Randomly runs lean

[asb2106]

This car has been through alot of ups and downs. It rarely runs more than a few days at a time. So regardless, I just finished a 6 bolt shortblock swap on it, all went well on that front i think.. but now Im having some issues..


I drove it around 8 or 10 miles last night, made sure all was well. Seemed good.

Today I decided to take the car to work, made it about 7 miles into the drive, it started running weird, felt like a major boost leak actually, like a coupler popped off. So i shut it off, pulled over, checked it over, all looked fine.

Started it back up, ran great. Drove it to work no problems.

On lunch I drove home again, made it great all the way there, and on the way back I got about 2 miles into the drive and it started doing the same thing again, a weird chug, So this time I checked the wide band right away to see it was running really lean, 17, 18 then out of numbers saying LEAN.

Shut it off right away, pulled over, let it sit for 30 seconds, fired it back up, and it went back to 14.67. under accel it sits between 10.5-12, idle sits around 14.7, but sometimes creaps up alittle higher, 15, 15.2 maybe, then under accel goes back to 10-12 range.

So on two separate occasions it has done this now, in two different situations, first it happened while accelerating at about 50mph, second time it happened while coasting around 35-40. So im thinking I can rule out accel stuff. The rest of the 20 miles i have traveled today have been great under accel, to the point of being TOO rich.

Anyone seen anything like this? Im worried a few to many lean conditions for even a few seconds could cause some serious damage.

got my answer elsewhere.. figured I would post it here for others knowledge..

Its caused from the 6 bolt in a 2g swap, the 1g CAS triggers the misfire code in the ecu causing my problem. Turning the car off and on remedies the problem.

Now I have to find a solution to this, and not just a fix

 

[400hp93talon]

I was reading this and it wasn't making any sense....If there is a cylinder missfire(ignition problems) Your wideband is going to show it running really rich. I'm pretty sure the higher the number the richer and the lower the leaner. If you where having an injector problem which you where making it sound like it would run really lean but you just had it backwards. Because it was an ignition problem and all the excess fuel that didnt burn caused it to run rich higher number on the wideband. Are you sure you wired the cas in correctly or possibly try swapping it out with another one....they are kinda pricey if you have to buy a new one!!!!

 

[asb2106]

I was reading this and it wasn't making any sense....If there is a cylinder missfire(ignition problems) Your wideband is going to show it running really rich. I'm pretty sure the higher the number the richer and the lower the leaner. If you where having an injector problem which you where making it sound like it would run really lean but you just had it backwards. Because it was an ignition problem and all the excess fuel that didnt burn caused it to run rich higher number on the wideband. Are you sure you wired the cas in correctly or possibly try swapping it out with another one....they are kinda pricey if you have to buy a new one!!!!

im sure its wired properly.

Are you familiar with a 6 bolt swap in a 2g?

The computer will recognize a misfire, it will take the computer out of its normal operating range, and it will cause the injectors to slow down and go into a "limp" mode.

Im told its common with a 6 bolt swap, and there is a fix, using a potentiometer to increase the resistance on the barometric pressure sensor, to stop the computer for looking for misfire codes.

Its more of a work around than a fix, but Im told its common in 6 bolt swaps

and yes you are right, lower numbers mean rich, higher numbers mean lean. If you read my post again.. thats how I explained it the first time

 

[400hp93talon]

You just lost me haha!!

 

[asb2106]

haha! Im sorry, I start to ramble sometimes when i have too many things going on upstairs!

Common problem of mine

Im actually very suprised that a couple local DSM sites gave me much better response and answers than here. I was thinking this issue was perfect for this forum.

And its been up for 24 hours, with 20 views.

 

[400hp93talon]

I work on these cars for a living and built mine from the ground up so I try to help as many people as possible or atleast point them in the right direction.....and If I dont know the answer I stick around till there is one!! Ok I think I get what your car is doing.....when it is ddetecting the missfire its putting it into limp mode and the only way to shut that off is to recycle the key off to on....what your are trying to do is kee the car from going into limp mode when it does pick up the missfire correct?

Im in a car on the freeway going to Indiana so please excuse the poor spelling its hard to hit the right keys on bumpy roads!!

 

[asb2106]

, very impressive for mobile browsing

And yah, your cool man. Thanks for the input. It must be nice building these for a living.

