Hello all, this is my first post on the forums, but have been "soaking up" information from here for a bout a year! This is a long post and perhaps a complex problem or multiple problems that I desperately need advice and guidance with. I am going to provide all the info I possibly can but if I leave something out please let me know! I will describe my problem first and then give a detailed history and specs of the car.

The problem:

My car will just not run smoothly across the rev range. I constantly have to give the car throttle inputs just to keep it running. When it does try to idle it is around the 400-500 rpm range. I can also hear pops through the intake if I try to hold the throttle open at a set point (hold the car at a specific rpm). If I am constantly moving/revving the throttle the engine will respond, but in exaggerated revving/deceleration. It also is very low on power when I do attempt to get it out on roads in the neighborhood. It also appears to be running very lean as all 4 of my spark plug tips are white.

Car/Engine specs:

1970 Porsche 914 1.7. The car is still fuel injection. I have most, if not all, of the service/repair records for the car including the bill of sale from when the car was purchased new. The car has the original engine (W004-9961). The car had a rebuild in 1977 that consisted of the installation of a HP camshaft (no description), 96mm big bore kit, lifters, rods, coil, seals etc. In 1980 the car had another major service consisting of: lifters, rings, lapped valves, and camshaft. This camshaft had a Porsche part number that matches the stock part number. The previous owner didn't have anything else major done to the car since the 1980 service. So the best I can tell the engine has a stock crank, cam, heads, F.I., distributor, but does have a 96mm big bore kit installed. The last time the car was running reliably was 1988-1990.

My service history:

-Engine removal for clutch replacement and flywheel resurfacing.
-While the engine was out, I replaced all the seals I could without removing the heads.
-Replaced all vacuum hoses, fuel lines, and clamps
-New F.I. and ignition wire harnesses (Thanks Jeff, they are gorgeous!)
-4 new fuel injectors with seals
-new points, condenser, cap, rotor, wires, plugs (NGK BPR6ES), and timed @ 3500rpm
with some help I was able to hold the engine rpms enough to time it.
- distributor vacuum advance tested and seems to be working
-AAR, CHT(new), manifold air temp sensor, TPS all test good.
-The MPS will hold 10in,hg for 30 minutes before dropping to 9.5 in. primary and secondary resistances are 89 and 349 ohms
-The cylinder compression is 160,160,155,150
- valves set to .006 at TDC for each cylinder
**edit** fuel pressure trigger points cleaned and tested, fuel pressure at 28psi

The bad news is the engine runs as poorly now as it did before I started working on it. I am out of ideas and could use some advice. I have religiously searched for vacuum leaks and have brand new proper metric sized lines. I have even gone as far as to use small spring clamps on the vacuum lines. The only other items that I haven't done extensive testing on is the MPS and the computer. My MPS holds vacuum and sounds like the internals are moving when releasing vacuum, but I don't know of any other tests that I can do without specialized equipment. I haven't stumbled across any references regarding testing the computer as of yet, but I hear it is rare for them to go bad.

Thank you all who have taken time to read this post, and thank you ahead of time for any advice big or small to help me.

Again, if I have left out any info that you think would be pertinent, please let me know and I will be happy to add it.

Thanks again!

Adam

I read through and didn't see anything regarding Fuel pressure being checked and trigger points. IMHO that around 32 PSI is where you want to be (96mm big bore).

I was laying in bed last night thinking that I forgot to add the fuel pressure info! I have edited the first post. Right now my fuel pressure is at 28psi and I am getting a signal to all four injectors when the engine is cranking. I can try the system at 32psi this afternoon and post the results! Thanks.

A few thoughts at first glance...

Have you known this engine to run well previously? If so, has anything changed/been done to the engine before this started happening?
Was dwell angle set before timing?
Exhaust valves if stock should be gaped at .008
Check the shaft of the distributor for "play"
Check the throttle position sensor for wear on the contact tracks.

Update on fuel pressure. Upon retesting the system I was surprised to see that I was running high, 38 psi to be exact. So I reset the regulator back down to 32 psi and ran the car for about 5 mins. Didn't seem to make the slightest difference but at least it is back close to the proper spec. I believe I will keep the gauge on the car for a few days to make sure my regulator is holding properly.

Adam

@Bob

Bob thanks for the list...

The last person to drive the car back in 1990 said it ran well enough to do a daily commute of about 30 miles 4 times a week. After that it was driven once or twice a month up until it was parked in a garage about 5 years ago.

I have gone through the distributor several times and the shaft and bushings seem as tight as any I have seen. Dwell, gaps, timing all set to spec.

The TPS has been disassembled and cleaned. when installed and set, I can hear 19 audible clicks as I slowly sweep the throttle from idle to WOT. If there is something else I can check with this let me know.

As for valve specs, the Porsche manual has the specs for the 1.7 and 1.8 motors to be .006 for both intake and exhaust. the 2.0 motor is listed as .006 In and .008 Ex. My manual is an old photocopy of the original so if the specs have changed let me know!

Thanks again for the checklist!

Adam

Did you rehab the fuel tank/pump/filters etc?
Some old gunk could have gotten through and partially clogged your fresh injectors.

Those are correct.

Have you read through, and spent time meditating on, Brad Anders' D-jet Bible? http://members.rennlist.com/pbanders

It explains a whole lot about what goes on inside the D-jet system.

--DD

@ Bob and Dave

When I first got the car I drained the tank at the pump and installed a big clear inline filter before the pump. Filter still looks quite clean and a quick inspection of the tank when it was empty, looked very clean in my opinion.

I have printed and bound all of Brad Ander's and Jeff Bowlsby's reference material. Been using Brad's guide for verifieing part numbers and test procedures.

