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MPS and other problems

I'm having some drivability problems with my '74 2.0 L. The engine wants to die whenever I come to a stoplight or have to remain at idle (this happens when AAR has fully closed). I have replaced the throttle position switch and it is adjusted properly. This phenomenon used to be a rare occurance, but now is almost every time I let the engine idle. All sensors are reading the correct resistance as per Kjell and Brad Anders' articles (thanks guys). I have tried adjusting the mixture knob on top of the ECU with little success. Also have adjusted the MPS richer and leaner with no permanent success. I am at a loss as to what to try next. Maybe a BFH!

I seem to think that I remember that a sick MPS will cause difficulty with the transition between idle and off idle. Is my brain working correctly? So I finally check to see if my MPS matches what Mr. Anders says that it should be for a '74 2.0L. The Bosch number on my MPS is: 0280 100 001. It is supposed to be: 0280 100 043. The VW number on mine is: 311 906 051 B and should be: 039 906 051. This is close but not the same. The housing on my MPS is also a little different from the pix that I have seen.

BTW, I have had this car for 11 years with the wrong MPS and it has driven fine most of the time. The ECU has a very worn sticker on the back that says "Remanufactured for Volkwagen of America". I can't find any numbers on the ECU.

Anybody have any thoughts or ideas as to what may be causing my idle problems or information on those MPS numbers?

Sorry that this is so long.

Thanks

David Pritchard

Last edited by Pritchard; 10-16-2002 at 04:29 PM..
Old 10-16-2002, 04:26 PM
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Been driving that long on a MPS for a type 3 (Squarback or Fastback)? Get yourself the right MPS to solve the problem, or if you are real good with tools and such adjust a good used one (1.7 or 2.0L) to the 74 spec's per Brad's page.
To see what ECU you have pull the plug and look inside as there is a tag showing the model #.
IF ALL FI parts match the car should drive nice and smooth, if not matching you have problems.
Usually, problems with off idle to partload are caused by worn TPS or mis-adjusted TPS. This is assuming everything else with the FI is kosher.
Geoff
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Old 10-16-2002, 05:35 PM
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How's the ignition? Ignition is always the first step in troubleshooting driveability/FI problems...

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Old 10-17-2002, 07:56 AM
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ignition stuff

I have recently (w/in three months) replaced plugs, wires, coil, rotor and cap, and readjusted the Ignitor. It took two sets of new wires to get all four to fire properly. I still wouldn't bet against the ignition being part of the problem. The dizzy has virtually no lateral movement in the shaft. The weights move freely and nothing appears to be overly worn or out of place. Is there something else that could be wrong with the dizzy? BTW, FI trigger points are less than 1000 miles old.

The TPS is brand new and adjusted properly. I checked for proper operation at the ECU plug and it is OK. I haven't noticed any model numbers inside the ECU, but I'll check again.

So I have a Type 3 MPS. Anyone got a MPS for a '74 2.0L they want to get rid of?

I appreciate the info.

David Pritchard

PS- The car is running perfectly today. It must know that I am about to shoot it!
Old 10-17-2002, 10:23 AM
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I was having the same troubles on my 76 2.0, and by disconnecting spark plug wires i found 2 cylinders were not firing at idle, 2 that fire together by the trigger contact points. since you have new ones, it may be a ground or connector issue causing the same results, maybe?

I also just found out i had (for 20 years) a 1.7 mps (now deceased) in my 2.0, and all of a sudden I know why i burned some valves in it. Funny, I always thought it was because I had a header muffler on it. I don't have many miles on it since a rebuild, so i'm glad i caught it before i fried the new motor.

Along these same lines, Anyone know if a 1.7 motor fitted with 2.o crank and pistons whether the injection system can be tuned out to work properly with it. I have an extra set of 2.0 injectors if that would help.

PD
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Old 10-17-2002, 04:48 PM
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Thanks

I'll check those trigger points. If the trigger points were not operating properly, that would explain the "ignition" trouble I have been experiencing. This is buggin' me, why would the trigger points only cause trouble at idle?

Let me see if I have the trigger points adjustment procedure correct in my head: center the points to have equal gap on both sides, check for continuity (alternating sides) when rotating the dizzy shaft. Is this correct?

