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Great to know that docmirror, and I'm really glad. I appreciate the offer for the fuel pressure set, but I have already emails 928sRUS to purchase a set so will go ahead with that. I'll need one in the long run anyway since I plan to keep this car .
dr bob, thanks again for the additional info, I'll be looking back at this post while I continue to work on this project, but there is a lot to do still. I have done the FD rebuild 5 times total to finally able to start the car, but it looks like I will have to give it another try as it seems it is still far from it working correctly. I have been carefully to track of all the items I removed: shims, springs, washers, etc. I noticed the small O-ring on the FD Seal from the kit I purchased did not look like it fit well, but I installed it so not sure if that could be one of the cause of the leak. Will take it out again and re-check everything to ensure nothing is missing.
Since you are deep into it now at 5x and counting... Are you using any of the good Bosch CIS books to guide your work? The 928 WSM gives some good info, but the real nuts-and-bolts stuff can take more than the WSM offers. Mine are stuck in boxes in the attic, or I'd give you a few eaxample titles to look for. I know Doc Mirror would know the good ones, especially after his Big Mondial Adventure. Since mine were acquired (mid- to late 1980's era) I'm sure there are good online references that didn't exist then. IIRC, the Charles Probst book "Bosch Fuel Injection and Engine Management: How to Understand, Service and Modify" was pretty much the bible at that time. There are new and used editions available on Amazon starting at around $10.
We met the author at a Devek Days 928 event in the SFO area in 1999. He was still sharp but in seriously failing health at the time. I understand that he passed away a year or two after that visit.
I'll need the fuel pressure gauge set to start troubleshooting too, but this morning I thought I'd take out the FD again and re-check everything to see if any of the shims, washers, or sprints, O-rings are not in place. Just incase something similar to what had happened with AirtekHVAC.
Any idea how far the control plunger needs to travel to the bottom of the distributor? I have it stopped where the flat surface is flush with the washer, and the pin goes through the opening. would this contribute to the fuel being pumped in the block?
What about the pressure relief valve. It seems from the FD rebuild instruction online shows there are 3 washers(as highlighted in my attached image), but mine only has 2. Also the small O-ring looks to be a little loose.
I don't have a mental image of your question on the plunger. You'll find, IIRC, that the little bellcrank arm on the lever is what keeps the plunger from falling out. If yours is hung up on something above that, the metering unit thinks you have a lot of false air flowing past the pancake plate; same as "lots of fuel".
The little washers you mention are shims that are used to set the fuel pressure. You'll know what's supposed to be there when you hook up gauges and run the fuel pump. Pressure too low means not enough spring pressure, perhaps caused by a missing shim. The gauges will tell you.
I can't tell you about the o-ring really. Again, the gauges will tell you. With fuel passing around the piston, pressure will be quite high. As designed, fuel pressure is on the bottom of the piston only, with shim-adjusted spring pressure above defining the controlled fuel pressure.
If you are new to CIS systems I would take a gander at my thread,"What I wish I knew about CIS in the beginning".
Also, I have to respectfully disagree with a poster about going in and starting to move the A/F mixture screw. It is 'highly' sensitive and one tiny turn either way can move your stoichiometric ratio for leaner or richer by 2-3 readings. That's ALOT! e.g. if optimum is ~14.7 it could go up to 16 or down to 12.
CIS is a multi-ring circus to get everthing working. The finally must be operating correctly for all to work in harmony:
- Distributor / A/f Mixture
- WUR
- Air Bypass valve
- Temp Sensors
- Engine Timing
- Spark plugs, wires, caps, rotors
- Fuel injectors
Since it was working before you fiddled with the distributor, I would start there first. As others stated, YOU NEED gauges. You need a baseline before you just start turning dials. Otherwise you are just plain guessing.
I would also reach out Jadz..he is a master of the of OB and CIS systems and his website is a wealth of information.
checkmate1996, Thanks for your post. I'll slowly read and get up to speed on CIS, but it'll take some time. I have tried looking up your thread as suggested, but as a new member, I'm having challenges with the site and not yet able to find it, but if it's here, I will find it .
As an update for all, I spent the day yesterday purchasing and getting the fuel gauge setup and ended up able to get the fuel pressure reading only but not able to do anything else. Here is the status below, and I'm not sure if it's normal:
1. fuel pressure ready at start up and car running: 3-10 psi
2. after a few minutes, at idle only, psi started climbing slowly and around 5 minutes or so, I get a reading of 32-35 psi.
3. Turned off the engine, and the pressure seems to drop very slowly, after 10 minutes, it's at 15psi with engine off.
White smoke with small amount of oil mixed with fuel(I think) still dripping from the exhaust.
The question I have is it seems at around 32psi and at idle the fuel requirement is low so the plunger should lift and return fuel back to the tank but maybe it is not happening as I thought.
Any thoughts on the psi reading?
Thanks again for everyone's input and suggestions.
