Jack in Malta

Hi

Further to many post to the list I have run the tests from the Bosch Fuel Injection book from Ben Watson and apart from control pressure being a little low and a dodgy check valve I thought I knew what the problem was.

Now today after changing a couple of injectors I ran the car with the fuel pressure gauge in place (but open as I didnt want to remove the gauge and T pieces to warm it up). Does this measure control pressure when the car is actually running or system pressure or maybe nothing useful? as this fluctuates from 25 to 90 lbs when the car is revved from 800rpm to 4500 rpm also the tickover varies now from 800-1200 and the pressure reading goes up and down wildly as the tickover increases and decreases without touching the throttle.

Car runs much better! if the vacuum line to the WUR is clamped off. I adjusted the WUR as desribed so the control pressure (engine not running) is correct and now with the gauge connected and open whilst running the pressure is 70lbs
System pressure 78lbs , flow rates to and from the tank are fine and match the ben Watson book.

Injectors have equal flow.

Basically what does this measure - anything useful or not relevant

Advice appreciated as always

Thanks <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

jpitman

Paul,
I did not watch my control to see if it moved with throttle, so cant comment on that fluctuation, except that it sounds wrong. The engine at idle uses maybe 10% of the delivered fuel, so there should be more than enough to keep pressure stable. 70psi control is absolutely wrong though - 40-50 is what you want/need. With the gauge fitted, tap open, you should see control pressure - tap shut gives system pressure. The control pressure modulates the deflection of the air plate (high control resists delflection) which controls mixture. If the control is fluctuating with no throttle applied, this will change plate deflection and affect revs. If I read you right, control goes up with throttle opening, and down again as it shuts? 78psi system is only a little over spec, but...?? I replaced all my vacuum leads (have 2 on the WUR). Have you checked for vac leaks in the WUR itself? See if it will hold vacuum. No leaks of fuel in WUR? What did your WUR produce before you got at it, and what did you do to it to get the correct control - what figure does it give now? Does it behave OK with the vacuum lead disconnected and plugged? Surging sounds like a false air problem.
keep the info coming, send a mail to Jay Kempf on 928@rennlist.org, he may have seen this before.
jp

Jack in Malta

Hi

Its seems strange. beofre i adjusted the WUR it went as low as 15lbs cold and 25 lbs hot but this is with the fuel pump relay shorted and the test done without the engine running.

Now when the engine is running the pressure is around 70 which is far too high so long as this measures real control pressure. Also when i try to measure system pressure with the engine running it seems to be at 65lbs.
Definately something is happening in here that I cannot find.

i have now fixed the tickover and its steady at 850. Its like the fuel would rather flow through the WUR circuit tahn to the return but when the car is off the return rate is correct.

if I hadnt fitted a replacement (refurbished and tested) Fuel Distirbutor head I would blame this but I still think something in there is sticking

Obviously the car is still running like a dog but interestingly open the trottle when the power is lost if you leave throttle half open it picks up for a couple of seconds, tears away and then loses power again within 2 seconds and this repeats until it cuts out. When you start its the same pattern again, car pulls for a few seconds, dies and then comes back to life again

HELP!!!!

Jack in Malta

Forgot to metion a couple of things.

The vacuum on the WUR holds up, and when the Ben Watson tests are carried out as per his specs without the engine running the Control pressure is 35-40 lbs.

These other odd readings only happen when the engine is running.

Dennis Wilson

Jackin,

Your control pressure shouldn't fluccuate that much. Have you checked your air metering plate to make sure it's centered and has free movement? Also check to make sure it is resting at the right heighth. Did you install the plunger in the fuel distributor upside down? The nipple goes down not up. BTDT. Does the plunger slide up and down freely with no resistance other than from control pressure?

If those are OK, the problem will probably be in one of the following:

1. Loose bimetal spring in the WUR.
2. Sticking relief valve.
3. Partially plugged decoupler orifices (8) in the fuel distributor.

Dennis

Jack in Malta

Hi In the last hour I had some developments.

i found another WUR in the Garage, pressure on the tests is 38 lbs with fuel pump relay shorted and engine not running. System pressure 78lbs.

