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.

[DJsRepS]

Yea Im about a year into it myself. What I dont get is why MPS that d/n match my setup via #'s and has a massive vac leak works soo much better than the OEM one that tests fine both vac and electrical?

And another thing that I dont get is how running lean (via plug burn) can make such an erratic miss in all cyl sounding like an major ign failure.

Ive went to votek auto mech in hi school in the days of occilascopes, worked in garages, rebuilt many motors from scratch, rebuilt alot of manual trans and even an automatic in a 1ton Dodge van with all used parts from 2 free bad spares then packed it to the hilt even on top of the roof to move back to Fla. On the way a wristpin went out with a hurricane following me and I fixed it behind a truck stop with a used rod and piston. Pulled the head used the same rings and did the whold repair for under $50. It got me to fla and ran a couple years after untill I sold it with a bad freeze plug between the trans and motor. I would have fixed that too but I did not need it anymore.

Any way I consider myself well inclined to fix about any motor or at least find the trouble. And I would have bet $$ I found and fixed the trouble at least 5 times. I still dont have alot of $$ to be a parts changer or I would put in a 911 motor and 4 speed trany. I love my little 1.7 liter 80hp if that FI motor and gas millage and great handleing its good enough for me. I just wish I could unlock the mysteyes secrets of tweeking the MPS on a budget. I have read this link at least 6 http://members.rennlist.com/pbanders/manif...sure_sensor.htm It has been the best help so far. I would like to hear of others experiance with the MPS.