You failed to read the direction to take the plugs out and not crank the engine. Remove the plugs now. Do not crank the engine.
Section 25 of the workshop manuals gives the spec settings for the system.
System pressure should be between 5.2 and 5.8 Bar, If it's at or beyond those limits, the adjustment target is 5.3 to 5.5 Bar. This in the roughly 75 to 80 PSI range, so the readings you share are not close to the desired range. The settings are taken with engine not running, airflow zero and plunger not lifted at all. The fuel pump relay socket is jumpered 30 to 87 to cause the pump to run for testing.
Since you have a lot of fuel passing through even without adequate fuel pressure. Figure out why so much fuel is flowing through before you spend more time on the basic pressure adjustment. The WSM has basic fuel delivery numbers too, but it doesn't sound like low flow capacity is an issue yet. At zero airflow, there should be NO fuel flowing through the metering unit. Get that flow stopped, then the system pressure. Leave the warm-up regulator unplugged too, until you are ready to actually run the car.
Also -- the leakdown spec is minimum is 2.0 Bar after 10 mins, 1.7 after 20 mins, 1.6 after 30 minutes.
Also, I have to respectfully disagree with a poster about going in and starting to move the A/F mixture screw. It is 'highly' sensitive and one tiny turn either way can move your stoichiometric ratio for leaner or richer by 2-3 readings. That's ALOT! e.g. if optimum is ~14.7 it could go up to 16 or down to 12.
Good luck!
That was me. If he leaves it where it is, he's doing potential damage to the engine, and causing a fire hazard. Start so lean that the injectors aren't even firing at all. Work from lean toward rich. As it is now, the injectors are flooding the engine as soon as the starter is engaged, and as long as the engine is running. His oil is maybe 15% or more fuel diluted, because the engine hasn't warmed up enough to vaporize it off. It's much safer to work the A/F lean to rich. It takes time for the engine to work out a rich mixture, and no damage can be done if the engine is too lean at idle or low to modest RPM. Of course, a lean mixture at high power settings can damage the engine, but not where we are at this point. Once the engine will run smooth, I advised to get to a CO meter and set it by the book value.
But, I appreciate the rest of your post, and think you make some good points as well.
As an update for all, I spent the day yesterday purchasing and getting the fuel gauge setup and ended up able to get the fuel pressure reading only but not able to do anything else. Here is the status below, and I'm not sure if it's normal:
1. fuel pressure ready at start up and car running: 3-10 psi
2. after a few minutes, at idle only, psi started climbing slowly and around 5 minutes or so, I get a reading of 32-35 psi.
3. Turned off the engine, and the pressure seems to drop very slowly, after 10 minutes, it's at 15psi with engine off.
White smoke with small amount of oil mixed with fuel(I think) still dripping from the exhaust.
The question I have is it seems at around 32psi and at idle the fuel requirement is low so the plunger should lift and return fuel back to the tank but maybe it is not happening as I thought.
Any thoughts on the psi reading?
Thanks again for everyone's input and suggestions.
Yes, I suggest you go back and read directions. If not, you are going to wreck your bores, or start a fire, or both. The pressures are way off. Also, the system pressure is inverse what you might commonly think -- in that you are thinking a higher pressure means a richer mixture.
Take a look at this graph, forget the absolute value of the pressures, but look at the slope of graph vs the control pressure based on temp.
Note that when cold, as in first start up the pressure is low. Which equates to a rich mixture, counter to what you are thinking. As the temp of the resistive element in the WUR climbs, the control pressure increase(slope of graph) and thus the A/F mixture gets leaner.
Think of the control pressure as the anti-enrichment if you like, but this reading you have describes an ultra rich mixture you are seeing. Low pressure = very rich. High pressure = very lean.
You may have seen this video as its in many of the other threads, but if not, you'll find it helpful in understanding how all the component parts work in harmony.
I forgot to mention that you want to disable the aux air and the start valves. The WSM offers some basic testing for leak-by on the start valve. If fouled and stuck open, or actuated incorrectly, you'll be dumping raw fuel into the intake.
The test protocols are illustrated and described in WSM section 25. You really need to be following that for at least the testing. Fixes for things can come from lots of places like yewteaub, but start at the original settings and specs.
Going back to your post 18, it's likely you will need that third washer to apply more pressure to the spring in the regulator. Also, if an o-ring is not snug in the slot, I would replace that too. Then try the control pressure test and report your results. Step-by-step, and stop just trying to swag it.
You should have him order the pizza and beer that you like, and visit the car for a bit. Some of this stuff can actually be done faster than we can type the descriptions.
You should have him order the pizza and beer that you like, and visit the car for a bit. Some of this stuff can actually be done faster than we can type the descriptions.
Yeah, we might get to that point. I HATE going to Dallas, but it may save a car. We'll chat if he goes off the rails again.
01-20-2017, 04:57 PM
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