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debugging hesitation and poor running
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924RACR  



Joined: 29 Jul 2001
Posts: 8278
Location: Royal Oak, MI, USA

PostPosted: Fri Nov 22, 2002 10:31 am    Post subject: debugging hesitation and poor running Reply with quote

Just re-flowed the solder on the DITC and adjusted the throttle position switch. I was having trouble with rough pickup off idle and at throttle positions from 5-10%.

Will let ya know how it has worked...
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Vaughan Scott
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924martinirossi  



Joined: 04 Nov 2002
Posts: 605
Location: Seattle, Washington, USA

PostPosted: Fri Nov 22, 2002 7:22 pm    Post subject: Reply with quote

Need to know if that is the "big black box" under the steering column or the one that sits foward of the shifter?

Michael
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924RACR  



Joined: 29 Jul 2001
Posts: 8278
Location: Royal Oak, MI, USA

PostPosted: Fri Nov 22, 2002 11:58 pm    Post subject: Reply with quote

The one under the steering column is the fuel/lambda thingy; the one under the R2D2 unit (HVAC) in front of the radio/shifter is the DITC ignition controller, which I've been playing with.

I found it had a white residue on it (on the circuit board). Talking to my crew chief, who moonlights as a software engineer here @ Bosch, and other SW/HW geeks here, sounds like this is the second coming of the Crystalline Entity - dendritic growth or blown cap(acitor). I think I'm going to have to pull it and bring it in for diagnosis... will have to clean it off w/ contact cleaner. Brakleen was starting to damage the plastic of the board - don't do this!

Seems like it's running better (drove it in through the snow), but it takes the course of the day to warm up enough to create/recreate the problem, so I can't make a definitive statement of results yet.
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Vaughan Scott
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wdb  



Joined: 02 Nov 2002
Posts: 2024

PostPosted: Sat Nov 23, 2002 12:37 am    Post subject: Reply with quote

I would think that since the problem seems to be throttle position sensitive it would most likely be the T.P.S. . FYI I was looking in my generic auto manual , and it says the TPS signal can range from 0.5 volts (idle)to 5 volts (wot) and a common test for the tps is to monitor tps output voltage while slowly moving throttle , voltage should rise smoothly in relation to throttle movement .if the voltage readout is eratic the TPS should be replaced .
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924RACR  



Joined: 29 Jul 2001
Posts: 8278
Location: Royal Oak, MI, USA

PostPosted: Sat Nov 23, 2002 2:05 am    Post subject: Reply with quote

That'd work great if the car were EFI. It's not, any more than it's a generic car. Just a warning to anyone trying to use generic auto info, not a flame.

In order to understand the function of the TPS on this car, or any other engine controls on the 931, you must have the factory manual for the 931. Sorry, nothing else comes close. The factory manual explains how to adjust the TPS.
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Vaughan Scott
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Sat Nov 23, 2002 5:12 am    Post subject: Reply with quote

Drove the car at lunch; previously by this time during the day the hesitation would have shown up. No signs of it, except a minor hesitation just below 3000rpm. I suspect that's the kind that can be dealt with by tuning. Much improved, very happy. Still have to replace those orange o-rings in the intake tract to seal it up - can see the oil leaking out under boost - but they're on order.

So, it seems that the re-flowing of the solder was a good thing! Not sure I'd recommend it to everybody, but it worked for me... that and adjusting the TPS.
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Vaughan Scott
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Tue Nov 26, 2002 11:11 pm    Post subject: Reply with quote

Still waiting for the leaking seal replacements. However that has not stopped me from dinking around with the tuning! Think I've got the mixture half-decent, where it runs fairly smoothly. However I was having an odd time of it yesterday; I had the air temp sensor removed and connected, and I had the lambda disconnected. I was unable to see the timing move at all when I was adjusting the idle, although it did seem to be adjusting the idle for me. I have seen this work on the other (81) 931. So, I'm a little worried about the state of the DITC - though I did clean it off again, this time with the proper circuit board cleaner from Radio Shack.

I am going to check it again with the timing light with everything connected tonight, see if I can see it moving the timing; if it doesn't, I'm going to try swapping in the DITC from the 81 and see if that helps. The only other thing I can see doing is trying a new crank sensor.

Anyone else see anything I'm missing?

Car runs mostly OK, just a bit of the hesitation and a little rough down low, it's OK once it clears its throat and gets on the boost. As mentioned, I do have the remaining seals and hoses on order that should resolve my leaks.

