3.2 Engine Stalling - Stumped

[rcaradimos]

Had a Datsun 240z back in "73" when I pushed on the gas hard at 3k it would just die and stall. The fix was a fuel filter; it was not flowing enough fuel under heavy load. Is your filter flowing in the right direction? You said it was new (second one), not sure if it can be installed reversed?? If so the first one could have been installed wrong and the replacement followed.

[rcaradimos]

found this doing a search,

Fuel Filter Arrow

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Just had a fun filled day working on some maintenance items on my new to me 1980 SC ROW. One of these projects was installing a new Bosch fuel filter. The part number of the Bosch fuel filter I removed was exactly the same as the new. The two filters looked identical, BUT, the new filter had the threads reversed, small female thread on the bottom and large on top. Also, the old fuel filter arrows were pointing down when installed, which means the direction of the fuel through the filter would have been going to the Accumulator. This is not how the fuel is supposed to flow, correct? Arrows should be pointing UP from the Accumulator to the FD fuel line.

Soooooooo, I guess the PO had installed the filter the wrong way and all this time my car has been drinking dirty fuel? I don't know how this was possible, unless the factory that made the filter screwed up. Has anyone else seen this? I've been hunting down a few issues around 'loss of power' at higher revs, symptoms like fuel starvation, could this have been the culprit, a reversed fuel filter installation?

Thanks,
Dan
__________________
"The hardest thing to understand in the world is the income tax." Albert Einstein

1980 911 ROW SC Coupe
2008 Mini Cooper S (DD)

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[wnsgc]

Ingo, Loren,

This is good stuff. I'll meet with my mechanic tomorrow and talk to him about these points. Whereas I'm a newbie to the 911 (about 5 years), he's been working on 911's for over 30 years. He's witnessed many problems, but never ran into this one. I seem to recall that both sensors on/near the flywheel were replaced, but I'll double check. If I'm understanding you correctly, there is an RPM-Reference sensor and an RPM-Speed sensor. They're identical but perform different tasks. I'll also talk to him about the various tests you suggest.

More to come soon.
Thanks.

[NeedSpace]

Scott,

I am really sorry to hear about these problems, it is very frustrating, I feel for you man!

It looks like you have covered just about everything. I only have one possible solution. I am leaning toward the last posts that perhaps this isn't an electrical problem but a full starvation problem. Although, it does seem odd that it happens at exactly 3000 RPM (which would make me think electrical as well). I had a similar problem with my old mercedes. It would run fine as long as I didn't give it too much gas. Then it would stall. After about 10 minutes, the car would start and run fine. After about 6 months of messing about, I found the problem. My carbs had an extra filter that after running the engine fast the gunk in my extra fuel filter would starve the carb and cause a bit of a vacuum, engine would stall. About 5-10 mins later, the vacuum would be gone and the car would run fine until I revved it again.

Now, I know you have replaced your fuel pump and your fuel filter, so let's assume it isn't that. Here are a couple of other ideas:
1) When you replaced your fuel pump, did you replace the fuel pump check valve?
2) Have you tried a new fuel accumulator?
3) Have you clean out your fuel tank?
4) When it stalls and you smell the engine, does it smell like fuel? Could it be a flooding problem? Maybe there is some blockage on the fuel return?

I am sorry if these are all over the place, but it seems like you have tried all the usual suspects so I am trying to think a little more out of the box.

Good luck, I hoping for you!

[Laneco]

A 3.2 does not have an accumulator like the CIS cars have.

I would really look into speed and reference sensors. We had one flake out on my husband's car. The car would just shut off - I mean OFF - like a clock. Usually under hard acceleration but that may have been ours. One morning, it just quit cold - we diagnosed it and replaced it (can't remember which it was now). Been perfect ever since.

Just on more random idea for your mechanic. The problem with things that happen intermittently is they are VERY hard to troubleshoot... But you already know that....

angela

[wnsgc]

Thanks to all who've responded. Over the past couple of days, I've attempted to document everything that went wrong and everything we've done to date. As an FYI, we did replace both sensors (TDC and RPM Reference) at the flywheel. We are going to check to see if one or both was bad out of the box. I've also been thinking about the fuel starvation issue. It's almost like there's a blockage in the tank, and when the car needs more fuel (when I press the gas pedal hard), the blockage comes into play, and then when the car stalls out, it takes a while for the blockage to go away (e.g. a ping pong ball in the tank... - bad example, but you may get the idea). We have not cleaned out the tank, nor have we checked the fuel lines, so after we check the sensors, that will be the next steps.

