How do I check the MPS on a 74 2.0 D-Jet properly?

Start with checking to see if it holds vacuum. That is all you can do at home...

It has been rebuild and it holds vacuum but the car runs way to rich!

your only 2 choices are to find someone with the wavetech that can check its settings or...

more realistically adjust it on the motor under load with a wide band oxygen sensor.

Geoff used to do this and it was cheap and well worth it!

or spend 300-400 and buy your own wide band to do it yourself.

An MPS adjusted on the motor is really the best way to go in my opinion because its "map" is really tailored to that actual motor and state of tune (whether it be a fresh or tired motor, etc.)

brant

Were do I get a wide bench O2sensor?
And how do I add it to the D-Jet?

Have you checked everything else first?

IE fuel pressure ect ect?

Mine did the same thing......fuel pressure was too high.

You probably already did this, but be sure the vacuum hose is connected properly and has no leaks (is pulling adequate vacuum).

The engine had been rebuilt by a shop twice in the last year because they cant get it right!

Everything has been checked, replaced or rebuilt. computer valves, sensors etc
They got paid back then and now threaten me with a lawyer if I bring the car back so they get it right.

They dont wanna loose any more money over there incompetence.

No the car is bad after 20 miles again!

Sorry...I quess what you are asking is to check the ATF ratio. A wide band 02 Sensor or a Wavtek.

There are many threads on the O2 sensor installation....but at the end of the day you will have to figure out or have someone tweek the MPS or rule out that it is not something else before you start tweeking it.

The problem is everything has been checked and rebuild,
so the cyl head temp is new and the other reason for a engine running way to rich,
(it misfires like a machine-gun), is the mps in my opinion,
correct me if I'm wrong,
and there certainly had the time after the car has been in there shop after the engine rebuiled for 13 month with the warranty claim
and now they refuse to fix it after they got paid back then.

Maybe somebody has also an advise for this situation.

I only have one vacuum connection at the Throttle body, so it makes it hard to sort the vacuum problem completely with the diagrams for a 74...

Simpler than that. I guess I was just suggesting to double check that the vacuum hose from the MPS connects to a port above below the butterfly in the throttle body and it's a good hose with no cracks/leaks.

If the MPS holds a vacuum for 15 seconds, and is plumbed to a good vacuum source, I wouldn't be too quick to suspect the MPS. It's pretty rare it would go out of adjustment enough to cause this kind of trouble. That is, unless the epoxy over the adjustment screw is gone and someone fiddled with it.

This sounds bad. Is this a ligit VW or Porrsche mechanic or Curly, Moe and Larry. Get they hell out of there and go get a lawyer after you find a reputable mech to straighten it out. Good luck. Your car shouldn't be that difficult to work on unless the mech doesn't know shit from apple butter. I think we can do more for you than your mech can.

EDIT: We need to some good pic's, too.

[quote name='Rand' date='Feb 17 2012, 03:41 PM' post='1627478']


Simpler than that. I guess I was just suggesting to double check that the vacuum hose from the MPS connects to a port above the butterfly in the throttle body and it's a good hose with no cracks/leaks.

Above or below??? Neither of mine (73 & 76) have a port that large above the TB butterfly. They both tie in on the intake manifold boddy next to the dist adv port.

Oh crap.... My bad. The less vacuum pulling on the MPS diaphragm, the richer it runs. So it needs to pull less vacuum with more throttle. BELOW butterfly.
Thanks for catching that.

1.) It needs to hold vacuum .. I pull 15" on the unit

2.) You should have 90 ohms (approximate) between the two outer electrical connections on the MPS Pins 7 & 15

3.) You should have 350 ohms (approximate) between the two inner electrical connections on the MPS Pins 8 & 10


Finally got it right ... damn

I have a Wavetek meter, if you'll send it to me I can check it out (for a small fee) and tell you if it is within spec for a 1974 2.0L MPS. Email me.

There are caveats however...

D-Jet is a good reliable FI system, but its only as good as its weakest component.
We have to assume your engine is correct mechanically - valves, compression, timing etc.
The other FI components, even though new, are also in spec.
What condition is your FI harness in? I know of D-Jet 914s' that run rich with an old ratty harness.
Even though I can tell you precisely how it compares to other new 1974 2.0L MPS, and can recalibrate yours to get it close if necessary, the only real way to best calibrate it is when it is on your car, with an exhaust gas analyzer.
Is your engine stock configuration in every respect, or were changes made at any time?

