All,

I had a bad MPS sensor in my 73 2.0L. The symptoms were that the car ran very rich, an then after warm, had a very low idle.
At startup, it would idle fine, but high at at about 1500/1700 rpms until warmed up. Then it would drop to a few hundred RPM.
The exhaust smelled of fuel, and gas mileage was very poor. When I pulled it out, it would not hold a vacuum at all.

I got a replacement MPS that holds a vacuum, and replaced it, making sure that the part number is the same, and correct for the 73 2.0L, and now have some very different issues. At startup the car will barely idle, at 100/200 rpm, and stalls repeatedly. When I initially started the car after replacement, it seem to be spitting fuel from the exhaust, my intial thought was this may have been residual from the uber rich running previously.

So I went for a drive, of a few miles, the car runs well, no smoking and the smell of fuel was gone, but the idle was really low between 100/200 rpm at the stop lights. The car kept running but was close to stalling on a number of the stops along the way. At the last stop sign it actually did stall.

Once back in the driveway, the exhaust was dry, no spitting of fuel like at initial startup (pretty sure this was residual from the rich running previous to the MPS replacement). While the engine was running I popped the engine lid, and I'm fairly sure I could hear something like a vacuum leak. The car was barely idling, and "hunting" a little. When I burped the throttle cable, it stalled.

I'm wondering if the car's idle was adjusted to the bad MPS, and now that the MPS is replaced, that adjustment is way out of whack?

Or the correctly functioning MPS is now highlighting some other vacuum leak that was masked by the bad MPS previously?

Looking for some troubleshooting steps to try to sort out the idle issue, and if possible verify that my mixture is correct?


Let me know what you think.
Turk

Is it a reman unit? I've not heard too much good about them. Those a.m. diaphragms are a bit jerky but shouldn't cause a rich/low idle problem. I'd start with a tune up, set timing, valves, adjust idle air and mixture then see how it behaves.

An engine can be tuned bad to compensate for something else bad. check the dwell, and timing to confirm. Remove the plugs and check for fouling. Verify everything.

thanks guys, its not a reman unit, its an unmolested used unit.

If you have a vacuum leak in a DJET (assuming that's what you have), the idle should be higher than normal. Reason being the MPS will sense lower vacuum and assume you opened the throttle.

Also with the new MPS, to really tune the FI, you need to get an oxygen sensor to check the air-fuel ratio. This is what most modern FI systems do full time.

I agree with others to check all parts of the ignition system, valves, as well as fuel pressure.

Maybe open up the idle bleed screw a little?

--DD

That's the first thing I would try to do.

So you have a parts matching 73 2.0L setup? 037 ECU, 017 CHT and a 037 MPS??

yep, +1 on that. How much fiddling have you done w/ the bleed screw and control unit?

Don't forget the CHT sensor ballast resistor!

I do have the 037 ECU and 037 MPS, but I'll have to pull the CHT to verify.

This morning when I started it, its running very rich at cold start, fuel spitting from the exhaust, and barely able to idle.

When I pull the vacuum tube from the MPS, the car immediately idles normally, and the exhaust stops spitting.

I'm wondering if I have a bad CHT. Looking online, I didn't see anyone selling an 017 CHT (at least by Part Number). But I'll pull the current CHT, and see what I've got in there...

And I'll check the Idle bleed screw as well.
Anything else?

thx, Turk

One other thing I noticed is that the ECU dial on the top was fully counter clock wise, it was a full 20 clicks Clockwise to the other stop.


I believe the CCW stop is full lean correct?

I can't remember but in general, it shouldn't be set to the extreme setting.
Do what others have suggested first and make sure timing is set correctly before anything else.

I wouldn't pull the CHT sensor just to look at it. I've stripped them before and it's no fun.

--DD

Since it improves with the MPS disconnected, it would appear that the MPS is still giving a full rich signal. You likely have a stuck injector, too as you should not be seeing gas out the tail pipe. Start with the MPS, though. Your non-leaking one may have another failure mode.

The car should not run at all with the MPS vacuum tube disconnected. If it idles nice without it, the fuel in being supplied somepther way - like was said - leaky injectors or CSV, bad CHT or?

If you want to send me the MPS I'd be willing to check it out to see if its in spec, no charge, and return it. I could eliminate the MPS as a possible suspect.

Jeff, PM sent.

You guys probably don't remember but a while back I posted a thread asking why I had this extra sensor. The overall belief was that it was a second CHT sensor, and it wasn't connected.

(here's the thread:) http://www.914world.com/bbs2/index.php?sho...=192467&hl=

I'll check that tomorrow, I may first disconnet the one that's connected, and connect the unconnected one, to see if it may be part of the problem.

I do think the 'tuning' of the engine is basically done to compensate for the original bad MPS, and I have to to verify the timing and dwell as was recommened already.

Can the dwell be tested with a standard multimeter, or does it require a unique meter?

It sounds like I'll be dropping this engine this winter, to do a lot of the jobs that really need to be done to assure that everything is up to snuff.(sounds like I'm asking for gift certif's this christmas).

Turk

Ok,

did a couple of things this morning to try and get a little more data.


MPS | CHT | Idle
-------------------------------------------------------------
1. Y | Y | Poor Cold and Warm Idle (100/200 rmp)
2. N | Y | Better Cold Idle (700/800) Poor Warm Idle (100/300rpm)
3. N | N | Engine Dies as soon as CHT is disconnected

I tried what I believe is the second CHT (see link above)
4. N | Y | Engine runs.. barely

When re-connecting the original CHT lead, like #2 above, the cold idle improves.


