MPS Options

[Bullet]

I also just discoverd that if i remove the Yellow hose (in the picture below) That the car runs alot better. runs ritch though. abd it will hold an RPM, instead of stumbiling. And it acts alot like it has a vaccum leak, Yet i cannot find one at all. I have checked the intake to head, Plenum to intake pipes, injectors, Throtle body housing, pinced off all the hoses, checked for any open ports on the Plenum. Is there another area that im missing? and i curently do not have my decel valve hooked up to anything. It just seems that it is running really lean. i was able to screw in the idle valve all the way and have the car still run. I dont belive that it is the MPS due to the fact that it holds vaccum and passes the Resistance checks.

(IMG:http://www.pelicanparts.com/914/technical_specs/Vacc_Hose_v3.JPG)

[RustyWa]

I was reading through some stuff on pbanders site and I read that my pcv breather hose should not go to the top of my air box but it should go to the air distrubtion box? and the i looked at this picture and he has it routed to the air box. I ran outside and tried this. but found out that the pcv house is to big for the hoses conections on the intake. so i used a ruber house to make it work. Car runs a beter now but i get a really anoying whistle when i do this. is this normal?

(IMG:http://www.914world.com/bbs2/uploads/post-2-1082882279.jpg)

'75-'76s do not have PCV valves. The PCV line runs from the oil filler connection to the air cleaner box, above the throttle plate.

What year is your car? I missed that.

[Bullet]

mine is a 75 2.0L. So you are saying that it goes to the aircleaner box? not below the Throttle Body?

[Bleyseng]

Air cleaner then if you have a 75 with all the smog stuff. I would plug all the hoses off and just have the MPS hooked up to trouble shoot this problem. This simplifies tracing a vacuum leak or whatever is going on.
Make sure the timing is correct! and that the dizzy hose is hooked up correctly.

Geoff

[RustyWa]

Air cleaner then if you have a 75 with all the smog stuff. I would plug all the hoses off and just have the MPS hooked up to trouble shoot this problem.

yup. (IMG:style_emoticons/default/agree.gif)

[RustyWa]

I need a reminder. The MPS has no effect on the IDLE. Is this a correct statement?

[Jeff Bonanno]

a quote from pbanders site (MPS page):

"The LVT, aneroid cells, and full-load diaphragm are visible in the diagram. At idle, the MPS chamber pressure is much lower (approximately 16 to 18 in. Hg) than atmospheric pressure. This pressure differential across the diaphragm causes it to be pressed hard against the part-load stop. The aneroid cells are evacuated during manufacture, and are normally compressed (flattened) due to atmospheric pressure. At the low pressure in the MPS chamber at idle, they expand. As a result, the armature is driven out of the core, reducing the inductive coupling between the coils. The contact trigger pulse is minimally coupled to the output coil, causing the ECU to send a short injection pulse. However, at idle, the throttle position sensor turns on the idle circuit in the ECU, which lengthens the pulse and enriches the mixture independently of the MPS response. "

not sure if the injector pulse length is completely decoupled from the MPS circuitry at idle but from the above, it sounds like the ecu takes over based on the TPS position

jbb

[pbanders]

The basic injection pulse width at idle is still determined by the "load" as measured by the MPS. Corrections are made to the pulse width for engine temperature, air temperature, and also for the idle condition. Idle condition is sensed by the ECU from the TPS contact. When it is "on" the position of the idle mixture knob on the ECU affects the mixture. The basic correction is set by the speed control circuit in the ECU. In early ECU's, there was no knob - the speed control circuit set the idle mixture condition. In later ECU's, the knob permitted the basic correction to be made richer or leaner by turning the knob. Most ECU's have a small "nick" in the plastic surround of the idle mixture control knob. That "nick" corresponds to the position of the knob where the mixture is set only by the speed control - the "factory" setting. I've found that most cars require a setting no more than +/- 3 "clicks" from this position to have the CO set correctly.

[Bullet]

So is that a yes or a No? does the MPS have an effect on the Idle mixture? I have Not been able to find a single source for a vaccum leak and i have had 3 others have a try at it also. Could this all be a result of my Camshaft. Since i have incressed valve lift, the valves are alowing for more fuel to enter the combustion chamber compared to normal. If i spray some vaporized fuel in to the throttle Body The Engine runs really smoth. but with out the additional Fuel it runs really rich. Can i adjust the MPS to run richer? I was reading on that MPS webpage and it says that I can en-richen for Partload and Fullload. Would partload be considered Idle as well?

[Bleyseng]

Only a leaky MPS has an effect on the idle as it screws up everything.
If you have changed the cam alot then you are on your own and should go to a dyno shop and adjust everything there using their equipment to set the A/F mix across the board.

Geoff

[Bullet]

I dont think that the cam would have much of an effect. when i called the guy he asked if i was using the Stock FI and if it was for street or track. so I should have gotten one that works. I hope anyway. But if i adjust the set screws mentioned in the MPS page. That will rich'n up the idle as well as through out load range right?

[Bleyseng]

There is no way to accurately set the A/F without a A/F meter of some sort. You can fudge tune the part load setting by ear but not the WOT setting. If you fuck up you can burn a hole in a piston by being too lean (Zeke did this with carbs).
You can remove the WOT stop screw and then adjust the inner and outer screws with a A/F meter. Then set the WOT settings with the A/F meter.

Well, what cam did this mechanic sell you? Varying much off the stock cam results in goofy idle, and other problems for the Djet as its a hard wired EFI.

Geoff

[Bullet]

I have access to a 5-gas machine at work that i was going to use to set the mixture. The camshaft is from Tacoma cam's it is the D-10 profile. They sell theese as a street car upgrade. I was refered to them for Porsche. Also co-worker with a 71 1.7L has the same Cam but his is carb'ed. But he said that he didnt have to do any tweeking at all.

[Bullet]

today a bummed a known good MPS that a co-worker had. and the Car runs great now. Still need to set the timming to 27 btc. But it purrs great. Nice to know that Porsche didnt build in a missfire (IMG:style_emoticons/default/laugh.gif)

[lmcchesney]

Glad to hear you isolated the problem to the MPS.
Different cams are said to have a significant effect on D-jet. The overlap and duration alter the vacuum signature.
What is the grind of the Tacoma's D-10 cam. at .005?
L. McC