924Board.org

bear924 · Posted: Sat Mar 10, 2012 2:21 pm Post subject: My Three Cylinder Porsche

Hello all,

After owning my 924 turbo for 12 years, I have recently found the time to start doing some track days with my car.

I began to suspect that my car wasn't quite right at a recent track day when I was only matching the track times with a NA 924 and nowhere near the times of the 944s. Initially I thought my ability may be driver for my poor times however this changed when I did a drag day.

Essentially my best quarter mile time was a tad under 17.9s compared to a factory time of 15.7s (Morgan). Reading suggested that your actual quarter mile time isn't a good indication of car performance as driver error at the start will produce bad time. It was suggested that quarter mile exit speed is a more reliable indicator. My quarter mile exit speed was also below reported values (can't find exact figures now) so this made me consider why my car was so slow. My quarter mile time was also quite consistent around the 17.9 mark so I think that is about what my car is doing.

I then decided to try to find out what was wrong with my car, I tested fuel control pressure and found it set a tad too low however I didn't notice any improvement after adjustment.

In between fault finding I attended another track day and blew one of my vacuum hoses (the elbow coming off the turbo to inlet pipe). Essentially the moment I went towards boost I my car would cut out. I found the problem at the track and used some heavy duty tape to allow me to complete a couple of laps before reblowing the pipe.

This experience encouraged me to 'finally' attack the vacuum system and test pieces that may lead to low power. I am now replacing all elbows and plan to do a vacuum test (using low pressure to positively pressurize vacuum system... awaiting pressure reducer to arrive) . Anyhow while I was going I decided to test my fuel injectors.

To test my injectors I ran all four into 2L softdrink bottles at the same time so that I could inspect spray and measure total flow. Low and behold I found on injector with significantly reduced flow:

Even though the photo suggest that the low flow injector provided about half the flow of the other three, the bottles have an uneven base that would hold significantly less volume per height than the rest of the bottle. I suspect the faulty injector is actually putting out about one third the amount of petrol as the other injectors. (Hence my car was essentially running on three cylinders)

I now plan to replace the injectors (tow of the other injectors were close to a direct spray) and hopefully this will significantly improve my car's performance. (Plus if I find a vacuum leak, that won't hurt.).

If anyone has any thoughts on other things I should check please feel free to suggest.

Thanks
Wayne

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

See if you can find a fuel injection cleaning service in your area that will work on CIS injectors. I use a place called Jaguar Injector Service in Florida, and I've had him flow match three sets of 931 injectors for me. I've also had him clean cold start valves. I would strongly recommend this even for new injectors on a competition car because even new there can be a surprising amount of variance between injectors. They are not precision devices, after all.
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erstwhile owner of just about every 924 variant ever made

bear924 · Posted: Sun Mar 11, 2012 1:26 pm Post subject:

Ideola,

Competition car might be stretching the truth a little however I will see if I can find somebody.

Researched the new injectors yesterday and found the following part codes which may be handy for someone in the future. I'm sure this information is already on the board somewhere however more the merrier.

Fuel Injector Bosche and Porsche part numbers:

Early 924 (up to '79 I think) - 047133551 (I believe bosch #)
Later 924 not turbo - 049133551

For the 924 Turbo

Porsche # - 93111022500
Bosche # - 0437502017

Googling suggest that the Porsche number is the more prevalent in spare parts lists etc.

Interestingly the 924 injectors appeared to be used in later model 911 turbo's, ending with the 964 turbo. I wonder how many other 931 part numbers are in a 964 turbo?

staticsan · Joined: 19 Jan 2009 Posts: 450 Location: Sydney, Australia

One tip that could help you find someone who knows the K-Jetronic CIS is to find a mechanic who specialises in older European cars. That's how I found my guy. Bosch's K-Jetronic was used in Audis, Volvos and a number of other marques as well as in Porsches. A lot of "fuel injection specialists" only know various newer electronic systems, not the older mechanical CIS. Even racing specialists are reluctant to look at the old CIS our 924s have.

Wade.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

The 931 injectors are about double the cost of the NA injectors. There are a handful of crossover parts from the various 911s (930, 964, and even 959!), but this doesn't really help availability or pricing

I would suggest sending the existing injectors in for service before trying to buy new.

