Stumbles and stranded - need help! 3.2
 

Guys -

After a lovely drive over to the coast - we headed up Hwy1 to SeaRanch, CA and the car began to stumble badly - engine would cut out and re-engage. Did not die, but did not make for a pleasant trip! 1989 3.2

I'm up here with few tools and fewer skills - and need to go thru some basic diagnostics.

What are the basic diagnostics that I should perform? I've had a snoop-around looking for loose wires, etc. No joy.

Seems happier at lower RPMs, stumbles badly when revving up thru the RPMs, but only sometimes. Starts fine, idles only a bit rough.

I've done the search and become overwhelmed with options - where should I look first?

Thanks for your help - I'd really like to drive home vs. getting towed home over 150 miles!!

TD

Check the DME relay under the seat. You carry a spare, right ?

http://forums.pelicanparts.com/porsche-911-technical-forum/403590-3-2-911-no-spark-condition-seek-advise.html#post3883576

Sounds like a fuel issue.

Just a guess, perhaps a clogged fuel filter. I had a similar experience and a clogged filter was the problem. I comes on slowly but when it reaches a critical point, you have symptoms like yours. The engine begins being starved of fuel when demand becomes greater. Do you know when the filter was replaced last?

Uwanna - hmmm, sounds like that might be it - stumbles like crazy and when I push my foot thru the floor she clears and runs ok for awhile....

I'll look over the DME and see if anything looks amiss / loose.

I don't know when the filter was last replaced....over 5 years is my guess. I've not done it....

I don't have a spare DME. ugh.

keep the ideas coming....

td

Idles fine and stumbles with accelerator sounds like gas but on a Motronic system maybe a really bad spot on the wiper path in the DME itself (not the relay). I can think of worse places to get stuck...was up in the wine country last march...really nice. Maybe one of the Motronic whiz's can chime in?

intermittent?
 

Dear Brain Trust - the thing that I'm not quite grasping is the intermittent aspect of the stumble....acts like it is going to shut down and then catches and is fine. I'm going to pick up the fuel filter this morning, and dive under the seat to have a look at the DME connections....any more thoughts??

Fuel Pump at Load,

Would have to measure fuel pressure while driving for proper diagnosis.

Or throw a 150 dollar part and see what happens

Dont forget to check fuel pump relay connections at fuse box (easy fix)

Fuel pump relay on DME is located IN the DME relay, not at fuse box.

Idle Control Valve need cleaning? Tap it and see if the idle stabilizes.

Speed or reference sensors failing.
Not something you can fix on the road for sure.

Update on findings.....

Wiring appears fine to and from the DME, no mouse nibbles, etc. Pulled off the DME relay end and did not appear corroded. Starts and runs fine.

Fuel pump looks new and shiny....accumulator looks old and grungy.

HOWEVER - I did notice that the negative battery lead was loose, not tight. Would perhaps explain the intermittent nature of the stumble? (its tight now!).

Seemed to happen when the car was fully warm. It was foggy - drizzle - rain at the time, any moisture intrusion that might lead to this conclusion?

Coil seems original.

Is CHT or O2 sensor issue intermittent? DME failure?

thanks for your thoughts?

td

Exactly my dme symptoms. Can't hurt to get another and keep one as an extra if it isn't it, but it is.;)

O2 sensor has very little effect when unplugged. CHT failure is pretty evident in that it will start hard and round REALLY rough. You mention a rough idle. Have you checked IAC and vacuum hoses. I think the fuel pressure regulator has a vacuum line but I don't recall for certain.

When you have a problem like this, it's time to take it in imho. It might save you time and money in the long run.

UPDATE - and a deeper mystery!
 

So - we tentatively headed back from Sea Ranch along the tortuous HWY 1 with a car that was still sputtering and finicky.

We put some epoxy on the underside of the Rotor, (that looks ready for replacement) to keep any stray electricity in check, and after 2 tries to get the right fuel filter we gave that a pass and simply hoped for the best.

Car exhibited similar symptoms - seemed ok at low revs, we just sort of nursed it along the road without putting any load on anything - pretty ok with only to occasional SPUT-SPUTTER.

When we turned inland, things got progressively BETTER. huh? The sputter went away, she was not completely happy but the danger of having her die on the side of road seemed to abate.

The further inland, the hotter and drier the weather got, the better she performed and when we reached Napa Valley - she appeared to run as well as ever! WTF??

QUESTION: what would be effected by TEMP and HUMIDITY that might bring on the cough sputter cough symptoms?

My scheduled maintenance will be:

1. rotor and cap and plug wires
2. plugs, new coil
3. Fuel pump, fuel filter and accumulator
4. MAF sensor
5. Idle control unit
6. Check for vacuum leaks all around
7. DME Unit

AM I MISSING ANY OF THE SIMPLE STUFF?

Thanks for your thoughts on this so far - I'll update as I go along and see if we can find the smoking gun....

happy to be home - without a tow!!

tdSmileWavy

You might fire it up on a dark evening and pop the deck lid to see if you can spot any arcing. Go one by one on your list. If it seems to be moisture related I'd start with plugs, cap, rotor and wires as you list. I thin I'd change the fuel filter not the pump. Not much you can do with the MAF other than test. You can open it up and change the sweep pattern but some don't recommend doing that. Absolutely clean the IACV and check vacuum leaks but I don't know why that would clear up when you get in the dry.
Glad you got it home!

^^^ I think cabmando is onto it. My car experienced exactly the same symptoms when I first bought it - albeit usually only if it was raining / snowing or really wet out. A new set of Magnacor plug wires eventually cured it for me, and I think I replaced the cap and rotor at the same time. I'd go ahead and replace the fuel filter too if you don't know when it was last done, it's never a bad idea.

Might have been a simple problem: a bit of water in the tank. A bottle of dri gas may have cured it right away. I'd put a bottle in now as you may still have some water rolling around the bottom of your tank.

Thanks Guys - we have a plan
 

Gents - thanks SO much for chiming in on my rough running issues - we have a plan and I'll run thru the suggestions and report back.

Cannot thank you all enough - a stressful trip that ended well, but you all helped ease the stress a bit with your suggestions and support.

Cheers - SmileWavy

tom
Dos Lagos Vineyards
Napa, CA