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    Thread: Digi 1 16v N/A Lean "Burp" Under Acceleration

    1. Member 8716valver's Avatar
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      06-15-2012 09:27 AM #1
      Ok I've had this system installed for a few years now and it's been running awesome until just recently when started to run funky. It's chipped for 16v N/A and I have Vac, WB, and FP gauges installed for monitoring....no ISV.

      Closed loop acceleration is where it gets wierd. I can be cruising at any speed and run about 14-15afr BUT as soon as I dip into the throttle slow or fast I get this lean spot 16-18afr for about 1sec. After that it settles anywhere from 12 if WOT to 14 under continued acceleration.

      Yesterday, in an effort to remedy the issue I did some maintenance.

      Here's what I found/did.

      1. Checked ECU grounds
      - Found that larger gauge ground to the head was cracked in a couple spots. I spliced into the existing wire near the ECU and connected back to the head with a new terminal.

      2. Checked CO Pot
      - It was totally fried and not giving any resistance value! Luckily I had a spare so I installed that one and dialed it to 450ohm.

      3. Checked Vac Lines
      - All my lines are 3yrs old and they still look brand new. Pulling 20 in the vac gauge at idle...

      4. Checked fuel pressure and fuel system for leaks.
      - FP is 50psi and I did not find any sign of leakage


      So any advice or tips??

      Pic for clicks -


    2. Member sdezego's Avatar
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      06-15-2012 09:43 AM #2
      That is called "Digi Lag". It is normal with most of the chips out there. SNS used some of VWMS (or Rallye) code to rid the chip of that. Not sure who else these days did as well, but I know the 4 other manufacturers chips I had back in the day all had it.
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    3. Member 8716valver's Avatar
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      06-15-2012 10:58 AM #3
      Quote Originally Posted by sdezego View Post
      That is called "Digi Lag". It is normal with most of the chips out there. SNS used some of VWMS (or Rallye) code to rid the chip of that. Not sure who else these days did as well, but I know the 4 other manufacturers chips I had back in the day all had it.
      Thats one possibility. But why didnt it do it over the past couple of years? This lean condition just started after I replaced my CO Pot with a known good one.

      Should I try and adjust the CO Pot more rich?

    4. Member sdezego's Avatar
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      06-15-2012 11:29 AM #4
      It is very possible that changing the CO pot amplified the affect. What Chip are you running?

      It is possible that w/o the CO Pot, Digi stays in OL where you would not see any Lag. Was just the CO Pot thermistor giving you a 0 reading on the old one? What about the IAT terminals on the CO POT? Just curious.

      Anyway, 450 ohm (COLD) is usually a pretty good spot, but you may want to lower it and see if it has any effect. ..and possibly raise it to see if Digi is over compensating in Closed Loop just before it ticks over to OL.

      Here is a fairly good thread in case you have not come across it: http://forums.vwvortex.com/showthread.php?1860918
      Last edited by sdezego; 06-15-2012 at 11:33 AM.
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    5. Member 8716valver's Avatar
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      06-15-2012 11:37 AM #5
      Quote Originally Posted by sdezego View Post
      It is very possible that changing the CO pot amplified the affect. What Chip are you running?

      It is possible that w/o the CO Pot, Digi stays in OL where you would not see any Lag. Was just the CO Pot thermistor giving you a 0 reading on the old one? What about the IAT terminals on the CO POT? Just curious.

      Anyway, 450 ohm (COLD) (outer terminals) is usually a pretty good spot, but you may want to lower it and see if it has any effect. ..and possibly raise it to see if Digi is over compensating in Closed Loop just before it ticks over to OL.

      Here is a fairly good thread in case you have not come across it: http://forums.vwvortex.com/showthread.php?1860918
      I'm running a chip that I bought from a user on here. I believe it is an SNS copy. The thing ran sweet for years before this lean issue popped up.

      I was getting a zero reading on the outer terms of the old CO Pot.

    6. Member 8716valver's Avatar
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      06-15-2012 01:58 PM #6
      I'm going to swap the bad CO Pot back in and see if I get the lean spot to go away. It didnt do this until I swapped CO Pots and replaced the ECU ground.

    7. Member 8716valver's Avatar
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      06-15-2012 03:02 PM #7
      Heres what the car is doing. This was 4th gear cruising at 40mph then stepping on the gas and holding until the digi richened back to acceptable afr.