The other distinct possibility is a fault in the fuel distributor. If the tiny slit for the #4 port is partially clogged, it will definitely affect fuel flow. This is another area where I would strongly suggest enlisting the help of an expert rebuilder. Most of the attempts I've seen to service the fuel distributor at home have required at least two attempts...
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erstwhile owner of just about every 924 variant ever made

homey · Joined: 31 Jan 2009 Posts: 31 Location: Lynchburg VA

Check out AutohausAZ

http://www.autohausaz.com/search/product.aspx?partnumber=0437502017&gclid=CI2i2pHt3q4CFUZN4AodiSNrXQ

I got very good results on a fuel accumulator from them
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1980 924 NA, M471
1972 914 1.7
1992 HD 1200 Sportster
2002 HD TC 88 Superglide
1994 Jeep Grand Cherokee, converted to 5 Speed
PT Cruiser ,
and 5 Jetskis

9xx · Joined: 18 Jun 2006 Posts: 627 Location: Jarvenpaa, Finland

You can do some basic injector cleaning by yourself too.

1. Spray some carburetor cleaning solution to the open end of the injector and let it soak for some time
2. Install some thin line around the needle in the other end and pull the line in order to open the injector (thin fishing line is good, for example)
3. While pulling the needle, blow some air into the other end. If you don't have air compressor you can buy some canned pressurized air. It will be strong enough.

Extra pair of hands will help of course. Repeat this method few times. It will clean them up nicely but of course sending the injectors to a specialist will be even better solution.
_________________
Mikko

All gone: 931 '82 Alpine White, original option "220" G31 with LSD + 3 x 944

Paul · Posted: Mon Mar 12, 2012 10:35 am Post subject:

Swap the suspect injector with one of the working ones and retest to rule out the dizzy and lines.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

bear924 · Posted: Mon Mar 12, 2012 5:18 pm Post subject:

Hello all,

Great set of replies everyone, I was of the understanding that the injectors were non servicable so it's good to know differently. I've already ordered new injectors however I will keep my old injectors and see if I can find a service agent.

The Autohaus price is certainly good, I ended up paying $69USD per injector. I did find suppliers in the US who were had a similar price to Autohaus however they didn't do direct postage outside the USA. Autohaus appears to do this so drop ball by me. I will check out Autohaus for future parts purchases though.

After writing my last post I 'clicked' that perhaps the fuel distributor was faulty so I moved the injectors around. Essentially the bad injector stayed bad however this time one of the other injectors also put out less fuel. I moved them again and both stayed bad so I'm not 100% sure what's going on there. Once I have new injectors I will test again, to confirm I get equal flow. If I can source an CIS/ Injector specialist I'll also send the new injectors there for a check over before install. Does anyone in Australia have any CIS/ Injector specialist recommendations?

I'm enjoying everyone's injector thoughts, thanks.

bear924 · Posted: Mon Mar 12, 2012 5:18 pm Post subject:

Hello all,

Great set of replies everyone, I was of the understanding that the injectors were non servicable so it's good to know differently. I've already ordered new injectors however I will keep my old injectors and see if I can find a service agent.

The Autohaus price is certainly good, I ended up paying $69USD per injector. I did find suppliers in the US who were had a similar price to Autohaus however they didn't do direct postage outside the USA. Autohaus appears to do this so drop ball by me. I will check out Autohaus for future parts purchases though.

After writing my last post I 'clicked' that perhaps the fuel distributor was faulty so I moved the injectors around. Essentially the bad injector stayed bad however this time one of the other injectors also put out less fuel. I moved them again and both stayed bad so I'm not 100% sure what's going on there. Once I have new injectors I will test again, to confirm I get equal flow. If I can source an CIS/ Injector specialist I'll also send the new injectors there for a check over before install. Does anyone in Australia have any CIS/ Injector specialist recommendations?

I'm enjoying everyone's injector thoughts, thanks.

bear924 · Posted: Mon Mar 12, 2012 5:18 pm Post subject:

Double post.

staticsan · Joined: 19 Jan 2009 Posts: 450 Location: Sydney, Australia

bear924 · Posted: Tue Mar 13, 2012 6:05 pm Post subject:

Hello Wade,

Everything is 'quite a distance' from south west Queensland so the location doesn't matter too much. I'll see if he's happy to post etc.

Thanks for the link,
Regards
Wayne

musicalannette · Joined: 21 Feb 2012 Posts: 413 Location: UK

i'm just looking at the colour of your fuel in the bottles and unless it's the photo it looks a very funny colour, it should be clear not all brownish, are you sure the fuel system is clean and the filter/fuel system doesn't need cleaning aswell?
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I KNEW white wall tyres were invented by Americans .....just not at Boeing.... to be fitted on the 737.....