When I start the engine, control pressure is 38Lbs, system pressure is 78 lbs. When I rev the car hard or soft, very little in the way of pressure changes (stationary) BUT when I try and drive the car, it pulls away well (left a few metres of rubber!) but then between 5 and 10 seconds later it loses power and on no throttle it dies , now the control pressure is increasing with the rpm again so if I try to rev it up before it vuts out the control pressure goes from 38 to 70+ lbs. If I stop the car and start it again so long as I dont drive it I can rev it up and control pressure stays at 38lbs.

This only happens after I have tried to drive the car on tickover its fine and revs very cleanly.

Could there be something floating around in the system somewhere that causes a blockage ?

Any ideas!?!?

Dennis Wilson

Guess that rules out the WUR as the problem. Was the relief valve replaced when you replaced the distributor?

Dennis

Jack in Malta

Dennis

Changing the WUR did make a small difference but the main problems is still there.

The fuel distributor is a fully refurbished one, thats was "checked and tested on a Bosch flow bench " before it was shipped to me, it looks new but... its keeping a steady 78lbs bit personally I think its the problem. Very hard to say for sure without shipping it back to them.

Should I strip down and check the flappy on this first?

When pressurrised the flap is very firm, equal fuel flow to all injectors, but I cannot ell when the car is driven.

Whats the difference between tickover and revving it up in the garage and driving the car because its the driving the car that shows the problem, without the extra load of driving everything checks out

I am really confused!

Dennis Wilson

Jackin,

Reving in a load you need extra fuel which you aren't getting due to the high control pressure. When you intitally move the air sensor plate there should be a lot of pressure. Repeating should result in less resistance.

Do you remember if the nipple on the plunger was up or down? If up, it could be blocking the flow of fuel from the control pressure chamber to the decoupling orifices.

Was the rebuilt distributor shipped with a new relief valve or did you use your old one? A sticking plunger, like occured to a lister on the email list, could also cause your problem.

Dennis

jpitman

Paul,
I tend to agree it sounds like a distributor problem, not WUR anymore. Maybe the air plate ? Did the new distributor come separate from the air measuring part, and you assembled the two, or all as one unit? Is all the external plumbing fitted to the right ports?
jp

Jack in Malta

Hi

The plunger is the right way round, the relief valve works OK, I have never removed the air flap but could this cause the control pressure to fluctuate.

To be honest its more like the plunger sticking although I cant image how it can stick because if I push the air flap even right down the plunger falls immediately.

When this problem starts the control pressure just keeps going up and down on its own!

Turn off the car and start it again and its fine until you actually drive the car

Whole thing is crazy esp as the "refurbished and tested Fuel Distributor was supposed to have been fully tested."

If i had a spare 928 I could solve it because I would swap the fuel distributor and see if the other car did the same but..... <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />

Dennis Wilson

Jackin,

Are the injectors Bosch C1000-13511 or 928 110 225 00? If the injectors you have open at a higher pressure they could cause the intermittant increase in system and control pressure.

Dennis

Jack in Malta

The number on the injectors is

0 437 502 012 with 014 in a small square after the 012

They have BOSCH above the number and made in Germany below it

I replaced a couple of these but the previous ones had the same number.

All have the same flow rate

jpitman

Paul,
That injector number is same as mine, so I Think they are right. Sounds like something is blocking once you ask it for power, and clearing when the pressure comes off, but I cant visualize how that would happen. You are sure ALL the return lines are flowing OK, all the way to the tank??

jp

Jack in Malta

Jp

I agree with you, I cant imagine when asking for more petrol something sticks or blocks esp as it goes away after the engine is off.

The return pipe is so clear when you blow through it thee is no resistance at all.

Also tried with the return pipe disconnected and another hose straight into a jerry can. No difference and not recommended.
its like there is actually something physical inside the fuel distributor that blocks something when the plunger lifts to a certain point but I cant see how

Got the new coil and plug leads today from Devek, obviously made no difference but they look good!!

Paul