Hello all, apologies for opening up as a new member with an old query - but can't seem to find the right combination in previous posts to guide me in resolving my poor running.
I bought a 1.7 very recently - it was one of two demonstrators used by Porsche in the uk in the early 70s it's registered in the uk in 72. It has covered round 73000 miles and less than 500 in the last three years it seems. It has good history and well looked after it appears original paint clean and all original. The car starts ok - it has its original injection system. It had an mot ( road test once a year ) until November next year. It feels a bit flat but lively in fits and starts - 'missing 'as you accelerate that bit harder. I'm putting some of that down to not being driven any distance for a long time. The real pain is that once warm or even warmed up a little it will just die as you approach a junction. I'm a bit unfamiliar with left hand drive the strange handbrake action (getting the hang of that now!) and the dogleg gearbox - trying to keep the engine from during and cope with the other new techniques required has been a little entertaining ! I hope that with just driving and driving a bit harder the engine might run better as it gets used, but the cutting out needs sorting. I have read on the forum and in the manual the richness of the fuel can be an issue at idle, and the exhaust is quite dark and sooty - but all advice seems to be dont try and adjust it without the correct analyser. Is that my next port of call - the garage and an analyser .... The car does restart ok ish .... Each time it cuts out but you have to give it plenty of throttle. Any thoughts much appreciated and very pleased to have found such a lively forum ! Best wishes. Jonathan

With D-Jet there are number of potential suspects to round up and question. Best thing to do is bookmark this and read repeatedly: D-Jet Parts and Troubleshooting.

First guess based on symptoms you describe is you're running too rich.

And

So is it 'rich' - "sooty exhaust", or 'lean' - "must give it lots of throttle"?

If rich check the TS2, the sensor by cyl #3. If the fuel injection is functioning correctly, one should never need to 'give it lots of throttle' like a carburated car due to the constant fuel pressure.

Thank you both for your advice and welcome to the forum. Will let you know how I get on ....! Best wishes Jonathan

Could be a couple things.
Have you done any work at all on it?
Set timing?
Check or replace fuel filter, ?
Check TPS setting? It will cause a bucking on acceleration if contacts are warn as well.
Bad fuel?
Injectors?

Check yor grounds for the f.i. System. I had a similar issue recently, missing hesitation etc and those grounds were not tight.-they are located at the rear center engine, remove the air cleaner, you will attached to the case 3 spade type(male) connectors that the 3 ground wires for the injectors attach. Make sure they are really tight.

I would take a look at your distributor as well. A broken ground or just rust on the shaft can have significant negative effects.

Best of luck,
Konrad

Thank you for the ideas. The car has had plugs - points - valve adjustment - oil change - new distributor cap and points at a VW garage in August. The advice from the garage was that it needed decent 98 ron fuel and being driven ...... It has only covered around 500 miles in the last 3 year. <I have tried to drive it rather than dive in as yet but its not a good experience. The car starts well when cold - idles ok. It misses as you drive it hard but not all through the rev range, if the engine is not under load it revs freely under load it misses more - have got up to around 5k rpm with missing under load no more. The car restarts when it dies - as it does at every junction but only with throttle. If you spin it without throttle - no joy at all. the garage who replaced the points etc said that they would investigate the injection system........ Only found this out after I bought her Hey ho ..... Happy to sort her but need to get an idea of what is required. The parts for the D system seem hard to get now or am I mistaken ? Again thank you for your thoughts and time - Jonathan

Your engine should sound like and be as smooth as a sewing machine if everything is functioning correctly. Here is another simple and crucial test but you need a hand held vacuum pump like a MityVac. Your engine sounds rich, and on D-Jet cars a prime suspect is a failing diaphragm in the MPS (Manifold Pressure Sensor), that grenade looking thing with a vacuum hose and 4 wire electrical connection on the right side of the engine bay.

The critical test is to apply a vacuum to the MPS port (remove the rubber hose that connects to the air plenum. With the engine off, verify if the MPS holds a vacuum of 15 inHg, or if it leaks down. If it does not hold a vacuum that explains the rich condition, the rough idle and drivability issues you describe, and the MPS needs to be replaced or rebuilt.

All D-Jet parts are still available if you know where to look.

I'm new to the forum as well but have had and worked on my car over the past 40+ years. My experience always tells me to start simple and work toward the more complicated. My '72 sat for a couple years so I started with a fuel tank flush , seal and fresh fuel. Then, as others suggested, change fuel filter. Have injectors cleaned by someone who knows what they are doing. Check your injector and rail supply lines for leaks with engine running. Then move on to the fuel pressure regulator and the other more complicated issues that the other folks mentioned. As they point out it could be a number of things. Try the easy stuff first. Good luck!

When I bought my 72 1.7 with D-Jet about 4 years ago it barely ran. It seemed like it was running on 3 cylinders. After I bought it I drove a couple of blocks from the sellers house and pulled over and started checking for loose wires, hoses etc. One of the fuel injection wires ended up being loose to the injector. I pressed all the connections down tight. I started it up and the car was running normally. So, too bad the previous owner didn't take a few minutes to try to troubleshoot the potential issues. He probably would have gotten another $1000-2000 for the car. I got lucky but sometimes something as simple as a loose wire can make our cars run like crap.