I'd like to affirm the previous two posts by SLITS and Jeff and also suggest you borrow, or even buy, the correct MPS from a running car, install it in yours, and see if that's the problem. Consult Jeff Bowlesby's diagnostic website to double check the correct application.

CG... I will be at the Great Porsche Show Off tomorrow and will bring a spare MPS you can try on your car. My 914 is also a '74 so you can compare your setup to mine.

steve

its supposed to hold vacuum for 15 minutes...

did they put the right cam in during the rebuild?
if not a cam with lots of overlap will mess up the vacuum and mess up the fuel injection since the vacuum signal is unsteady.

you may have to go to carbs or reopen the motor if the cam is not a fuel injection grind.

brant

Brant - from what I have heard, the cam could very well be the issue. I hope to see CG today and will have him post full specs of the parts used.

cool
I'm curious to see this turn out

if all of the injection parts are gone over with a fine toothed comb this should be fixable.

Hey Brant, Have you made a hard decision on CVAR at Hallett?

I haven't sorry...
definitely on my radar
I'm trying to pull together finances for a tow to laguna seca and depending on how that finalizes will probably effect tows east.

I would suggest that you pull the computer and remove its connector and then use an ohm meter to probe your components. Do not use the ohm meter on the computer. Write down the values you measure and compare them to this list. Fix anything that is out of spec. This will also help you find any faulty or high resistance wires. Check all grounds.
Use this as a guide:

Terminal(s) Component Expected value
1 and 13 TS1 - air temp sensor 300 ohms @ 68 deg. F
3 and ground Fuel injector - cylinder 1 < 3.0 ohms
4 and ground Fuel injector - cylinder 4 < 3.0 ohms
5 and ground Fuel injector - cylinder 2 < 3.0 ohms
6 and ground Fuel injector - cylinder 3 < 3.0 ohms

7 and 15 MPS primary coil 90 ohms
(check each lead and make sure there is no continuity to the MPS case)

8 and 10 MPS secondary coil 350 ohms
(check each lead and make sure there is no continuity to the MPS case)

9 and ground Accelerator Pump Contact Track #1 10 indications of continuity from fully closed to fully open throttle

20 and ground Accelerator Pump Contact Track #2 10 indications of continuity from fully closed to fully open throttle

11 and ground ECU ground circuit Less than 0.5 ohms
12 and 21 Trigger contact switch #1 Alternating continuity as the engine is cranked
12 and 22 Trigger contact switch #2 Alternating continuity as the engine is cranked
16, 24 and ground ECU power source from main power relay on regulator plate Turn key to the "on" position, read voltage, should be less than 1 V difference from voltage measured at battery terminals.

17 and ground TPS idle contact Less than 0.5 ohms when the throttle is closed, infinity when the throttle is opened more than 2 degrees.

18 and ground Start signal from ignition switch Turn key to "start" position, read voltage, should be greater than 12V.

19 and relay plate terminal III (white plug, back left corner) ECU control line for the fuel pump relay Less than 0.5 ohms

23 and ground TS2 - CHT, cylinder head temperature sensor > 2K ohms at 68 deg. F for all but 1973 2.0 L, > 1.2 K ohms for 1973 2.0L

First of all thank you all for your help!!!!!!

I hope I find all the points of checking the fuel inj harness!
Should I be able to get it right by cleaning all the connections?
Or does somebody might have a working harness?

Then back to the question of the cam,
It has the WebCam .255 duration and 430 lift for stock fuel inj
but I do know it is supposed to work

tradisrad are you in the area?

Steve thank you for your help!

My Plan:
- Checking the fuel pressure
- Checking Vacuum
- checking the MPS
- Checking all the connections

I so hope I get it right!

yep...

double check EVERYTHING... (even if the "shop" already did)
pulling the harness and going through all (is it 27?) of the connections is a good idea.

I once found one bad wire within my harness by doing that test.

do you have a noid light?... at least pull the injectors and physically view their spray patterns.

oh... if you personally haven't done it. Start with a valve adjustment and timing recheck

the description could also be a timing issue

My experience supports brant's advice. To elaborate for the less experienced like myself:

There is an optimum range of resistance for the various "fuel injection" components. You can determine the resistance at the component, but, checking the resistance values from the multi-pin terminal that connects to the black box (ECU), after pulling that terminal from the ECU, helps verify the status of the wiring in addition to the component being checked.