    8. 07-15-2012 02:07 AM #8
      Change your O2?
      Check for bad ground on O2
      IS TP sensor working properly and showing vary in resistance during range .
      Vacume leak?
      Vacume leak to FPR?
      Just a thought.
      I have had fuel pumps show good pressure while idleing but lean while driving . That would explain a lot lean during exceleration .

      I'm hoping to do this swap and I need your help on getting a DIGI1 on my 87 scirocco 16v . Hopefully I can get it all figured out on the harness and parts needed for a NA swap!!!

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      07-15-2012 12:36 PM #9
      off subject...

      dont have your intake tube put pressure on your trans cable like that..
      its pulling the cable, like youre pressing the clutch slightly, making the clutch surface not fully engage, furthermore causing slippage...

    10. 07-18-2012 01:10 AM #10
      try unlpugging o2 sensor and see if its the same
      fuel filter clogged?
      transfer pump ok?
      full throttle switch ok?

    11. Member 8716valver's Avatar
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      09-13-2012 02:31 PM #11
      Quote Originally Posted by vwmk1gti View Post
      try unlpugging o2 sensor and see if its the same
      fuel filter clogged?
      transfer pump ok?
      full throttle switch ok?
      Been busy getting married this summer and haven't had the chance to eff around with this much.

      Back at it now tho

      I've replaced the O2 sensor with new...No change
      Checked fuel filter...Squeaky clean
      Have not checked tfer pump.
      WOT switch is good.

      I can drive the car with the WOT switch tripped. It will hold about 12 on the afr no matter what.

      Im thinking my issue may stem from timing because I remember on the days leading up to when this BS started the car was backfiring slightly on decel.

      So tonight I'm triple checking my mechanical timing.

    12. Member ps2375's Avatar
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      09-13-2012 05:37 PM #12
      Quote Originally Posted by 8716valver View Post
      Im thinking my issue may stem from timing because I remember on the days leading up to when this BS started the car was backfiring slightly on decel.
      That sounds like it might be slightly rich on decel. I can make my MS do that if I add fuel to those bins, and when my car was still on CIS, it always did it, as there was no fuel cut on decel.
      Tradition is the art of making the same mistake repeatedly, on purpose.

    13. Member 8716valver's Avatar
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      07-22-2013 09:53 AM #13
      Bumping this up again. Still haven't solved the issue and frankly, I haven't really touched the car in quite awhile. This week I plan on checking mechanical timing tho.

      I should note that the car will spike lean and almost stall just after it runs for 15sec or so. It cannot be run unless the WOT switch is tripped.

    14. Member sdezego's Avatar
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      07-23-2013 11:38 AM #14
      Quote Originally Posted by 8716valver View Post
      I should note that the car will spike lean and almost stall just after it runs for 15sec or so. It cannot be run unless the WOT switch is tripped.
      By holding the WOT switch, you are sending the ECU into open loop and ignoring the 02 feedback. It looks like Digi-Lag in form, but does look waaay exacerbated. Check 02 wiring and ground there. Also, make sure the 02 heater circuit is op. You may want to configure the output from your Innovate to simulate the NB signal to Digi. This way, you know what you are seeing the gauge is what is being told to the ECU.

      Have you made sure that the ECU line it proper diameter, length (And More Importantly) on the correct port on the TB? Wrong port is a very common mistake that will wreak havok on accel.
      Last edited by sdezego; 07-23-2013 at 11:41 AM.
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    15. Member 8716valver's Avatar
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      07-23-2013 01:33 PM #15
      Quote Originally Posted by sdezego View Post
      By holding the WOT switch, you are sending the ECU into open loop and ignoring the 02 feedback. It looks like Digi-Lag in form, but does look waaay exacerbated. Check 02 wiring and ground there. Also, make sure the 02 heater circuit is op. You may want to configure the output from your Innovate to simulate the NB signal to Digi. This way, you know what you are seeing the gauge is what is being told to the ECU.

      Have you made sure that the ECU line it proper diameter, length (And More Importantly) on the correct port on the TB? Wrong port is a very common mistake that will wreak havok on accel.
      I don't think Digi-Lag is relevant here only because it ran perfect for years before this issue developed.