DP
Old 10-17-2002, 05:11 PM
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Pritchard,

I have a similar problem with my 2.0 and I have the correct MPS. In fact I have three of them. One I use for getting past emmissions, the other checks out in all ways per Brad's data (but still fails occassionally as you're describing), the third doesn't hold pressure so I was going to have it rebuilt.

I think you're analysis about the MPS is correct. Mine will also act this way if I turn on the AC, which indicates to me that under additional load at idle when pressure increases, the MPS is failing somehow and the RPMs drop significantly - almost stalling.

If you're interested in the one needing a rebuild, I'll give you a deal on it. It will then cost approx $200+ to get it rebuilt. I had the info on the place in CA that does these but can't locate it at the moment. Anyone want to chime in?

Let the fun continue!
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Old 10-17-2002, 05:18 PM
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I have seen the 1.7 style FI used on a 2.0l motor using the 2.0l injectors work fine. I would also install a later larger bus TB (same size as a 914 2.0l) supposed to be pretty much bolt on. I have one laying around if you want it.
What are you going to use for the MPS? The setup I saw had a 037 MPS along with the 73 ECU. A 049 MPS off the 1.7 will be lean at WOT.

3D914- Does the MPS leak down slowly or just not hold at all? I have cafefully taken them apart and resealed the paper gasket under the diaphram with a light layer of Permatex Motoseal. Clean and check the rubber o ring.
Geoff
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Last edited by Bleyseng; 10-17-2002 at 05:34 PM..
Old 10-17-2002, 05:30 PM
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Trigger points were fine

Just checked the trigger points. They checked out fine. I will have to wait till tomorrow to check the signal at the ECU plug.

3D914, if all the FI stuff checks out, I will get in touch with you about the MPS. I need to recheck mine to make sure that it will still hold a vacuum.

The search continues.

DP

PS- engine ran perfectly today. If I keep on posting, maybe it will continue to behave!
Old 10-17-2002, 06:10 PM
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Hi, you and I have spoken via email on this issue, a few more things...

1. Make sure that this problem isn't due to a mechanical or ignition issue. Valves should be adjusted to spec. Compression should be over 100 psig with no more than 10 psig variation. Idle vacuum should be at least 14 to 15 in. Hg when fully warmed up. All ignition components should be carefully checked and renued if necessary. Plugs should be gapped to spec, and timing and dwell set properly.

2. All vacuum hoses should be checked for integrity, as well as any suspicious parts (e.g. throttle body gasket, injector seals, plennum). Fuel pressure set to spec, new fuel filter. Pull the injectors and as per Kjell's article, check each one for spray pattern, leaks and flow.

3. Check ALL components numbers in the FI system as per my web page. Replace any components that are not correct. Check all sensor resistances hot and cold. ESSENTIAL - verify that the MPS holds vacuum without leaking, see my articles for details. Verify TPS is set correctly. Set idle CO with the ECU pot using a gas analyzer, not your nose. Set idle speed with the air bleed screw.
Old 10-18-2002, 08:48 AM
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Bleyseng,

Of the two that I have (that are not on the car) -
1) Fails to hold pressure at all.
2) Holds pressure until it gets warm, then drops 5 in.hg. in less than a minute. Once it cools down again it will hold with no variation, Weird uuhh! And this is the one I use to pass emissions.

I'm going to have one of them rebuilt for my new engine. I'm tired of guessing on this stuff.

Enjoy!
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Old 10-18-2002, 06:15 PM
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Pritchard- after rereading your posts i'd try to determine the true nature of your problem. when it acts up again, with the engine running unplug the spark plug wires one at a time to see which ones make the engine slow down or have no effect. if there is no effect, check for spark at the plug. if there is spark, then switch the injector plugs temporarily to see if it moves the problem to another cylinder. at least you'll know whether it's a fuel problem or a spark problem and can proceed from there. and if it's in a paired pattern of 1/4 or 2/3 then that's another clue.

Bleyseng- the one that's on the car i can't read the number but it's a 72 1.7, so it's probably the 049 mps. can i adjust out the wot setting to correct it, or should i look for a different mps?

How much do you want for the Throttle body?

PD
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Old 10-19-2002, 04:29 AM
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