**UPDATE**

I spoke with the previous owner last night after not being able to find a part number on my MPS. The car has a remanufactured computer and MPS from a place called Python Injection. I did some checking and I don't think the company is in business anymore. He wasn't sure if the problems started before or after he put the computer and MPS on.

Here is the 800 dollar question: Would a mismatched computer/MPS combo cause the symptoms that I have been experiencing?

He also mentioned that he always had a gut feeling that something was not right with the distributor. So I guess I am going to pull that out again and go through it top to bottom one more time to make sure I have not overlooked something minor.

Any thoughts about getting these components tested, or am I out of luck since they are aftermarket reman.

Again thanks to all who have been asking questions...Even though I have done most everything people have suggested it never hurts to ask!

Thank you!

Adam

I would think a mismatched MPS/ECU would have some effect, though the popping through the intake and low power sound like timing issues. Maybe a bad advance/retard canister or advance plate is sticking.

** YET ANOTHER UPDATE**

Went back through to distributor and cleaned the trigger points and verified that I don't have any play in the shaft. I also put a vac gauge on the advance/retard module and it is working as it should. Reset all the dwell, points, timing with out any different results.

I put a vacuum gauge on the manifold and am getting 12-14 in of vacuum at idle depending on the engine rpms.

The next thing I tried was disconnecting the MPS vacuum line running to the manifold. I left the MPS plugged into the harness but plugged the line from the manifold. The car actually runs and idles now better that it ever has. I was actually able to drive it around the neighborhood for about 30 minutes.

I have retested MPS as best I can...both the primary and secondary coil resistance is right on spec...and the MPS will hold 15 inches of vacuum for 30 minutes.

I am hoping to test my MPS on a running car this coming weekend...

That is where I am now...feel free to give any thoughts about what I might be looking at next!

Thanks

Sounds stupid but.....I solved 70% of my D-jet issues with a new battery and good grounds. The ground post above the battery, when inspected, was a pile of old paint and rust in the shape of a bolt. The ground strap at the transaxle had a corrosion layer in between the body and strap. My issues had appeared and worsened during year 6-7 of a new Optima Red Top battery. Replaced battery, then alternator was bad. Replaced alternator. It's been running great with 2-4 days of weekly commuting over the last month.

Good luck

Oh yeah, I should mention that 8 months ago I had the fuel pump die, but it wasn't the fuel pump, it was the ECU. In the process of diagnosis I went through lots of the D-jet and other electrical connections.

The other 30% fix was replacing the TPS circuit board, which was deeply grooved. Unplugging the TPS allows the engine to run fine at normal throttle, and will diagnose issues related to it (if the issue resolves while it is unplugged, your TPS is a culprit!).


Oh yeah, one more thing, my battery tested bad at the auto parts store even though it had 13V across the terminals. I thank Cap'n Krusty for the advice "even a bad battery can read OK on your voltmeter"

THis is still an MPS problem - I recently had a very similar problem happen and it was my mechanic that figured out it was the mps, for no good reason other than we had checked everything, he disconnected the vac line and it ran great! In a normal good MPS this should not happen. it should default rich and stop running.

my MPS held vac too, and the leads tested correct. but it was not good inside. It was running SO lean that when we unplugged it it defaulted rich but not as much as it normally would.
YOu need to test a different MPS - 96 that is same as a standard 2.0, so you should be running a 043 mps. maybe someone near you could let you borrow one.

-now it might be that you just need to tune the MSP - mine was shot but yours could just be set wrong, so if the epoxy plug is removed you can read PB anders and learn how to tune it but you need a A/F meter so that yo uknow whats happening. I re-tuned mine and has run perfect since( this MSP episode was 2 months ago and was documented in a thread i posted on the subject. )

Good luck-

There is still a mismatched MPS/ECU combo...

Silly question........but are you going off 1.7 specs for your existing mps?


If so......that.d be mismatched for 96 barrels as you don.t have a 1.7.


Am I missing something. Also....you didnt say what HP cam means. Stock cam?

Ooooops sorry......missed the stock cam part.

Did you go with the green injectors with the displacement increase? Didn't see that mentioned, but it just sounds like it's running lean.

Good point.

Thanks for the replies...but it brings a question or two from me!

@Chris

When I pulled the engine I did replace both the battery cables and ground strap on the tranny. The connections are clean and tight and a new battery. I have a battery from another car that I can swap but it appears my current power is good.

As for the TPS the car runs a bit worse when unplugged, and I can hear 20 pulses/clicks when I slowly sweep the throttle. I am still going to rebuild it with a new board when i get the part as the orig. board does show a bit of wear.

As far as the displacement increase, that happened back in 1976. The car was driven regularly up until about 1991. So, as far as I know, the car was running fine with the 96mm kit and stock motor setup. I have been told that the stock system on these cars will handle a displacement increase provided no other mods are installed (cam). This is why I have been setting the car to stock 1.7 specs...including the new yellow injectors. I hope I have not been wasting time and effort! Hind sight is always 20/20!!

@Phil

As for the computer and MPS setup...Those are still up in the air. Neither the computer or the MPS have a Bosch part number so it is hard to verify them.

I have a friend who has a 1976 914 2.0 still running the stock fuel injection system. He has offered to let me try out my MPS on his car this weekend. Some folks have said his car will run on my MPS if it is good. Might not run perfect, but the system will still understand the MPS...if it is working properly. Perhaps I can get him to lend me his for an hour to try it!!

I appreciate all the help and suggestions and would love any more advice or links to topics about the 96mm kit and running different injectors/computer/MPS!!

For now I need a few days to rebuild the TPS and test out my MPS!

Adam