914-4 D-jetronic Driveability issue

[marconi502]

Hello everyone, I'm new to this forum and I hope someone can give me some suggestions.

I'm working on a Sterling Sebring kit car from the late 70's that has a 1972 porsche 914 engine in it. it is a code EA 1.7L 85 Hp engine complete with D jetronic injection. It has a 022 906 021B ECU which goes to a 1971 code W 1.7L it has no idle adjust knob

First I'll offer a little backround. This car has set in storage for about 15 years, it belongs to a friend, and I recently got it running. It was parked back then for a blown head gasket.

I changed the head gasket on the rh bank, and now compression is 120-125 PSI on all four cylinders.

All vacuum hoses are new, intake runner boots are new, air box does not have any cracks, holes or rust.

I have gone through the whole wiring harness, replaces a few connectors, cleaned everything up. I'll also mention I have an extensive automove electronics backround.

Intake gasket/heat isolators are also new.

Complete fresh tuneup

valves are set .006"/.006" cold - should they be .006/.008?

MPS holds vaccum. Cylinder head sensor is new. There are no vacuum leaks.

Idles well at around 1000 RPM. Runs fantastic when driven hard, has tons of power.

here is my drivability problem- if you are driving at moderate low speed such as around town in third gear, less than 40 MPH with your foot just barely on the gas, the car wants to buck and shake violently.. when you give it more gas, it smooths out but it makes driving around town a challange and the owner is not happy with it.

Runs best with about 32 PSI fuel pressure. if I take the pressure down it runs worse.

I did the injector test as mentioned in Rennlist with the four equal jars, and while cranking, it filled the four jars equally. The accelerator pump feature works on two cylinders which I believe is correct.

Engine idles at 19-20" of vaccum.

I have timing set at 28 degrees at 3500 - adding or subtracting timing does not fix the problem - it runs best with more timing.

Oil temp when fully warmed is 190 degrees F, engine also has an external oil cooled added, thermostat and air doors are set correctly and fully functional.

one thing I noticed with the distributor apart is that one of the pivots on the FI points is wore a lot more than the other and it will move around.

I'm going to order a fresh set from Pelican. I would think that this would effect all around driveability though.

I should also mention that I have a fully functional PCV system hooked up with everything but the blowback valve because I dont have one. Disabling the PCV makes no difference though.

I should also mention that since this is mounted in a Beetle chassis it is mounted backwards of how it would be in a 914 and as such, it has either Bus or VW 411 heat exchangers hooked to a single glasspack muffler. Do you think the lack of a whole 914 style exhast is causing my drivability problem?

Exhaust temps from all four pipes at 3000 rpm are around 385 degrees.

I dont know what else to do with this car. Any suggestions would be appreciated

[Dave at Pelican Parts]

Unplug the throttle switch. If the bucking improves, pull the cover off the switch and either clean it or bend the wiper arms so they run on a not-so-scraped-up section of the PCB inside.

Have you seen the tech articles at http://members.rennlist.com/pbanders ?

--DD

[marconi502]

Hi Dave,
thanks for the reply, throttle switch has been cleaned and adjusted per the rennlist article with no improvement.
Mark

[marconi502]

Since no one but dave has bothered to give me any hints or tips, Can you guys answer a simple question?
Should the vacuum advance be connected to full manifold vacuum or ported manifold vacuum at the throttle body?

I have made a considerable improvement in the driveability of the car and have almost eliminated the bucking by disconnecting the vacuum advance and running 31 degrees of timing a 3,000 rpm.

The distributor in this engine only has 1 port for advance and does not have the extra retard port as some do.

I would appreciate a reply.
Thanks
Mark

[John Rogers]

On the Porsche D-Jet setup, the vacuum line is used to retard the distributor, not advance it. You'll want to make sure the connection that has vac at idle, if there are two connections on the throttle body, is hooked to the connection closest to the distributor cap. It is a smog thing and the distributor relies only on mechanical advance to change the spark timing. Since your distributor only has the advance port then it does not have the correct vacuum pot it seems.

[Dave at Pelican Parts]

John, you're thinking of the 74 2.0 setup. The 73s had both vacuum advance and retard. The advance is hooked up to ported vacuum on the throttle body, while the retard line is hooked up to manifold vacuum, also on the throttle body.

The distributor should have two vacuum fittings on it; one pointing away from the distributor body (that's the advance) and one pointing back toward the distributor body (that's the retard). In 74 2.0 cars, the advance fitting is simply not plugged into anything. The retard fitting is still plugged in to the fitting on the "downstream" side of the throttle body.

I'm not sure what else the problem could be. Possibly something going on with the advance mechanism inside the distributor? Possibly a part-throttle lean condition?

--DD

[John Rogers]

Remember Dave, he said there was just an advance port so I am thinking it is the wrong distributor? Our 1974 had a 73 ignition system since it was made in Dec of 1973, also 1973 gauge/turn signal setup? I have been told my many folks this was Porsche's way to get rid of parts, figuring no one would notice.

Did the car get test driven without the throttle switch hooked up to see what part throttle was like? Since the car runs okay foot to the floor, it can be either the distributor and FI points or the throttle switch, probably both.

[Jay Laifman]

No help on the engine. But I have a Sebring too! Mine's powered by a Fiero GT V6 hooked up to a Super V built up tranny. My problem right now is that the top does not go up as smoothly as it used to and sticks close to the bottom going up. It too sat for at least 15 years.

Anyway, good luck on your car!

[MarkRobinson]

My car had slight bucking: was the throttle sticking due to a non-existent bushing at the gas pedal: replaced with bronze: went away. Cable is still a little sticky, but not enough to get me invovled laying face-down in my floorboard again.

[gwmac]

I had similar trouble with a bad throttle switch on a 74 Volvo.
Contact cleaner helped but not for long.
Good luck

[marconi502]

Thanks for all of the replies.
Currently I have 31 degrees timing in th engine @3,000 and the vacuum advance is disconnected. This has fixed most of the problem. There is a little bit of bucking in third gear on a flat road with little load on the engine. As soon as you give it a little more gas, the bucking goes away in 4th gear it hardly does it at all. Some of this may also be attributed to the fact I think the car has a VW bus transmission in it with 4:10 final drive. I doubt a Porsche would have ever had gears this tall or else it would not have any top speed.

I think it has the wrong vacuum advance on it it is a single port unit (maybe from a type 1 VW dizzy?).

If it had a two port advance on it, I would think it would tend to work more smoothly because it would work on a differential between the two vacuum sources.

I'm leaving it alone for now. the owner will need to decide if its worth the $150 for the two port advance to fix the remaining problem.

I tend to think that any of these engines will be a little touchy and never have the drivability that a new car will have, after all, they are air cooled, solid cammed, high compression (for air cooled), analog injection with points ignition! How more fussy can you get.

By the way, I changed the fuel injection trigger points and it made no difference.
The mechanical advance seems a little sloppy at idle, this may have something to do with the problem also, but it seems that it was all ignition related.

Thanks for the replies.
Mark

[MarkRobinson]

so, is the other vacuum nipple on the t-body plugged??

Mark

[marconi502]

The throttle body has both nipples on it, currently they are both plugged because I'm not running any vacuum to the advance diaphram at all.