Bad starting & Sensor replacement?

[wayner007]

Giving up on the £450 944 so she's into my mechanics Tuesday for him to diagnose the starting issues.
If you haven't been following the restoration thread here's a quick summary>
Paid £450 for her 1985 square dash 2.5n/a she had been sat for around five years with various states of restoration, got her to do this years Scallyrally Millie Miglia in June.
So far replaced>
Spark plugs
Coil
Ht leads
Oil Filter
Fuel filter
Air filter
Fuel Rail
Battery
DME relay
New seats
Brakes overhauled
New Spax front springs
Alloys
Brake lines throughout(ongoing)
Braided hoses.

Basically she doesn't like to start from the key no end of turning over then she fires sometimes other times she runs the battery down.
Car will start on a tow start within a few feet. Will run on idle fine after adjusting the idle valve. Sometimes when she has been running she'll start straight after easy on the key other times she won't.
Done a flow test passed
Stripped the afm down and tested and done the later mod to add the bridging wire all passed.
Got spark.
Got voltage to the injectors.
DME test all passed.
Checked for vacuum leaks replaced hoses and jubilee clips.

Now the only things I can think of are crank sensor or temp sensor any ideas?
When cranking the rev counter bounces but sometimes doesn't which leads me too the crank sensor.
When she runs she runs fine for a car thats been sat for so long, did have a wavering idle but thats fine now.
Only place I can find the Crank sensor is Ebay USA is there anyone else?

 

[chrisg]

Hiya

I've got a similar issue with my '88 turbo - crank sensors are available from Burt at Berlyn Services or www.partsforporsches.com

I've just ordered one for ~ £100,

Chris

 

[sulzeruk]

I have some good used second hand ones here if you want, £20 each plus post, came from a fine running car, 1983 Lux Auto!
Alasdair

 

[peanut]

if there was a problem with the crank sensor it wouldn't fire at all. The ECU wouldn't pulse the injectors or trigger the DME/fuel pump etc.you also wouldn't get a spark.
Remember the engine must crank at a minimum of 200rpm in order to start .

When it doesn't start what do the plugs look like ? if you have a spark and everything is working the plugs should be wet. After running it up to temperature are the plugs really sooty ? wet ? or light brown ?

This sounds to me like a really simple problem. It wouldn't start and run so well if anything was broken or the settings badly out .

my guess is its lack of fuel when cold (possible temperature sensor is faulty.) or poor spark

Does the early 944 have a cold start injector ? if not how does the engine get a rich mixture when cold ? Have you tried removing the air filter and squirting easy start into the inlet when starting ? which would indicate a weak mix

I know that you have 12v at the injectors but have you checked that they are receiving a pulsed voltage when cranking off the starter ? Noid lights are only a fiver on ebay.

last thing I can think of is the ignition switch. Try wiggling the key about when cranking or idleing see if there is any change.

oh and I don't see a new distributor cap and rotary so have you carefully filed each of the cap terminals and the edge of the rotary with a nail file to a nice clean sharp edge ? Its essential to get a nice stong spark at low cranking revs on a cold engine . The fact that it is starting on a tow suggests that this problem is partially alleviated by a faster turnover of the engine when starting ie more fuel and more sparks

 

[awattam]

Starting from a bump but not on the key could also mean that there isn't enough power to both run the starter and give sufficient spark. When you're bumping it the battery isn't having to turn the starter so there's more power for ignition. I'd have a good check of the earths.

 

[peanut]

ORIGINAL: awattam

Starting from a bump but not on the key could also mean that there isn't enough power to both run the starter and give sufficient spark. When you're bumping it the battery isn't having to turn the starter so there's more power for ignition. I'd have a good check of the earths.

very good point [] I had assumed that they had already been done earlier.

 

[wayner007]

Thanks for the replies a few things to works through there.
It's got a new dizzy cap and leads and the rotor was cleaned up too with leech cleaner.
She does start after some serious cranking and seems to want to fire after you've turned the key off if that makes sense? Get a bit of a splutter.
Cold start doesn't have any effect really. Has started on a key but like I said takes a long time but tow starts within metres.
Last time I took the plugs out after a long time cranking they were fine which surprised me expected the engine to be flooded but it wasn't, I was pressing the accelerator as well. Did wiggle the key and the key fob for the immobiliser to but didn't have much effect. Not sure about a cold start sensor other than the temp sensor on this model tbh. Cleaned up the two other sensors yesterday and checked the readings against the specs and they seemed just fine. At a loss really now so like I said she goes into the garage Tuesday for them to take a look. One thing I have thought of is the battery might not be man enough for her although I did say the model and engine size maybe shes not quite high enough amp rated although I do have a booster pack which has had zero effect on the starting.
Sometimes though I get faster cranking then other times its a lot slower so turn off and try again then its back to normal cranking speed any ideas?

 

[peanut]

interesting that you say it sometimes seem to catch or cough when you release the ignition key. You may still have a defective ignition switch. If you can obtain a replacement switch you could just remove the wires from yours and attach them temporarily to the new switch if you are careful not to short anything.Pretty much any comparable switch from any car will do providing it has similar connectors as you are not actually fixing it , just leaving it dangling on the wires.

 

[Dockrell]

A problem that I had on a Lada Niva (don't laugh they are a very good small 4 x 4) was that the ignition switch was made in two halves and joined by a sprung ring, so it was not a complete circle. When the gap in the ring was in line with the joint of the switch body funny things happened - complete electrical power loss, intermittent cut out, unable to start on the ignition key, etc. Wriggling the switch made it work for a time. When the split in the ring was not lined up with the joint in the switch everything worked OK.
Don't know if the 944 ignition switch is built the same way but it's worth checking

Mike
White 2.7 automatic

 

[wayner007]

Getting somewhere now a 12v shorting to the starter gets her going and stays running fine just turn and turns with a key.
Somewhere around the ignition switch and immobiliser seems to be faulty so the auto electrician is taking a look now.