Guy

Hello All,

For those that have been following my "79 5spd Save" many of this may seem repetitive but I post mainly in the hopes of paying forward all the help I have received over the years "lurking" around the site.

My 79 sat for 11 years. Over the past few months, I have removed and cleaned every fuel component and every line. I replaced:
Both fuel pumps
Soft hoses
Accumulator
Filter
Fuel Distributor (Rebuilt)
WUR (rebuilt)
Injectors (with seals)
Every VAC line
Rebuilt Air Meter/TB
Cleaned, tested cold start
Tested within spec, thermotime switch
Spark Plugs (BOSCH Copper)

This was not without logic, all of these components needed to be replaced.

Recently, I tuned the engine timing, idle and fuel pressures.

22 psi cold at 57 degrees
52 warm (with vac) 44 without

Rest pressure starts at 45 and stays there for about 15 minutes before dropping to 30 at the 20 minute mark. It is zero in about 30-35 minutes

System pressure is a steady 75.

A/F mixture adjusted to achieve maximum vacuum (approx. 20 at idle). Idles smooth now. Timing set to factory spec 31 degrees at 3000 rpm.

In short, car drives wonderfully. Has nice fast idle when cold, warms nicely and idles fairly smooth at 850. It starts instantly when cold.

So here is the rub, it has the VERY typical WARM start issue. It takes multiple cranks and is difficult to start when warm. Usually fires up for a second then dies and struggles to start. Don't get me wrong, at one time it was near IMPOSSIBLE to start but tuning and adjusting fuel pressures has made a difference

My rest pressure seems good, my pump has the integrated check valve. Accumulator is new. Cold start valve fully tested, no leaking. The thermotime was manually heated and it cuts power to the cold start valve right on spec. The injectors are new and not leaking down.

I have read hundreds of posts in this forum and others. Heck, I even ventured on the Mercedes and VW rabbit forums. The problem seems SO common as are the suggested solutions (accumulator, check valve etc). So I ask the group, with all these new parts and everything in spec........whats left?

Randy V

Sounds like you still have leaking injectors.

All symptoms point to that.

Guy

Thanks Randy, I am with you......except that I have removed each injector individually and inserted them in a baby food jar. I did the cold start injector today as well. None leak during the rest pressure test.

With my old injectors, that were leaking.....the warm start acted a lot like a typical flooding condition. Its now different, its sooooo close to catching as it cranks over.

checkmate1996

Rest pressure seems low to me. I recently had atleast 1bar of fuel pressure after 2 hours of sitting. With your spec, that would indicate that something is leaking. I would re-run your CIS gauge tests from the top. Verify you have solid pressure from the output of the WUR into the input of the FD. Those can be sneaky troublespots. Also verify your WUR gets within WARM spec of 2.8-3.2 and holds.

tailpipe

If it is showing all the signs of a ruptured accumulator use your gauges and make sure and prove that the new accumulator is actually doing its job. Just because it is new doesn't always mean it is working right....

Dennis Wilson

When you rebuilt the FD, did you check the o rings and seats on the relief valve? A leak at the valve can cause a loss of pressures due to fuel leaking into the retuen lines.

Dennis

jmartins

It's a nightmare... First time, one injector was leaking. Second time one injector not working - no fuel. Third time 2 injectors not working. Now I'm rebuilding it for the forth time... Let's see what is the next problem...

Guy

Thanks for all the good suggestions. I initially didn't suspect the FD relief valve as system pressure is dead within spec but I can always pull it and check the rings. I had the rebuild done for me so worth a shot.

The rest pressure is odd to say the least. It holds dead steady for a long time but when it starts to fall, it falls rapidly. I am tempted to add an external check valve of possible to the pump. Cheap test. I may try clamping the hose as well to the tank and see how that holds.

Guy

Added a used (80+) external check valve to the pump (which has the internal valve). It made a BIG difference in rest pressure. Now holds 40 psi for 15 minutes, 35 psi at 20 minutes, 35 psi at 30 minutes and around 20 psi at the 35 minute mark. Drops to zero after that.

Behaves the same way whether the valve is open (control circuit) or closed (system circuit) for the test.

I ordered a NEW external check valve to see if that helps out a bit although I doubt it.....I did one test with soft hose from pump to tank clamped shut and it reacted the same way.

I have not checked the FD relief valve yet nor have I tested how it starts warm as of yet. These readings seem to now be within SPEC of the WSM. Not sure how much better I should be striving for.

Thoughts?

Guy

FIXED!!

Did a few more rest or residual pressure tests after thoroughly warming car up. Got great results, in short it held well within specs (38psi after 30 minutes) and even had 5psi after nearly an hour.

Did a few "real world" tests starting the car after the fuel pressure subsided (40 minutes plus) Starts well warm, hot and cold now!!

Did it several times, it does not start on first crank when warm but it starts instantly on the second. Worlds better!!

What fixed it in the end? The VERY TYPICAL check valve. I have a NEW pump with internal check valve, it must be dirty or stuck. I added an external valve to fix this issue.

Thanks to everyone as always!!!

Jadz928

I was thinking that was to case. Porsche issued a TSB early on about adding an external CV.
This was allow to keep the working FP... no sense throwing out the baby with the bathwater.

I keep a couple extra externals on hand for this very reason.

Well done on getting her fixed!