      Interesting idea with the WB hookup and I might actually do that while i have my console out.

      I should note that I did replace the O2 sensor with a new Bosch unit and still didn't notice any difference. It runs the same even with the O2 unplugged.

      I'll quadruple check the vac line but IIRC it is 1 meter long and is plugged into the nipple which is downstream of the throttle plate.

      Thanks!

    16. Member 8716valver's Avatar
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      10-17-2013 11:17 AM #16
      Bumping this because I'm still having this problem although its worse now. I haven't driven the car in like a year because of it.

      As soon as I start the car it slowly creeps lean until the engine stalls from lack of fuel (or combustion).

      Just to recap, I've wired in a brand new bosch O2 sensor with a fresh ground to the tranny ground and saw no change. Confirmed my tbody switches are functioning. Changed my ecu vac line to a hard line that is the same inner diameter as the tbody nipple. Verified that fuel flow is not being blocked and the pump is giving proper pressure.

      What I did find is that my cts and distributor plugs have exposed wire from the insulation cracking over the years. If anyone has good pigtails for these feel free to sell them to me asap

      I don't think its an ignition issue because the engine seems to run smoothly and

      Next steps:
      Triple check mechanical and ignition timing again
      Wire in good pigtails for the distributor and cts
      Check and replace any suspected faulty ignition components
      Possibly use wideband O2 output signal for ecu O2 input
      Might change out the injector harness

    17. 10-21-2013 12:42 AM #17
      Just a thought have you checked the fuel flow/ pressure? My caddy does this same thing, I have a custom fuel cell (alloy) and even thro I've drained it and cleaned it a hand full of times I still get a few shaving. ( we had to modify it after the sending unit after it was built). Every time it does it I pull the filter clean and off I go.

    18. Member 8716valver's Avatar
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      10-22-2013 08:22 AM #18
      Quote Originally Posted by fvtec View Post
      Just a thought have you checked the fuel flow/ pressure? My caddy does this same thing, I have a custom fuel cell (alloy) and even thro I've drained it and cleaned it a hand full of times I still get a few shaving. ( we had to modify it after the sending unit after it was built). Every time it does it I pull the filter clean and off I go.
      FP is running about 52psi at all times and the filter is squeaky clean.

      Tonight I plan to wire the WB output to the ECU O2 input. Not really expecting any change but at least I can remove another potentially faulty device.

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      10-27-2013 08:41 AM #19
      Whats really funny is, I am going through the saaame exact thing! I am just to lazy to post it.
      I have tried new o2 sensors, ecm, bought and havent installed WB, checked grounds for o2, everything... Haven't checked filter my filter yet. I set my ignition timing back to 6 btdc but the car runs like crap... I have to set it to like 10 atdc ti get it to run ok... Im am T though.. I unhooked it to solve the issues before I detonate again like years ago. I have noticed that when letting it sit at idle and after normal operating temp, the car will start bucking and idle hunting like it starts loading up with fuel.. (loads of rich smoke)
      Ive even put a new alternator because of the fuel enrichment due to low voltage, different gel cell batteries.. too many changes to list..

      Wtf is wrong with digi!?

      The last thing I think it could be is the distributor.. when it gets hot, it acts a fool...?
      IDK

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      10-29-2013 07:42 PM #20
      I loved the idea of this set up but got tired of trying to work the querks out of it. I could never get my air\ fuel to where it should be. My wife's Cabriolet now has an ABA in it but I may give it another try in my MKII.
      Last edited by waterwagon; 10-29-2013 at 07:48 PM.

    21. Member 8716valver's Avatar
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      10-30-2013 10:48 AM #21
      Well I believe I've got it running a lot better now. Here's a vid of the AFR at idle with the engine up to temp. Let me know what you think.


    22. Member 8716valver's Avatar
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      11-08-2013 11:39 AM #22
      Took it out for a ride last night and it runs nice and strong again. Forgot how much this engine loves WOT. I ended up replacing Bosch water temp sensor, injector harness, spark plugs, cap, and rotor to get the power back.

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      11-19-2013 01:53 PM #23
      I think my culprit finally showed its face.. it was the ground on the battery.. when hot, I would guess the load from the fan would cause the connection to vanish causing the ecm to dump to prevent detonation.. havent solved it yet but I will confirm in a day or two. .

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