My '79 Euro hybrid track car has been loosing power at 4,000. Under 4,000, it runs OK, but at 4,000 it starts popping and just won't rev any higher. When this happens the temperature climbs. I swapped out the ignition coil and TCZ spark box and found no improvement. I removed the distributor and inspected it and all looks good, timing is within spec and the springs are properly fitted to the advance mechanism.

I did some tweaking on the fuel system; added shims to the pressure relief and residual pressure valve and adjusted the air/fuel mixture and the problem seemed to be cured. It would rev cleanly up to 6,000 RPM.

I had some remaining time availabe at a local track event and went for some laps. At first it ran great and slowly (after about 10 minutes) it started loosing power at high RPMs until finally (after about 20 minutes) it wouldn't run over 3,000 RPM.

I removed the fuel distributor. The control plunger slides in and out smoothly so that dosen't seem to be the issue. I did notice something strange, when I removed the banjo fittings at the top of the fuel distributor fuel lines some little brown "caps" fell out. A few of the other fittings had the little brown caps remain inside. A few seemed to be missing the fittings altogether.

I see no mention of these caps in any documentation or PET. The probably are to divert the fuel to the outside of the fitting into the banjo fitting. My guess is if they came loose they could clog up fuel flow.

Does anyone know of a source of these caps?

Are they necessary?

 

I called John at SpecialTauto and he informed me that they are actually small fuel filters. They aren't necessary and the test is to remove them all and see if the car runs better.

He says that if removing them doesn't fix the problem, it is likely a control pressure problem with the WUR. I installed a rebuilt WUR less than a year ago so I'm hoping it isn't that.

 

You need to get a pressure gauge on the system, and see if your control is ok (~45psi hot), and system is holding at ~75psi when under load. This can be tricky to do if the problem only shows up on the track - you dont want a wet gauge in the cabin with you! Have you checked for system pressure and delivery rate (1360ml /30secs)? How long since fuel filter replaced? The little filters cab get clogged with crud - if you can get them out, they may look ok, but burn the crud off with a cigarette lighter and see the difference! There is a tiny one in the WUR inlet, which if clogged gives high control, lean mixture.
jp 83 Euro S AT 48k, BTDT.

 

JP

I have a gauge on the way. The fuel pumps, fuel filter, and WUR (rebuilt) are less than 1 year old. All fuel injectors were replaced shortly before the pumps and WUR. I doubt if there is much more than 10 hours TOTAL on the car since all of that work. There ain't much left to replace unless the rebuilt WUR is bad.

Pressure gauges will tell the story.

 

Can the screen in the WUR be removed for cleaning? How?

 

Do you have a rev-limiting distributor rotor?

 

The WUR screen is in an almost blind hole (maybe 2mm drilling through), and is almost impossible to get out intact. Damaged, no problem - fine wire hook should do it, or burn the crud out. I made progress with mine forcing carb cleaner back and forth through it, and compressed air. The gauge will tell you if this is the problem area. Best info on finding problems here is Watson - if high control pressure, open outlet of WUR - if pressure drops, problem is downstream further; if not, problem is behind opening (ie in WUR, or pipe from distributor...). I highly recommend finding a way to fit a gauge permanently into the control line, SAFELY, as it will tell you much about system health. If the guage reads ok, the spark distributor rotor is another good place to check, as the rev limiting unit was std here.
jp 83 Euro S AT 48k

 

No, standard solid rotor.

 

Update as of 9/25:

a. I tested the whole system and these are the results.

Note, the "system pressure" is regulated by the number of shims below the "residual pressure" needle valve spring. I tried zero, one and two shims. The shims are about .5 mm in thickness. I purchased a JC Whitney CIS test gauge system. It is quite satisfactory. The vacuum line was disconnected from the WUR (Warm Up Regulator). I didn't have a vacuum pump, so I didn't perform those tests.

a1. test 1, no shims on the system pressure regulator

Test Valve Open in WUR loop (from cold, ambient temp about 70F); testing the control pressure change every 20 seconds from engine start noting the RPM and control pressure. The main function of the WUR is to provide cold start enrichment.

Time(sec)/RPM/Control pressure - lbs/in^2
start/1400/28
20/1500/34 (2.3 bar)
40/1600/38 (2.6 bar)
60/1400/44 (3.0 bar)
80/1400/50 (3.4 bar)
100/1200/52 (3.5 bar)
120/1100/54 (3.7 bar)
140/1000/54 (3.7 bar)

Test Valve Closed in WUR loop 67 lbs.

