The MPS puzzle?, Lean mid range Options

[DJsRepS]

Ive delt with a bitchen miss thats driven me crazy for way too long. (about a year after a dropped valve repair) Ive read many posts and followed many suggestions and found many small fixes (some of I woudl have bet fixed it). Ive rebuilt the FI harness, soldered the relay board, ohmed every part and Tstat sensor. Cleaned and tested TPS and Triger Pts. Intake vac at 20" at idle. All new Ign OEM wires plugs etc.. No points (eletronic) all in distributer. Idles good reves good but crusing speed bucks. (the TPS tracks I bent arms slightly to start a new track then ohmed all). And the intake temp sensor is unplugged (runs way bad with it) MPS checks great both Vac and ohms. Sealed settings never touched.

Symptoms now idles good reves good but hold the throdle steady almost anywhere off idle and it sounds like massive ign failure.

I just pulled the plugs to check them and they look snow white. I turned the fuel pressuer up did not seem to help. I experimented on the MPS and made up a test I unplugged the hose from the MPS and stuck a vac gauge on it reading the intake, then used my new hand vacuum on the MPS.

Here is what I learned. (following all related to MPS controled by the hand Vacuum) If holding vacuum 15" w/n start right and starts fine at 0 vacuum as in normal cranking conditions. At 0 on the MPS barely idles, At 15" on MPS idles great. But at 20" on MPS idles bad (20" is my intake vacuum at Idle) Well then I went for crusing mid range rpm held the throdle missed like mad slowly pumped up the vacuum on the MPS from 0 and could tune out the miss totaly by adjusting vacuum to the MPS.

Helped eliminate my ign problem I thought I had. Running so lean and 90%RH in the air sounded like an ign breaking down. Problem alot less noticeable during dryer weather.

Seeing how I could tune out my miss using vacuume on the MPS I decided to open er up. My 72 has been stored longer than it was ever used. First thing I noticed was grease. Oil migrated and solidified in the control. I unsoldered the coil and cleaned it out. I removed the check valve like disk form the vacuum port and cleaned the grease from it. Mine had a smaller check plate and spring built into the disk and it was stuck! (first problem I found) I did not touch the sealed adjustments or the mystical sealed disk where all the adjustments rest as it vacuum test perfect. The next minor problem I found was the core stop arms had pad like things at the tips one missing and one falling off. I glued hard drive jumpers on the ends that touch the ever moving core. Reassembled and vac test perfect and tried it out exact same results no better and luckly no worse.

I am going to remove the glued on pads and try it on the car again, as they wrap all the way around the arms and add about 5 to 7 thousandths of an inch to the arms width. Im gona go with no pads and light touch on the shaft core with a touch of lube.

And as if to add to my confusion I tried an MPS in the car that has a terrible vacuum leak (wont hold for 10sec ) and is the wrong number all together for my system and my car runs great compaired to the OEM MPS. WHY??

Im leaving the bad MPS on for now. I would love to get this thing working right. Without spending alot on parts that dont cure my woes.

Should the MPS be sent off to a pro to be tested and set to specs on the bench or adjusted in the car with an exaust analyzer?

Pls HELP, advise me of any experinces (Good or Bad) any have you have had with the real brain to the Djet EFI system the Manifold Pressure Sensor the MPS.

[r_towle]

The settings are on panders site for each specific CHT sensor.

It can get stuck in a wide variety of positions...not uncommon.

I would suggest that the wrong MPS that you have may be an early type4 VW mps...this version had no diaphram.

It was the first version of the MPS that was manually adjusted, but I believe it would never hold a vacuum...not sure, but without a diaphram it would have a hard time.

It was adjusted by a longer allen head screw...it had a wide range of adjustments...

So, have you taken the original mps apart and fixed it?
Does it hold a vacuum?
If so, and if you have the correct meter...you can set it yourself.

Get it setup for your car. the 1.7 runs rich..its ok.

I would suggest also that you have a vacuum leak somewhere else.
Dissconect the Aux Air valve and plug the end that goes to the throttle body...seal off the plenum, make sure you are not getting a different leak.

I have replaced all the hoses...each of the old hoses leaks a little bit, but it adds up.

I have a few friends that have clamped every hose to ensure no leaks.

Look at all the rubber boots at the plenum and the intake runner boots, they could all be leaking a bit.

To test, wrap electrical tape around them...do a good job and you will stop a leak...

You should not have 20 hg of vacuum at idle..
I would search there...
If you can make the car run fine while applying 15hg of vacuum to the mps, that is what you need to have at that hose, not 20....search there first...find the leaks...

you may feel like you already did, but you may have missed something...

Here is what I did.
I disconnected every line to the plenum except the MPS and the intake runners.
None are needed to idle, once you get the car warm.
Even take off the cold start injector...it could leak through the body...
The intake runners could leak at the rubber connection to the plenum and at the intake gasket at the head.

The FI injectors have two seals...replace them..they cause a vacuum leak.

Go back and re-adjust your valves, pay close attention to detail and for the purposes of this test and only this test, make them looser than normal....this way you know they are closing...
Dont over compensate, just set them at .008 or .006 (I cant remember the setting)...but go one or two larger to make sure you get them to close...

The valves will also create a vacuum leak. odd but true.
If you have a burned exhaust valve, you will be pulling air through that valve while the car is running, thus creating a larger vacuum signal.

Get it down to just the intake and engine...then test the vacuum....
You may have a bad valve, a leaky head/cylinder connection....certainly rings...

Do a leak down test if you have the gear...

I would be searching for the 20hg vacuum issue first...

Or, if you are ok mentally running the engine till it dies in the current condition (nothing wrong with that) then adjust the MPS to your specific engine vacuum signal...

I.E. replace the 15hg setting with 20hg..
It is the transition that needs to be massaged...the WOT is no longer relying on the MPS...the idle and transition are all MPS driven...

You can tune your MPS to be correct with your car...
Geoff could as well..



Rich