Fuel delivery on this car seems extra sensitive to the various timings. Checking valve lash, dwell and ignition timing is the logical first step.

I think it's important on this car to use a dwell meter and timing light. I've never gotten a good gap using feeler gauge alone. Setting the advance to the highest RPM by ear is dangerous for any A/C because of the peril posed by detonation, and static timing isn't precise enough.

good think that i had the injectors and the ECU rebuild by Fuel Injection Corp in Cal!

I'd still methodically test everything...
step by step using the brad anders website.


I'd verify everything anyone else did with my own eyes before I would rule it out

I feel your pain
I chased a gremlin for months one time
the car would idle and start great in the driveway and then within 2 miles it would die.... I went through everything

changing components out is an option, but its really better to just go through and eliminate through testing.

brant

Do you have stock or hydraulic valves?

stock know

Hmm, that may be the problem. I don't know that much about cams but looks like that profile is for hydraulic

CG-914, I am not in the area. I am just south of San Francisco.

Have you pulled the computer connector and probed all of your components yet? Did you find anything that is out of spec (when compared to the list I posted)?

Jeff Bowlsby makes a reproduction harness. Jim Kelley has been selling lots of stuff and he had some harnesses. BUT, don't go replacing anything until you have probed the components.

If you find something that is out of spec, i.e. high resistance, clean the connectors to that component and then recheck.

Brad Anders has a great web site that talks about the d-jet and he goes over tuning the MPS. I would not mess with the MPS until every thing else has been confirmed good.

And if your cam is supposed to work with the D-jet then I would simply assume that it is good and that should be your very very last thing to rule out.

Have you checked for intake vacuum leaks, Spray pattern on each injector, are all plugs firing? do you have points and if so are they gapped correctly? Engine timing set to 27 degrees at 3500 rpm?

It's a lot, but you can do it all your self! edited for unfair bashing of shops.

tradisrad

Everything you wrote is good info except the last sentence. Repair shops come in all colors but that generalization is horribly unfair to good people, some of whom are generous enough to offer free advice on this board.

good point.

there are a few shops I would absolutely take at their word

jon larson
mark's
ajrs
more


but there are many many shops I wouldn't let touch my car

ok. my apologies. I can see how that is a crappy thing to say. i'll edit it out.

I'm a full time student and I work 35 hours a week
so this afternoon is the first time i'm gonna get to it!



I will keep you guys up to date!

Steve and I just worked on my car. The fuel pressure is set at 29 - 30 psig so good!

We found out so far is, that the car does NOT go over 3000 rpms!

The timing is set on the car at NO ° at 3000 rpms.

Does anybody experienced an issue like that?

I still will check the harness...

Do you mean its timed at top dead center?

yes top dad center or 0°

but the engine at ALL does not turn higher then 3000

Timing Should be 27 degrees @ 3500 RPM

i would like to set it there but i cant turn the engine that high!

Retime it to 27 before top dead center @3000rpm with distributor vacuum line unpluged and capped.

Are you sure your using the #1 plug wire? Drivers side rear plug?

the fuel harness is wrong connected, so I'm trying to fix that first! Then I try again! I also need to go and by a timing light, my buddy just left with his!

When it is @TDC, what is the relative position of the rotor & where is the mark on the dizzy that shows #1 firing position?

What is the easiest way to get the body beneath the throttle body out?

Wich is the sensor under that body?

Let me chime in...
The timing looked fine to me though the engine will only rev to 3000rpm. There is a yellow mark that, if marked correctly, is 27* BTDC and at 3k rpm was positioned at the notch. Vac adv was disconnected.

I had to leave so couldn't help troubleshoot more but there are a couple things I recommended he look at: make sure the FI harness is correctly grounded and check to be sure the injector connections are in the correct order. I noticed his harness is routed around the front of the motor instead of the rear and it's very possible the injector connections are swapped.

You're going to have to loosen or perhaps remove the intake runner bolts at the head to remove the plenum.

Thank you steve!

OK: How is this sensor called?
Click to view attachment