Happy New Year to all - thank you again for your replies - MityVac ordered ! To test he MPS - in the meantime I will check through for the loose - dirty connections ...., will let you know how I get on, interesting to hear the car is supposed to sound like a smooth sewing machine .... Mine sounds like a a lumpy beetle

Keep in mind with a 40+ year old FI system there can be multiple issues causing, aggravating, or even cancelling out specific symptoms, particularly if it has not been well maintained. This can lead you to chasing your tail based on what you think is happening. Some things, however, are just "good to do" including changing vacuum hoses, having injectors serviced, getting basic tune up and valves adjusted (as you did previously), and cleaning/checking electrical connections like you're doing now. The more variables you can cross out the more likely you'll either resolve a single major issue or eliminate multiple minor ones. As Twonicks001 says, knock out the easy stuff first. Validating that your MPS is working as Jeff described is one of those things that is easy to check (once you get your MityVac), and based on your symptoms there is at least a decent chance it's the culprit.

Again, there are really good resources for reference on Jeff Bowlsby's site, the Anders site I referenced earlier, and others. Here's more about the MPS than you probably ever wanted to know: http://members.rennlist.com/pbanders/manif...sure_sensor.htm

And here's another site I wasn't aware of until just recently. https://oldtimer.tips/en/d-jetronic/72-troubleshooting. It's not specific to 914's, but the info is all good. He (nordfisch) just joined the forum here recently.

Good luck and Happy New Year

Hello all - result of vacuum test on the MPS - pumped to 15 inhg - dropped to 10 inhg within 30 seconds - 7.5 inhg by 1 minute - hovered around 5 inhg for a longer period before being at zero inhg by 2mins 45 seconds.
Conclusive enough to say - no good? I'm guessing yes .....
So if that is the case - a new / rebuilt MPS for a 1.7 is required ? Assuming words of wisdom from the board is yes - anyone have an idea of where I can locate one ? Seem to be a few leads In the states but not a lot in the uk or Europe. Any leads welcome

Morning Jonathan,

I had the identical problem on my 1973 1.7; thanks to others on this board I checked vacuum on my MPS and that was the problem for me too. I bought a rebuilt MPS from Brad Mayeur (914ltd.com). Not inexpensive but easy to install and my problems literally disappeared.

You can also buy an MPS rebuild kit to fix your own from Chris Foley at Tangerine:
http://www.tangerineracing.com/mpsdiaphragm.htm

Hope this helps!

JD

I've read some conflicting accounts of how long the MPS is supposed to hold the vacuum, but yours certainly has at least a minor leak that is not ideal and could be a source of at least part of your problems. I also had one that behaved similarly. Jeff Bowlsby would be better able to comment.

The repair kit from Tangerine is great. I've repaired two of them, and it's not too difficult. It may not be possible, but if you can get ahold of a "known good" MPS in your area (you want one with p/n 049) with which to test that would be ideal.

Again, with aging/failing FI components there could be several things going on.

I actually have a spare x049 that I would have been willing to loan you for testing purposes, but I just did the vacuum check on it now and it's essentially in the same boat as yours (in terms of holding vacuum). That made me remember that when I ran that on my 2056 in that condition it wasn't ideal but it didn't run particularly poorly, either. Which leads me to believe that your MPS's leaky diaphragm may not be the primary culprit. Again, not ideal in terms of holding a vacuum, but not enough to cause the engine to stall out at idle or run "sooty" (IMHO, but guys like Jeff would know more).

Your symptoms suggest you're running way too rich. The basic reasons I can think of that cause that are:

1. MPS with blown diaphragm or failed aneroid cells
2. Fuel pressure too high (either from maladjusted regulator or blocked return line)
3. Failed (or failing) CHT / CHT circuit
4. Failed or disconnected TS1 (although this would contribute but not be the sole cause of this issue)
5. Injectors sticking open
6. Cold start valve stuck open
7. Dirty / worn trigger point contacts

Other can probably think of one or two other potential causes. If you have a fuel pressure gauge you easily check (and potentially scratch off) #2. If you have an ohmmeter you can do the same for #3 and #4. #5 is best done by sending the injectors out for servicing and testing (a good, cost effective thing to do anyway). #6 may best be done by rerouting fuel lines temporarily. #7 involves removing the distributor and giving a good cleaning (which is a good idea as normal maintenance).

Many thanks for the info Joe and to Jeff for the info on how to check the MPS - will give an update after sourcing or rebuilding !

Best wishes

Jonathan

Sorry BeatNavy - your replies didn't show up on my iPad before I had replied. Thank you for the kind thought of the loan of the MPS. I guess at least getting a properly vaccumed MPS might eradicate one possible cause before I work through the other possibilities you highlight ........ Doh! Will let you know. Best wishes Jonathan

Sounds like a plan. Replace that leaky MPS and see what a fresh MPS will do. If any remaining issues, keep looking. D-Jet is a system and is only as good as its weakest component.

I'm not an expert on these matters but one concern I read was you had a VW Shop adjust the Valves. Careful, I believe there are different settings for the 914 valve settings then the type 4 VW engine. I'll let one of the more experienced guys fill in the details on this if I'm correct about it.

Thank you strukn - the valves were adjusted by the VW garage before I bought the car - so no real detail of what they did exactiy settings size. Hopefully if the MPS makes a difference I can move onto the next stage of trying to get s smooth engine ! - we wil see

I know this thread is a little old... but did you get your problem fixed? Was it the MPS?