Dead Carrera '84

naples911 · naples911's Garage

Cruising along at 60 mph, my '84 Carrera just lost power and shut down. After pulling to the side of the road and trying to re-start, the engine turns over fine, just doesn't want to catch. As if it's starving for fuel.

The following is new: Reference sensor, cylinder head temp sensor, coil, fuel filter, fuel pump, rotor and cap. And, I switched out the fuel pump relay on the spot, nothing!

So, I'm a bit perplexed. Today, after towing it home, I shot some starting fluid in the intake and it sounded like it wanted to start. So, i'm guessing that the fuel pump might not be delivering, however, tested that by jumping the relays and it makes noise.

What next? Is there another sensor i should be replacing? I haven't done the speed sensor yet as it felt a bit stuck when i tried, but would a bad speed sensor prevent the car from starting? My understanding is the reference sensor is for starting.

What should I be checking next? It's usually the dumbest things that work so feel free to take a shot!

Thanks.

Flat Six · Flat Six's Garage

You didn't mention DME relay; I'd start there . . .

Also check grounds (esp. battery neg., cluster @ intake mainfold, and trans ground strap).

Either compression, ignition, or fuel. You might get FP sound, but check fuel pressure, too.

BTW, speed and reference sensors are not just for starting -- they provide ongoing info to DME during operation.

Good luck; keep us posted.

KNS · 05-30-2012, 03:18 PM

It sounds like you have already covered the typical problem areas. Check all the wiring and ground connections - make sure clean and tight.

I don't have any other advice but it is starting to get old seeing all these Carrera dying/no start issues!

naples911 · naples911's Garage

Thanks guys, I agree about checking the fuel pressure. Can I get that gauge anywhere?? I've done the ground straps before, sanded them down etc and it made a huge difference in performance.

It's funny, the tow driver said that he picks up just as many new cars of varying species as he does old ones. Mostly sensor issues

Buckterrier · 05-30-2012, 07:50 PM

Quote:

Originally Posted by flat six

you didn't mention dme relay; i'd start there . . .

+1

tnchris · 05-30-2012, 08:07 PM

DME Relay. My 84 did the exact same thing on the way to work one day, died while cruising on the freeway. A new relay had me on the road again.

scottb · 05-30-2012, 08:09 PM

Quote:

Originally Posted by tnchris

DME Relay. My 84 did the exact same thing on the way to work one day, died while cruising on the freeway. A new relay had me on the road again.

Same here. I bought two...and keep one in my glove box.

kidrock · 05-30-2012, 09:27 PM

first thing I'd check is the DME relay.

FWIW, I once had a bad fuel pump that fooled me. When I used a jumper on the DME to "hear" the pump run, I could clearly hear it "run". But I still wasn't getting fuel. Really pissed me off, so I replaced the pump anyways. Been perfect ever since....

chococrazy · 05-30-2012, 09:35 PM

Carry a paperclip bent into the shape to jump the DME relay in addition to a spare. Just in case they both somehow fail...

cary · 05-30-2012, 10:50 PM

Did you make sure the fuel pump relay didn't fall out?

QldChef · QldChef's Garage

I had exactly the same problem as you last week. Tested the 3 sensors in the engine bay, the reference and CHT were fine but the speed sensor was toast. Swapped it out with the BMW part and the old girl fired right up. Some posts say the speed sensor won't cause a 'no start' but on my 84 it did.

naples911 · naples911's Garage

The DME relay is the one next to the ECU beneath the driver's seat, correct? I changed this out but referred to it as the fuel pump relay. After a little research, i guess the fuel pump relay is the red relay under the hood. Do those go bad and if so how would i know?

Scott, how did you check the sensors in the engine bay? Thanks, i'm suspicious of that speed sensor as it's the only sensor that hasn't gone yet.

Keep you posted, thanks for the replies!

patina · 05-31-2012, 07:01 AM

DME relay OR Flywheel position sensors.

KNS · 05-31-2012, 07:45 AM

One of the guys here had a similar problem, replaced all the usual suspects and then some - he and his mechanic were stumped. Turned out to be a faulty fuel injector.

QldChef · QldChef's Garage

Naples, The procedure is outlined in the Bentley guide with pictures if you have a copy (p280-11). If not you'll need a Multimeter to test them.

From memory the speed sensor is the middle of the 3 sensors on the left hand side in the engine bay. Remove the 'clip' from around the sensor and pull straight out. The sensor has 3 terminals, the bottom one is no.1, the middle no.2 and the top no.3. Use the Meter to test between terminals 1 & 2 (the bottom and middle), this should give you a reading of 960ohms +/- 96ohms. The reading between terminals 1&3 and 2&3 should be >100,000 ohms. I couldn't get a reading at all on the speed sensor but the reference sensor tested within range. I had a mate test on the control unit under drivers seat and confirm it was faulty and the reference sensor was ok.

I hope my description makes sense and doesn't sound like i'm dribbling you know what.

wnsgc · 06-01-2012, 11:50 AM

Check out my current thread. I'm still dead in the water:

http://forums.pelicanparts.com/porsche-911-technical-forum/638355-3-2-engine-stalling-stumped.html

During a recent test, where my mechanic and I by-passed the DME relay, we fried the engine wiring harness. This weekend, we'll be replacing it (for the 2nd time). Let me know what you find out, and good luck. As Kurt said, these mid 80's Carrera's are starting to suffer the same issues - what ever that may be...

intakexhaust · intakexhaust's Garage

Believer in the DME relay syndrome... spare in the glovebox. One thing I've noticed if the car isn't driven often, things start getting haywire. From the age, when you seasonal drive it, things shake rattle and roll and connections loosen or fail without notice. Seals need to be worked and kept pliable too. Before you drop dollars on sensors and guessing, check and clean grounds, pull relays, check terms and spray contact cleaner, same for fuses, etc.. Check the wires going into crimps, blades, terms. You might be surprised.

KNS · 06-01-2012, 04:34 PM

Guys, for the third time, he's changed the DME relay

Flat Six · Flat Six's Garage

Quote:

Originally Posted by naples911

The DME relay is the one next to the ECU beneath the driver's seat, correct? I changed this out but referred to it as the fuel pump relay. After a little research, i guess the fuel pump relay is the red relay under the hood. Do those go bad and if so how would i know?

Naples -- Here's a FP electrical diagram that may help:

Fuel pump pressure testing is described in much detail in Bentley, 240-5. Should be getting:

~36 psi engine off
~29 psi engine running
~33-39 psi engine running w/disconnected vacuum hose to FPR

Quote:

Originally Posted by naples911

Scott, how did you check the sensors in the engine bay? Thanks, i'm suspicious of that speed sensor as it's the only sensor that hasn't gone yet.

Keep you posted, thanks for the replies!

Am pretty sure speed sensor affects running condition, while reference sensor affects start/no-start condition. See:

Good luck; keep us posted.

Dale

Quicksilver · 06-01-2012, 05:28 PM

Test the fuel pressure at the test port on the right fuel rail. Watching it as you drive will clear up any questions about fuel delivery right up to the injectors.

Test systems instead of replacing them.

To test the DME put it in a known good working car. That will clear it up and avoid the (slight) chance of damaging a known good DME because of a bad component like a shorted IAC valve.