The WUR appears to be working. The 54 lb/3.7 bar control pressure is a little high and valve closed pressure is low.

[system pressure (WUR loop valve closed) is the same with engine off and pump relay jumped]

2. Test 2, one shim on the system pressure regulator

Test Valve Open in WUR loop; 53 lbs/3.65 bar
Test Valve Closed: 78 lbs/5.4 bar

3. Test 3. two shims on the system pressure regulator

Test Valve Open in WUR loop; 54 lbs/3.7 bar
Test Valve Closed: 88 lbs/6.2 bar

4. Control pressure flow test

With the fuel pump relay jumpered measuring flow from the fuel distributor return line (to tank) I measured 22 fluid oz. / 651 cc in 30 sec. A book that I have says a typical spec might be 750 cc. I couldn't find this spec for Porsche anywhere, so I can't say if I'm too low here.

5. Fuel pump delivery: I have two fuel pumps, and the book says 1120 cc for one and 1360 cc for two fuel pumps in 30 sec. It delivered 54 oz / 1597 cc. So it is a pass on fuel delivery.

========================
So, the test to me says

- the WUR is OK
- with 1 shim I'm in a good position pressure-wise (what the book calls system pressure)


So, I'm just a little high on control pressure. Book specs are 2.8 to 3.2 bar for control pressure. The control pressure is a tad high, about .3 bar high (4.4 lb)

b. Test. We had a track day so I could test the car on the track. I found that it ran better, but after the engine was hot it started to cut out at 5,000 RPM (a bit better then the previous 4000 RPM cut-out). But, not good enough. Next, I'll try rebuilding the fuel distributor. I have pictures and instructions. It doesn't seem to be a real difficlult job, just replace $10 worth of O-rings and clean things up.

 

Try swapping out the coil?

 

Rich,

If your control pressure is on the high side of the scale, you want your system pressure to be on the high side also. Try adding one more shim. BTW are you adjusting the A/F mixture after each system pressure adjustment?

Dennis

 

Dennis, it ran worse with the additional shim. Yes, I adjusted the mixture after the changes. The failure mode is losing power as the engine gets hot (after about 5 track minutes in the AZ heat). The longer I drive, the worse it gets and the lower RPM the engine will turn. It seems to be running too lean at high RPM, the coolant temp climbs about 10F higher than normal. Yes, I've checked out the cooling system.

I'm done testing. Fuel distributor rebuild is the next task.

Thanks for all the suggestions. I'll be reporting the results.

 

Rich, I did similar unloaded pressure tests to yours when I was in trouble, and I found even when the control pressure seemed ok and stable at high 40s, after a pound around the block and soaking some heat, it went higher, and performance fell away (rice pudding skin, inability to remove, comes to mind). Control was now up to 60psi (system=75). I suggest your 1 shim regulator is good, but you need to get the control under 50. DO the Watson trace - crack open exit from WUR and see if control drops - if not, WUR is problem, etc. If the distributor rebuild is that easy, why does it cost so much (here in Oz, quoted at A$450)? Also I have been told that kjet shops will not touch a DIY worked on ditsributor. How about a copy of what you have on rebuilding one please? I occasionally (2/year) get a misfire that has been put down to a piece of dirt floating around inside there, but nothing worse. Have you found a neat way to permanently mount a pressure gauge somewhere?
jp 83 Euro S AT 48k

 

If the distributor rebuild is that easy, why does it cost so much?

That indeed is the $1M question. Part of the answer is few people know how to do it, another part is replacement parts are not known. Next part is keeping things clean. Mechanical parts issues require

If you go to this URL, and look at the photos and instructions it doesn't look so difficult. There really isn't much in there.

http://www.cfmstudios.com/928fueldistributor/

In my case, the WUR was just replaced and testing shows that it works properly (pressure decrease over time as the car warms up). The fuel distributor is over 25 years old. I'll bet some of the rubber O-ring seals in the fuel distributor has died.

 

Rich,

The toughest part is remembering which end of the piston goes in first or it was for me. If you have rebuilt a quadraJet carb, the fuel distributor will seem like a piece of cake. As alluded to, the correct size O rings can be tough. I ended up buying 8 cards of multiple sizes to play with. I would also keep the springs and valves/shims in their original positions. Clean the metal gasket real well and don't use too much adhesive on it or you will plug the decoupler holes. Actually I don't use any adhesive, just wheel bearing grease on both sides. So far no leaks.

Dennis