Thanks again and keep those ideas coming. The weather here in central NJ is getting nice and my Targa has been out of commission for way way too long.

[Laneco]

We had a vehicle (not a 911) with a tank expansion line that was pinched. Though they are "sealed" systems on emissions cars, the tank does have provisions for fuel expansion and vent to the engine/charcoal canister. As fuel is used, air displaces the disappearing liquid. Or at least it is supposed to...

This car would run out of gas after you drove it a while. Let it sit, and you could drive it again. Another had a bunch of dirt in the tank that plugged the fuel inlet.

Look, as deep as you are into this? Dropping the tank seems perfectly logical to me. If nothing else, you'll get to clean it thoroughly and it either works or you eliminate THIS as a problem.

angela

[Laneco]

We had a vehicle (not a 911) with a tank expansion line that was pinched. Though they are "sealed" systems on emissions cars, the tank does have provisions for fuel expansion and vent to the engine/charcoal canister. As fuel is used, air displaces the disappearing liquid. Or at least it is supposed to...

This car would run out of gas after you drove it a while. Let it sit, and you could drive it again. Another had a bunch of dirt in the tank that plugged the fuel inlet.

Look, as deep as you are into this? Dropping the tank seems perfectly logical to me. If nothing else, you'll get to clean it thoroughly and it either works or you eliminate THIS as a problem.

Also, the fuel rails on a 3.2 have little valves on them that keep the pressure set - I assume that fuel pressure under RPM has been checked? They have a vacuum port which would lead me to think they are vacuum controlled.

angela

[rcaradimos]

vaccume lines rotted that regulate fuel?

[kidrock]

I've been following this thread with interest, mainly to find out what the solution was. I really feel for Scott.

FWIW, I once had a similar issue....

A little over a year ago last February, we had a 100-year freeze here in West Texas. The temps dropped down to single digits during the daytime for a day, maybe 2. My car is always garaged, but I took her to work during the midnight shift and she was left outside overnight during the worst part of the freeze.

When I went out in the morning to start her, she'd turn and turn but not turn over.

Being in the parking lot, I performed the basic fuel and spark checks. I was getting fuel and spark. I thought that the spark was a little small and weak, but it was spark nonetheless. After the 2nd day in the parking lot, I swallowed my pride and had AAA tow her back home so I could dig into it deeper.

I ran ohm checks and resistance checks on every single sensor and even the coil, and everything came back in spec according to my Bentley. I was so confused and pissed....my tools started magically sprouting wings and my garage walls had a few new holes. My wife, kids and pets, recognizing my issues, steered a large path away from me.

Desperate and out of ideas, I decided to throw money at it. The only things I hadn't replaced on the damn car were the 2 reference sensors and the original black coil. So I bit the bullet and replaced them on Valentine's Day (yes, my wife is still with me).

After installation, I crossed my fingers and toes and proceeded to turn the key. NOTHING. I became so enraged that I made up my mind that I was going to turn the key and not stop until I burned up my starter motor. After about 30 seconds of this, the car coughed like it had emphysema and let out a huge "BANG" and spit out a half cup of unburnt fuel and small, hard bits of carbon and proceeded to start and purr like it never purred before. WTF??????????

So, I don't know if it was the TDC sensor, the speed sensor, the coil, or any combination thereof. It was almost like it gave itself an Italian tuneup.

I guess the moral of the story is, is that you will get it running again....and very soon. You don't have much left to fix or replace. I'm keeping my fingers and toes crossed for you.

Good luck.

[wnsgc]

Greetings folks,

I met with my mechanic this week and we are going to work on my car tomorrow. We are looking or should I say re-examining the sensors (TDC, RPM Reference, and CHT), all of which we've replaced. Who knows, maybe one was bad. Something is telling the injectors to turn off, and then restart after 15 minutes or so. We have replaced the vacuum lines around the fuel system. We got hold of a oscilloscope, so we can test a bit more.

Thanks to all for the kind thoughts.
Scott

[Tippy]

I can't bare to read these threads anymore since I was going through hell myself with my Carerra.........and still are.

I think an oscilloscope will do lots of good. "Lorenfb"s website Systems Consulting IIRC has all the waveforms you need to look for.

Good luck!!

[KNS]

wnsgc,

You have a PM.

