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

[8716valver]

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 -

[sdezego]

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.

[8716valver]

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?

[sdezego]

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

[8716valver]

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.

[8716valver]

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.

[8716valver]

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.

[Wesley Brown]

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!!!

[9aba16vt]

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...

[vwmk1gti]

try unlpugging o2 sensor and see if its the same
fuel filter clogged?
transfer pump ok?
full throttle switch ok?

[8716valver]

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.

[ps2375]

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.