, emission and fuel economy concerns whereas performance chips are more concerned about one thing...zoom.

Joe

[Don Plumley]

Thanks for the ideas:

Joe - yeah, it's an idea but since it's a recent (worsening) development (i.e. it ran fine for a couple of years with this chip), it's hard for me to blame the chip just yet. Your other ideas have merit - I'm just trying to avoid replacing all parts until the symptom goes away so I'm more persistent on the troubleshooting.

Richard - Thanks for the shot. I don't see any zip-ties on my throttle cable, and don't see a shot in my Bentley. Do you have a pic of what you are talking about?

I did a search and I posted on the same subject back in April. I just returned from a drive and the condition is definitely worse since then, so something is deteriorating. That leads me to suspect sensors degrading (could be O2, Temp, Airflow meter) or maybe a worsening vacuum leak. I guess.

Unless anyone else (John, Roland?) has any insights, looks like me and the ohmmeter will be visiting sensors...

Thanks!!

Don

[Rick Lee]

Don, you do have cruise control and it's connected, right? If so, the cable runs from the cannister on the driver's side behind the fuel filter and into the butterfly and is held by a plastic bolt inside a square, bronze colored metal arm that is mounted onto the throttle housing - sorry I don't know the proper names here. Anyway, just on the rear (toward front of car) side of that bronze colored square thingy should be a small zip tie around the back of the plastic bolt. It acts as a shim or spacer to keep that cable from flopping around inside the bronze square thingy. If it flops around, for some reason the idle hangs real bad. BUT it only hung up when my car got hot. We took that cable out when we dropped my engine and neglected to replace that zip tie, which became immediately noticeable on the first test drive. There is a phot of it here somewhere. Someone posted it and had their finger pointing to it and it was a 3.2 Carrera. I have to leave now, but will check when I get back later tonight.

[Don Plumley]

Richard,

Yes I have cruise and it's connected. An image is attached. I did a quick search on the BBS and found the Thread you mentioned.. Your technical description is right at my speed level. I think the white arrow in the photo is pointing to black plastic bolt in the the aformentioned square thingy?

I guess I can see that a zip tie might help the whole assy from backing to the rear of the car, but mine is in pretty snug and does not appear to interfere with the throttle action. I'm also not really having a hung idle problem as you described though. Any chance this could be a prematurely wearing out clutch?

While you are gone I think I'll check out the various sensors that I can get an ohmmeter on...

Thanks!!!

[Lucky]

Don,

Do you have a cat bypass and/or sport muffler? My own personal experience with a Weltmeister chip is that with a free flowing exhaust the O2 sensor does not work well and fools the chip into leaning out the mixture.

As a diagnostic step, I suggest disconnecting the O2 sensor and seeing if the problem clears up. If you have a catalyst, don't leave the O2 off too long as you may cook the catalyst with a too rich mixture. If the problem does go away with the sensor off, then you have two options: 1) leave it off permanently (in which case you'll want to remove the cat if you still have one) or 2) replace what may be a defective 02 sensor (or there may be other FI problems).

Good luck and let all us other 3.2/DME owners know what you find. Thanks!

[marcesq]

Don:

If you start trouble shooting you might try unplugging the O2 sensor and driving the car so that it gets to running temp. This sensor is the easiest to rule out.

Also, it is my understanding that an alternator that is overcharging reeks havac with the DME.

After that pick your poision. Wish I could be more helpful, but the more I learn about DME the more I find that I don't know.

[marcesq]

Hey Don:

How about that 2 posts at the same time from 2 guys that live within 3 miles of one another.

Not bad for NoVa representitives of Pelican Heads.

[Don Plumley]

Two cheers for NoVa from SoCal!

I think the O2 sensor is sounding more like the culprit. First, it is original (67K miles, 15 years). Second, the cylinder temp sensor was replaced and my quick test showed some nominal resistance from a warm sensor. And Third, when I had the car in the garage, I blipped the throttle wide open from the engine compartment and a spray of (what I assume is) oil came forth. So perhaps that is fouling an otherwise old O2 sensor.

