964rh

Hi

Just got the car back from a 12k service and whilst in the garage the engine backfired and blew off all the connecting pipes to the inlet system. Mechanic reconnected and checked the car over but everything seemed fine. Car ran great when I took it home and yesterday when it went for a quick run.

This morning, started it up to go on a charity rally run and the same thing happened. Turn the key, couple of cranks and a pop/bang followed by oil smoke from the engine bay. Had a look in the engine bay and all of the inlet pipes held on by jubilee clips had popped off. Reconnected as well as I could and the car started and ran but seemed to be a bit low on power. In low gear it hestiated a bit before taking off.
Went on a bit of the run and noticed I wasn't getting the usual 4k rpm and 6k rpm tone changes on acceleraration. Hesitant now and again when in a low gear, not all of the time.

Any ideas what could cause this? Could my mech. have done something on the 12k service?

Thanks

Rob

Heirsh

i would double triple check all your ht leads. Check the dist cap and see if there are any carbone trails where they shouldnt be. Loose wires, etc. Could even be a spark plug wire on the wrong spot somewhere, but I doubt it would only present a problem on startup.

As for why you are down on power now perhaps you didnt get all those rubber pieces secured or maybe one has a real hole in it now giving you a constant vacuum leak. I would probably take it all off and make sure it all looks ok. Of course, you cant do this every time you start it, so its imperative you find the real problem, not just fix the results every time it happens.

Thats about all the help I can be. Good luck.

Red rooster

Rob,
That is one hell of a backfire in the inlet. Did he do the valve clearances ? I think they should be checked.
Leads , etc could give a misfire but it would be unusual to give inlet backfires.

Maybe take it back ?

Good luck

Geoff

964rh

Thanks

He did adjust the valve clearances Geoff, getting it back in the shop this week, I'll post what happens.

Rob

Porsche_Red

Does make you wonder if any tests were done prior to you taking the car. I had the same problem from a so called specialist - yes the car ticked over but as soon as you put it under load it didn't want to know. Did you have new distributor caps fitted - I had some that were not machined true when manufactured - put the old ones back and big improvement. I would check plug connections first and make sure they are going to the right distributors in the right order then check for air leaks or unattached pipes that got missed on reassembly.

Heirsh

Well its got to be firing that cylinder when the intake valve is still open right? And if it was the valve adjusted poorly it would do it for some time after it was cranked, not just once, right?

I'm trying to come up with a scenario that could be causing this, but I'm not doing very well. Can moisture in a cap cause a single arc to the wrong cylinder, but then not repeat because it vaporizes the moisture?

I'm very interested to know what the solution is when you find it. Please let us know.

964rh

Someone has suggested a broken dizzy belt, could this be a possibility?

Spoken to the mechanic and it's going in tomorrow, he initally thought it may have been down to the fact that the car had next to no petrol in it when I left it with him for the service, but the tank was near on full when it happend yesterday.
I asked about the ht leads and valve clearances and he said it should do it all of the time if they were the problem. He's going to have a look and I'll let you all know.

Rob

Heirsh

Yes Robh. that just hit me as a possibility as well. I was coming on to suggest it. Someone should have suggested this immediately. (/bonkself)

If its broken then 1 set of your ignition is firing 1 plug (or none if lucky) each firing. This could easily be the problem and from what I've read has led to some serious damage. (imagine a cylinder firing so far before top dead center that you get a nice hole in the piston to let the gasses escape)

As for the valve clearance it tightens up once its warm as the metals expands, so its possible for it to only happen for some time after you first crank it. I think it would be difficult to do this though, so I doubt this is what is going on.

tgage

I had something similar happen on a C2 I use to own with the symptoms being hesitation and low power. The distributor belt was broken. Unfortunately, I did not round-trip back to the garage fast enough. The CAT over-heated and burned up.

On my C4, I also had some hesitation problems after putting the engine back in which was related to air-leaks in the connections. Does not take much.

If this turns out to be the problem, there is a guy here in Atlanta that repairs them and also puts in new bearings. He is an air-craft mechanic and does this for sport.

Red rooster

Rob,
I would still be suspicious of a very tight valve clearance.It is a well known cause of cold start intake backfire .
This was just a suggestion as this was an obvious area that had been touched
and fitted the symptoms.
Maybe the distributor belt broke during the service ! Nothing is impossible !!!

All the best

Geoff

964rh

Thanks all

Dropped the car in to the mechanic today and mentioned the valve clearance and dizzy belt.

He's going to recheck the clearances and look at the dizzy belt, the hesitation is from a leak when I didn't put the pipes back on properly. Hopefully the valves will be the cause as this is one of the places touched as you said Geoff, on the service.

Will keep you informed

Rob

Rob

springer3

The car was in for service and they did not check the distributor belt? There is a question about the valve adjustment they performed? It was fine before they worked on it?

I think it is time to find a new shop.

964rh

Hi

So finally got the car back from the shop and the diagnosis was as follows :

Two weak coil packs, which caused the missing and rough running which (in my ingnorance) I've had since day one of ownership
Clogged fuel filter (presumably from when the car ran out of petrol in the shop)
Dodgy, new, spark plug which was causing the intake system to go skywards on startup.
Compression test reveals slightly more leaking than I was expecting, but it's not using any oil what so ever, and it runs perfectly

Got a fairly decent bill due to the diagnostic labour to find out what was making the car miss, after the spark plug issue was sorted.
On a short run on the way back from the shop, it pulls like a train and as smooth as a babies a*se.

Glad to have it back tho', been like a bear with a sore head on comedown since this issue raised its head, roll on Donnington on Friday and the ring in Sep.

Thanks for all your help

Rob