James_944

Hi All

I have had a problem starting the 944. It is an 8 V NA.

It did not seem to want to start, and when it did I had to tickle the accelerator to keep it running. Then it backfires and cuts out.

I pulled the reference sensors and checked according the Clark's Garage.
Resistances are ok.

I pulled the temp sensor and now she starts. Problem is the revs go high real quickly so after about 2 or 3 seconds I cut the ignition. Plug the temp sensor back in and I am back to the original problem.

Starting with the temp sensor removed the start is effortless, sounds smooth and runs ok with no backfires, or so it seems, just revs way too high. I recorded the start on my phone so I can see the tach reading is just over 3000 rpm.

Checked for obvious vacuum leaks but all of the vac lines have been replaced and reclamped with new clamps.

Any ideas what this can be?

I guess I have a faulty temp sensor, or the wires going to it. Would removing the temp sensor cause it to rev?

Thanks in advance.
James

944hal

Can't say for sure, but I have a similar problem starting. Tomorrow I'll unplug the temp sensor and see what happens. I suspect a bad sensor, connector or wire in the harness. I let you know.

James_944

Cool that would be great.
The wiring that runs over the top of the head was heat damaged and brittle on mine. I have replaced all the cabling since then and this is the first start attempts since then, although I tried a month ago and needed a new coil etc.

I am getting closer.

James_944

Here is an update. But it is still not starting and running properly. I am on the verge of giving upon this car after spending an absolute fortune on it.

I have tested all of the following and followed the Clark's Garage instructions on the following pages:
TPS checks out ok by http://www.clarks-garage.com/shop-manual/fuel-06.htm

DME Temp sensor checks out ok by http://www.clarks-garage.com/shop-ma...9.htm#dme-temp

IACV opens and closes ok when 12 applied as per
AFM checks out ok by http://www.the944.com/afm.htm


I have removed all the new vac lines around the throttle, no change.

If anybody has any clue at all where to go next I would really appreciate it.

Thanks

James_944

New parts installed:
Fuel filter.
Fuel pump.
Fuel lines around above.
Fuel lines at from from hard line to fuel rail damper and regulator.
Ignition coil.
Spark plugs + properly gapped.
Rotor (not distributor as this looked fine).
Vacuum lines - All of them, Y pieces changes for T pieces.

Tested the following, all seem to check out ok:
TPS
AFM
IACV
DME Temp sensor
DME Relay - resoldered and tested ok.

Removed idle screw and cleaned in carb cleaner, cleaned throttle housing.

What am I missing?

944hal

I unplugged my DME temp sensor but it didn't make a difference starting the car. So, I removed the intake and replaces the temp sensor, and idle control valve, as long as I was in there. Intake still off, so it will be tomorrow before I know if anything changed. When I do a continuity test across the two terminals on the DME temp sensor, while installed, I have a closed circuit.

BTW...mine is a Turbo, so maybe some minor differences.

mel_t_vin

How old are the FPR and FPD? When you disconnect the vacuum lines, do you see/smell fuel at the nipples/lines?

James_944

The FPR and FPD are original to my knowledge.
I was suspecting the same......... maybe there is a fuel pressure problem.

I could not smell fuel at the nipples with the vac lines removed so I guess the diaphragms could be ok.

The best way forward for me (I think) is to get a fuel pressure gauge and check the rail pressure. Maybe a new dizzy cap too as I do not know how old that is, while I am at it the leads are probably original.

James_944

Thanks for checking.
I tested my DME temp sensor at the sensor and again a the DME plug to eliminate the wiring harness repairs I made. Same reading that was within spec for a cold engine.

It backfired yesterday into the intake (I believe) while trying to start. A puff of smoke was seem around the vac lines under the manifold. I am starting to think I am going to take the intake off and check everything over again. Hmmmmm.

I do not have time for it this week, but possibly the weekend.

marc abrams

James, beside going back to check for a vacuum leak, try blocking off the IACV, and check for stuck throttle plate. Remember, if the engine is revving, the extra air is coming from somewhere. When you disconnect the coolant sensor it going full rich so you have the correct fuel for the extra air. Here in the US we use smoke leak detector machines to look for leaks in the fuel evap system. This works also for vacuum leaks too. This machine is expensive so maybe you can bring your car somewhere to let them do it before you tear it apart.

James_944

Thanks Marc, good points.

The car is not drivable at the moment so I am working on it at home.
I am sure the IACV/ISV (whatever you prefer) is ok, but that is based on tests listening for some movement when applying voltage. Apparently you can take these off without removing the intake. I may do that and strip it down, clean it and check that O ring. It will (if I can get it off with intake in situ) allow me to check the other vac lines. I am not sure they are all 100% correct.
Is there a way to simplify the vac lines to get it running, then add them back in one at a time? I may look at that.
I understand the IACV/ISV is supposed to vibrate in continual operation with the ignition on. Is that correct on an 8V NA?


Thanks

marc abrams

I would not go by that James, thats why I recommend blocking it off.

Sure, there nothing to prevent it from running. You'll have no power brakes.

Yes, on the late cars its DME controlled, on the early cars the IAC works on a bimetallic spring principle. Like a carburetor with an electric choke working in reverse.

James_944

OK I have found an issue, well 2 in fact.............

IACV was vibrating a little when the ignition is on. Decided to take it out and while I was in there re-check those hoses. Routing of hoses and for obvious leaks.

Well I found the short hose that goes from the valve to the manifold had in fact come off of the manifold, the clamp (which was obviously not tight enough) was laying on the balance shaft housing.

Well that accounts for vast amounts of air being sucked in and the revving.

The valve itself does attempt to move when voltage is applied. But it does not snap back and forth like I have seen on Youtube etc. It is more of a lazy vibration to the open position, then it seems to jam when attempting to close.

Looks like I may need a new one, or judging by the price more like a second hand one.
I may strip this one down first and see if I can get it going at all.

Thanks for the help so far, I will update soon.

marc abrams

Glad you found it James. I don't know the year of you car, but www.rockauto.com (in the US) have new Bosch ones for the 87 to 91 cars for $155.00 plus shipping. Here's a 5% Discount Code: 37696151DC4F12. Rockauto is my go to source for parts I can wait a few days for. They have a UK site also: http://www.rockauto.co.uk/

James_944

Thanks Marc. My car is a 1986 NA with an auto transmission.

That is cool, discount code appreciated. I will take a look at the site.

James