Lucky - so I get the car to operating temperature (with the 02 sensor disconnect) and attempt to replicate the surge condition? If no surge, then this means bad sensor?

I'd be happy to dump the cat with a bypass pipe, maybe in my Christmas stocking?

In the back of my mind, I sure am wondering where this oil spray came from...The car does not consume any oil to speak of, I hope I've not discovered a latent valve seal problem.

Thanks guys (more ideas/suggestions welcome too)!

Don

[Rick Lee]

I'm back now for a little while. That photo is EXACTLY what my problem was and there needs to be a zip tie on the back side of it. I never wudda thunk it myself, except that I saw 4 other Carreras next to mine that all had it. Regardless, I'm not sure that's gonna solve your current problem; maybe just prevent a future one. In your list of maint. performed by PO's, you wrote "clutch". What does that mean? Was the G50 update done? Was the rubber-centered disc replaced with the spring-centered one? If your clutch is original, I guess your symptoms could mean the disc is shot. Try doing some hi revs going up a steep hill and see if it slips. There's also some trick you can do with the emerg. brake to make a bad clutch slip, though I don't know what I'm talking about here. I wish I could drive your car and see it for myself. I'm sure we could narrow it down.

[Rick Lee]

Even if you get a test pipe, you'll still need to run an O2 sensor to keep it from running too rich and killing your plugs. I've heard any VW-3 wire O2 sensor for $25-$40 will suffice in lieu of the bull$**** Porsche/Bosch O2 sensor for $179. You'll have a blast removing your old one. Get some beer and a few things to throw in frustration.

[Don Plumley]

Richard - The clutch was replaced at 58K miles, with the update kit. The Clutch kit is listed on the invoice as 950 116 911 00, don't know if that is spring centered or not. The invoice also lists the Update kit, release fork and needle bearing for what it's worth. Very reputable shop.

I'm hoping that I didn't burn a clutch in 9K miles! Since I don't feel any slipping off the line, but only under high-RPM, full-throttle acceleration, I'm hoping/guessing/hoping that it's some other fuel or ignition related problem.

There's a good thread on O2 replacements, I'm thinking of doing it. The reason I was thinking of a test pipe is I think the cat cooks the left side of the engine. I have a very minor leak (ooze) on the lower left side valve cover, but not on the right so I blame the cat.

Anyway, I'm running out of suspects, time to shoot something.

Don

[expat]

Well I had a very similar surge on my ROW 87.

Put a catbypass and new (expensive( O2 sensor in and now no surge.

Just my experience after a good 12 months of yo-yoing down the road.

Cheers
Mark

[Don Plumley]

I retested the Air Volume Sensor in situ and the resistance started at 500 ohms and moved towards the 1K mark. Perhaps my taking it off and banging around broke off some carbon or something - or you can't measure it accurately when it is upside down on your workbench.

So I disconnected the O2 sensor and took some spirited runs. Engine purred up to redline without hesitation. Ah Ha!

To verify, I reconnected the O2 sensor - seemingly no more hesitation. Hmmmmm. Wonder if the act of disconnecting and reconnecting the sensor helped anything?

Now I don't know if it is fixed, or if it is now an intermittent problem. Oh well, I guess that means I need to drive it a bunch more up to redline to know for sure.

Thanks for all for your help and ideas.

Don

[Don Plumley]

I think I broke the air flow meter trying to see if it was not working right. So I put in a remanufactured unit.

Still surging...It's now beyond my abilities.

Hergersheimer's looked it over, checked the fuel delivery system (all is well there) and found - get this - a bad spark plug. According to Mark, it was failing internally, something they picked up on their ignition analyzer. No doubt something I could never have found. CO was a little low too.

The car purred like a kitten and roared like a tiger! It sure is nice to get rid of that surge. Now I'm off to drive it up to Pelican!

Round of applause for Hergersheimer's in Lake Forest - Thanks John, Mark, Laura and Tim. Great Shop.

Thanks to all for your ideas and support. A new failure mode to add to the list.

Don