It's kind of amusing, looks like one car has an ignition problem, the other has a fuel problem! Ugh.
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Vaughan Scott
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Lizard  



Joined: 03 Nov 2002
Posts: 9364
Location: Abbotsford BC. Canada

PostPosted: Wed Nov 27, 2002 3:07 am    Post subject: Reply with quote

I actually just picked up an 81 VW Rabbit for $400cdn w/ CIS and it uses the same distibuter cap and rotor as out cars, it was hesitating really badly in the low end but once it got above 3000 or so rpm it ran fine

the only problem he had listed was that the downpipe was broken off, it was hesitating and the clutch was having some issues, so I fixed the clutch in 10 min while I was there and then put day insurance on it drove it home, I am going to do the clutch a tune up and get the exhaust fixed and then put insurance on it for the winter

well loosened off the bolt on the distributor got a friend to start it up and then turned slowly about 1/4 turn, and then it al of a suddon started running ALOT better it was actually running w/ very little hesitation, but it was still hesitating, so I pulled the cap which I found had been put on backwards, this had destroyed the rotor and the points inside the cap, so $20cdn later replaced those, and it was running almost perfectly, but not quite, pulled the plugs and saw some glazing on them so I am going to just get new plugs and get some new wires just because I am sure it will be fine

basiclly I am saying make sure your spark is good
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Wed Nov 27, 2002 6:15 am    Post subject: Reply with quote

Well you're right in looking at the spark, but I'm having issues with that. Mainly, I believe, in the electronics - though sure, it could be the coil. Car crapped out on my today, left me hanging.

I suspect it might possibly be a flaky DITC unit or crank sensor. I'm going to try swapping them from my other car. Sure, it could also be a weak coil too. Everything else is new, already replaced them long time ago - cap, rotor, plugs and wires. Nothing but the best, of course. Likewise new fuel pumps, accumulator, and filter. However the fuel pump fuse was the wrong size, it turns out. That was part of the problem, very annoying, why it died today.
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Vaughan Scott
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924martinirossi  



Joined: 04 Nov 2002
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Location: Seattle, Washington, USA

PostPosted: Wed Nov 27, 2002 6:25 am    Post subject: Reply with quote

Well!! I finally figured out kept my running so poorly. It all had to do with the fuel mixture on the fuel distrubitor. I slowly turned it CW untill the 2,6K - 3,6K Rpm stumble went away. As you turn this CW you will also have to turn up the throttle idle speed screw. The car flys now!

Michael

Vaughn, I also have some info on the DTIC that you might want to post in the electrical section..
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Wed Nov 27, 2002 11:25 am    Post subject: Reply with quote

Ah, so it was running lean? How's your idle now? Mine was rough and erratic until it died and flaked out on me.

Please email over that info. I would greatly like to post it, not to mention for my own info. Ironic. I work at Bosch, my crew chief is a EE (Electrical Engineer) working on software and hardware, and we can't quite figure out much of what makes this thing tick. Well, I'll have to take the manuals in, see what we can do with them.
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Vaughan Scott
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Wed Nov 27, 2002 11:41 am    Post subject: Reply with quote

There was also an issue with the fuel pump fuse I mentioned... wanted to clarify... it was an undersized fuse apparently, was getting very hot, maybe bad connection at the fuse, maybe not, seemed to be a major issue.

I'm hoping that's the real reason the car died.
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Vaughan Scott
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924martinirossi  



Joined: 04 Nov 2002
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Location: Seattle, Washington, USA

PostPosted: Wed Nov 27, 2002 1:00 pm    Post subject: Reply with quote

Jumper power from fuse 9 to fuse 2 on the additional fuse board. If car runs OK (like mine did) then check the terminals where the relay plugs into. Also I had a bad ground fron the connector too.

8.24 Amps at 12+Vdc at the pump termainals is OK. I would be interested in getting a new pump to measure the current and volts after it is installed.

Michael
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Thu Dec 19, 2002 12:03 pm    Post subject: Reply with quote

Figured out the answer to the odd throttle response today, I'm pretty sure - haven't test-driven it yet, but testing in the driveway is quite conclusive IMHO.

It's the DITC. I swapped in the DITC from my 81 into the 82, and it runs fine without dropping out. Crap.

I'm going to have my crew chief, who's an Electrical Engineer with me @ Bosch, take a look at it, see what we can find...
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Vaughan Scott
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924martinirossi  



Joined: 04 Nov 2002
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Location: Seattle, Washington, USA

PostPosted: Thu Dec 19, 2002 12:10 pm    Post subject: Reply with quote

Have you ever been sucessful at measuring duty cycle using the connector on the fenderwell? Or measured it at the frequency valve?

Michael
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