[Quicksilver]

I kind of shudder at the quantity of stuff that has been replaced in this process. There is a serious need to test things instead of replacing everything.

Get a fuel gauge and hook it to the test port on the manifold. You just need quick and dirty for the test so use a hose long enough that you can get it out the side of the engine lid and in through the window so you can watch it. Drive it till the car dies. That will tell you if it is anything in the fuel system right up to the injectors. Remember that the injector system is also supposed to retain 20 PSI after the engine is turned off (but that isn't your issue).
Be careful with the fittings. Don't need a molotov Porsche.

If that is good then you are down to electricals.
If you have an oscilloscope hook it up so you can drive in the car with it. If it is 120v then get a power inverter to drive it. Test the injector pulses. One failure that hasn't been mentioned is the plug where the injector harness connects can get loose. I would expect that to cause the car to buck though...

You say you replaced the reference sensor. Did you test the speed sensor as Loren suggested? As he mentioned the reference sensor gets the car started and the speed sensor keeps it running. A number of people have found that adjusting the air gap on both those sensors may be required even on a brand new sensor.

You might look at adding redundant ground wires for all the DME systems. If one of the grounds is less then par that will make it run correctly and then you can chase it farther.

Test the components. If all the components are working then the system will work. When testing things it is a bonus to test from the DME connector because that will test both the component and the wiring harness.

[MikeSchNail]

I read through this entire thread with great interest looking for the end result as I encountered a nearly identical scenario...

Car was an 87 carrera, all original, mileage unknown...

I ultimately captured the loss of the primary signal to the ignition coil, cracked open the DME, inspected the solder joints on the bottom of the board for the ignition transistor, sure enough, they are cracked ever so slightly...

Resoldered the 3 connections, test drove the last three days (approx 20 gallons of fuel) and the fault is apparently gone, as it was quite consistent before hand...

I'm going to make this a regular "inspection point" on any early motronic car with running/stalling issues.

For the record, the speed and ref. sensors, coil, plug wires, AFM,etc, are all original!! Mileage MUST be in the 200K range...

I would seriously consider checking this one both of your previously mentioned DME control units... Best of Luck! Hope this helps

Here is a link to the thread with pics that helped me, if you don't wanna mess with it, I would be happy to check it for you...

DME Bad Solder Joint Repair

[47silver]

Something in your circuit is heating up the dme. You are getting a voltage drop to the dme causing the heat to build up either in a power transistor or a capacitor. Since it only occurs while the car is moving, some circuit that measures movement us putting a large load on the power wiring supplying you dme.
I am leaning to the electronic speedometer cable or pickup sensor or is there another sensor that determines motion as in a security system?
You say the dme is hot. Can you place fan near it to blow air over it to dissipitate the heat?
Your dme is good as steve wong tested it. You have a short that is manifested with movement.

[ischmitz]

Going back to the basics have you ever conclusivly determined if it is fuel, spark or both that is missing when the car shuts down? Get yourself a cheap in-line test light that plugs between the spark plug and the plug wire. It will tell you right away if the computer sees all sensors and issues a spark. Leave it in there and check it once the engine shuts down while an assistant cranks.

Then on to the tests others suggested once it shuts down: Measure fuel pressure (or the lack of) and fuel pulse (or the lack of) when it happens. 15 minutes seems like a nice window of opportunity to do some serious troubleshooting.

Ingo

[john walker's workshop]

did you check the cat yet?

[Dave Kost]

How can the cat cause this problem?

[wnsgc]

Sorry guys, I have not logged into the forum lately. As a recent update, while doing some testing, we by-passed the DME, just to see what would happen. Unfortunately this burned up the engine wiring harness. Thus I located a new harness, went thru it to ensure it was in good shape and then just installed/replaced it.

Oh what fun I'm having...

With all that said, I have not checked the Cat, but can you tell me why I should and what should I be checking in the Cat? When the car dies (during that 15 minute period), I do have spark, as I've connected a light between the plugs and the wire, and it does light up. It does appear something gets so hot, it tells the DME to shut down the fuel system. The fuel pump is working at that point, and the car has fuel. We've check the two rubber fuel lines before and after the pump and they're fine, thus it's something after that point.

The comment about the speedo cable and the pick-up sensor, can you tell me more about that? About two years ago, I had my speedo rebuilt by North Hollywood Speedo, due to a trip & odometer gear failure.

As usual, thanks and keep them coming.