So I checked the ohms on the two CHT's while connected to the harness. (Unfortantely I did this after running the engine
for the above tests, so if I need to re-do those while cold, let me know)

Orig CHT - .380 ohms (EDIT: checked this after the engine cooled - orig CHT is 1.105 ohms)
Second CHT - .812 ohms (I suspect the engine was warmer for this test then the orig CHT test above.)


Let me know if this gives you any ideas.

thx, Turk

EDIT: rechecked the orig CHT above: 1.105 ohms cold...seems wrong...

ECU knob is set at center, correct? IIRC, that only affects the idle.

Yes, I put it back to the middle, 10 clicks.

You need a dwell meter to check dwell.

I have no idea what any of that 1234,nnyy,ny means. Please splain.

The knob on the ecu is dependent on the tps being set correctly.you must first set dwell, timing, and valve clearance, our you just chasing your tail. Go to Brad Anders site and read the section about testing the system.

When you say "MPS unplugged", are you talking about the hose to it or are you talking the electrical connector?

The signal to the fuel injectors goes through the electrical part of the MPS. If the electrical plug is disconnected, the injectors shouldn't open at all. If you have the electrical plug unplugged, check the injector signals with a "noid" light. Or just unplug the electrical connectors from all four injectors and see if that makes any difference.

Something is really weird here, either in the way the fuel system is set up or in my understanding of what you are describing.

--DD

It's probably my fault, and not explaining correctly.

I only disconnected the vacuum hose from MPS, never the electrical connection.

the y/n's question explanation is for
MPS, Y=vacuum hose connected, N=vacuum hose disconnected.
CHT, Y=elec lead connected to harness, N=elec lead disconnected from harness

I'm going to send my recently aquired MPS (which holds a vacuum) to Jeff, to have him check it out and make sure I'm not introducing some other problem with it.

While that happens I will check my timing and dwell, since I need to do that anyway. (I've put the old MPS back in, even tho' I know it doesn't hold a vacuum).

Turk

OK, if you unplug the hose to the MPS it will see full atmospheric pressure and FI will interpret that as WOT. So it will command lots of fuel to go into the engine.

If that makes the car run well, it is set up very very lean otherwise, probably to tune around the ruptured MPS that was on it before. How's the fuel pressure?

--DD

I had this same issue as you described when I had my 1.7 Djet with original EFI components. My mechanic claimed my engine was running lean so he richened it up.

The idle would slowly get lower and lower until almost stalling. Ander's sight explains that it would be caused by rich idle mixture but I could never get this adjusted with the Djet. I later installed an AFR gauge and it was easier for me to adjust.

Adjusting by ear without having a sensor to reference the actual mixture does not help at all because you will foul your plugs, excessively wear the rings, foul the oil, etc. etc. And It just makes it difficult.

You should also make sure your TPS is adjusted correctly or providing the additional pulses for acceleration. Without a properly working TPS, during acceleration you may have hesitation or what may seem like almost a stalling when engaging from a stop. On my 74 bug I used to just blip the throttle twice but thats a carb.

I'm working thru this systematically. First I've sent the new (used) MPS to Jeff for testing and validation, he found that it has a moderate leakdown, electrically its fine. He's going to rebuild with one of the Tangerine diaphrams when available. I'll probably get one as well and rebuild the original at some point.

I just installed an inline Fuel pressue gauge, and its solid at 30psi, so I think I'm in good shape there.

Just recieved my timing light/dwell meter combo, so I can see where its at currently. I'll probably record those settings tomorrow, so I can see where I'm at with this current "no-vacuum" MPS.

Turk

Turk,

Any resolution to the idle problem? I am helping a friend solve almost the same problem.

Low/stalling idle but runs ok with throttle open. Real rich at idle.

After reading this thread I'm going to test one of my spare MPS and swap into his car to see if it helps. Then get a proper timing light and dwell meter on it. Among other things...mechanical.

His problem started with a wide open throttle evasive maneuver. Trying to get the hell out of someones's way. Figure it was the straw that broke the camels back.


PS. All hail Mr. Anders and his FI web page: http://members.rennlist.com/pbanders/

When I first got my 1.7 with D-jet it had a similar problem with running very rich, especially when starting. It had several other running issues but I discovered that someone had installed the cold start valve 180 degrees off (they have a directional arrow). When the valve was reversed the rich/gas smell issue was resolved. Agree with other comments with regard to doing a complete tune up.

Good luck,

Keith

No, not yet, the MPS is waiting the replacement diaphram. To be honest I've driven it quite a bit with the original MPS (that doesn't hold a vacuum), and its been running rich, but pretty well. I think the dry cold air here is helping in that respect.
My dwell is high at 53, and I think that's been done to compensate for the non-functional MPS I have. Once I get a functioning MPS, I'll redo the dwell/timing and valve adjustment to get it back to factory specs.



Kieth, thanks, that's good to know, I'll check that as well.

Your ECU has a melted in hash mark on the plastic bezel from the factory, where the knob was originally set to. Might be a good base line to go off of after Jeff gives your MPS a clear bill of health.

Valve adjustments are always a pain in the ass, but it's the baseline to start at (needs to be performed on a completely cold engine).

If valve adjustment is not correct, it will throw all the other adjustments off. IN: 0.006 in. (0.15mm), EX: .008 in.(0.20mm)


Other items to consider (some have been mentioned already):

Double check all your vacuum hoses for leaks.

Clean your trigger point contacts and also lube the cam.

Assure all electrical connections are clean and tight.

Dwell angle should be set between 45~50°

Ignition timing set at 27° BTDC around 3000~3500 RPM.