theiceman

Okay I have an update .. just got back from sitting by the sid of the road with this car ....
My friend came over and we put new plugs and a new Rotor in it as I happened to have some Carrera parts. We then went for a drive . Everything good , would ramp right up to full throttle no problem . headed to the high way and after about 15 seconds on the highway BANG the fuel cuts out. We managed to nurse it off the highway , could barely get it restarted and limped to a coffee shop Had to push it in . Waited half an hour int started and we made it about 1km at slow speed and it totally died and would not restart. I plugged in an old plug I threw in hios car and we had great spark but just would not start.

We waited another half an hoir , it started right up and we drove to a parking lot and as soon as we got there it started bucking again . We parked it and taxied it home .... So it is definitely the fuel , Lots of spartk but no gas.

When it started to act up on the highway i told hm to depress the cluth and the engine RPM began oscilating between 0 and 3,000 rpm , without any foot on the gas ... then it just died and we wrolled off the highway ..

I am thinking we need to check the CHT, sensor and the fuel pump , problem is the car really needs to get warmed up before it shows the problewm in order to check fuel pressure and we might be broken down by then

Any other thought s?

Ed Hughes

I don't see how that could be fuel pump with the fluctuation up to 3k with no throttle input?

TT Oversteer

Have you checked to see if the fuel filter is full of crap?

theiceman

yeah it has a new fuel filter, he says he has the old one at home he took out so i tld him last night when he gets home cut it open and have a look. ... Good point ed. I thought of that too lying in bed last night , but if the fuel leaned right out would it rev as it gasps for fuel ? not really sure just a thought. I guess we really need to get a fuel pressure tester to see if that is the case.

The question is what controls fuel input and the timing of those injectors then .
I have Russ's sensor checks so that would be a good start, but it definitely seams heat related. I guess I have to do some research to find out what some of these sensors do . I know the ref sensors contol spark and timing so we are good there. They also time injectors but if we have spark i am going to assume that is okay.
Lots to think about that is for sure.

theiceman

Oh a couple of points I forgot to add ...

The oxygen sensor was just dangling,, I could not figure out for the life of me where it plugged in, Since this is a 78SC ( no sensor) with a 3.2 transplant maybe this is correct? but I don't know how it runs with the O2 sensor discoennected. Although I have found this is entirely possible and just affects fuel milage.
I wanted to check the CHT sensor to make sure it was plauuged in .. couldn't even find the damn thing. Are there any connectors under the car ? I saw three connectors on the drivers side , Russ's diagram shows the speed and ref sensor . Not sure about the CHT

Thanks

Brads911sc

I had an old air cooled VW and it did this... It turns out I had installed one of those chrome bosch coils on it, installed in the standard place, oil leaked out and everytime it got hot and was placed under load, it left me sit on the side of the road... As soon as it cooled, it would be fine. It also behaved differently when not under load... Just because you have spark at idle doesnt mean the coil is good. Id swap this out just to rule it out...

theiceman

Brad I wanted to swap it out initially but it looks a lot different than the one on my SC Anyone know if they are functionally the same ..

Also when we were stuck at the side of the road i did the spark test .. this thing was cranking over like mad but would not fire and i was doing the spark test with the plug .. lots of spark but the engine would not fire ... that is what really confirmed fuel for me .. make sense or am i off down the garden path ?

Brads911sc

Makes sense to me. Definitely not sure what I was dealing with the is the same. It was a 72 beetle... but the symptom was the same... cutting out under load and leaving me sit. then running fine when cooled.
Perhaps someone who knows the 3.2 can chime in on whether the coils are the same on a 3.0 and 3.2.

theiceman

i have been doing some reading on the CHT sensor and I think I might know where it is now . I am going to ohm it out later when it gets back home .. the other thing I might do is take out the MAF ( if you guys call it that .. and check it over .. he said he overfilled it with oil last year , doubt this is the issue but ya never know..

whalebird

a couple of thing to check. Fuel: It is often overlooked, the fuel prefilter "sock" in the fuel tank: It will flow just enough to run for a few minutes untill fuel requirements want more. After a while of sitting, the system will accumalate enough fuel to run a little while longer etc. The fuel pump is much different on a CIS(SC) than on a Carrera(motronic), CIS operates at much higher pressure and has a different pump - something to consider on a transplanted 3.2.
What you are describing is a common failure mode for a DME. A known good DME and DME relay would be nice to confirm or eliminate.

theiceman

Thanks Whale gives me a few more things to check .. he is getting a DME relay ( even though his looked good ) not sure where we could borrow a DME . Is the sock easily accessable ? The car ran great all last year so i would imagine it is the right pump ,,

whalebird

Ignition wise, Firing a plug is much easier outside the combustion chamber than under compression, and even moreso under load. This is when ignition components start breaking down and can be a difficult diagnosis.

theiceman

whale do you know if the 3.2 coil is the same as my SC ? . The cap looks largely different.

whalebird

IIRC, the 911s all used the same coil - including turbos. At least the late 3.0/3.2. I suspect a comparison of part #s and their application would be prudent. The common Bosch blue coil is not a good replacement for the stock unit, but many chosse it because of it's reletive price. Stock coils are pricey.

theiceman

Some additional info ......
Tonight he took it out again and once it warmed up it died ,, so I went over with my meter and checked the cht sensor .. the car was some what warm and the reading was about 800 ohms . he started it and it ran,, after about 5 minutes he shut it down and I measured it again it was reading 160 ohms which is right on spec. I plugged it back in and he started it again .. while running i unplugged it and it began oscillating exactly as it had done on the highway .. plugged it back in and it settled right down .. did notice however it was the single wire unit which i have read previously as problematic. I suggested he upgrade as soon as possible.
While standing there i heard it stuter and something sounded like a rush of air . i took a closer look and right behind the connectors for the sensors there is a horizontal pipe. which atatches to a 1 inch or so piece of rubber pipe .. that clamps on to another pipe .. not sure what it is .. anyway i looked closely and saw what looked like a crack .. not sure if it was a surface crack or a split so pulled it to see and the whole piece tore right off ..
he is going to take the piece to work tomorrow and have his maintanance guys press a new piece of rubber on the pipe.
Not sure if it is the final fix but it is certainly progress.
still could not find where the o2 sensor plug into the wiring harness .. anyone got a pic ?

Thanks