Im sure its a ton of headaches, but pretty gratifying when its ripping down the road!

Yah im just going to trick the ECU so it wont do that anymore. Thats the plan atleast. Ill post results to show if it works.

The computer is doing this a couple times a day, so Id like to get it to stop

 

[400hp93talon]

Could it possibly be the cas is not at the right degree and the timing is advanced so its picking up spark knock and that would throw it into limp mode also. Just an idea.

That is most likely not the problem because the ecu would instantly pick that up I would think and it would come on again instantly after you cycle the key. But you never know.

 

[asb2106]

Could it possibly be the cas is not at the right degree and the timing is advanced so its picking up spark knock and that would throw it into limp mode also. Just an idea.

That is most likely not the problem because the ecu would instantly pick that up I would think and it would come on again instantly after you cycle the key. But you never know.

When i was looking it over last night I was wondering the same thing.

The CAS is flat, I lined it up with the tab on the CAS and installed straight in. No adjustments yet.

Should I advance or retard that any to see if it helps? Ive used the 95-96 CAS up till now, so this is my first on that side of the head.

 

[400hp93talon]

I would retard the timing first if that doesnt help any that most likely isnt the problem. You need to barely turn it counter clock wise to retard it if Im not mistaken.

 

[DSMer541]

I'm pretty sure the higher the number the richer and the lower the leaner.

no he was right....the lower the richer and the higher the leaner....look at your widand, it should say lean-stoich-rich (20-14.7-10) .........iv had this problem too but not as bad, and i have a 1g..... ill be cruising and all of a suden my wideband will jump from about high 14's to high 15's ...but as sooon as i give it gas it goes back down..... never figured out a problem....i think it has something to do with the ecu, might be caused from lots of little things like a exaust leak, or a bad sensor somewere or timing....

 

[400hp93talon]

no he was right....the lower the richer and the higher the leaner....look at your widand, it should say lean-stoich-rich (20-14.7-10) .........iv had this problem too but not as bad, and i have a 1g..... ill be cruising and all of a suden my wideband will jump from about high 14's to high 15's ...but as sooon as i give it gas it goes back down..... never figured out a problem....i think it has something to do with the ecu, might be caused from lots of little things like a exaust leak, or a bad sensor somewere or timing....

Well my aem wideband must be screwed up then because when my coil for 1 and 4 went bad all the unburnt fuel was goin threw the exhaust and the wideband was at 17+ then I got a new coil and it was staying 12.9 to 13s?????

 

[asb2106]

no he was right....the lower the richer and the higher the leaner....look at your widand, it should say lean-stoich-rich (20-14.7-10) .........iv had this problem too but not as bad, and i have a 1g..... ill be cruising and all of a suden my wideband will jump from about high 14's to high 15's ...but as sooon as i give it gas it goes back down..... never figured out a problem....i think it has something to do with the ecu, might be caused from lots of little things like a exaust leak, or a bad sensor somewere or timing....

yah im sorry, i read that wrong, thats correct. my wideband actually says the words rich and lean if it gets to the extremes.

My tsi never used to do this till the 6 bolt, but now at idle/coasting its going up in the 15s, goes back down under gas. Just concerns me alittle that its doing it. Im thinking its something to do with the CAS.

 

[400hp93talon]

My tsi never used to do this till the 6 bolt, but now at idle/coasting its going up in the 15s, goes back down under gas. Just concerns me alittle that its doing it. Im thinking its something to do with the CAS.[/QUOTE]

It's always(90% of the time) going to read leaner at an Idle than when it's under a load thats normal.

 

[asb2106]

It's always(90% of the time) going to read leaner at an Idle than when it's under a load thats normal.

sure sure, but I mean compared to when i had the 7 bolt short block with the 95-96 CAS. It would always run 14.7 or a little richer at idle. Only time I ever seen leaned out conditions were while decel. which is normal.

Now with the 1g CAS the wideband is all over the place. 14.0 - 15.6 during idle.

Its just new for me. It sounds fairly regular, just not what I was used to seeing.

 

[400hp93talon]

I researched some wideband informtion a bit ago and found the reason why mine was reading lean..when there is less air volume running through the sensor it automaticaly goes lean(during missfires)...so I apologize for putting false info in this thread!

 

[beniger]

i just read through and saw a bunch of wild info. Widebands go from lean 8. to about 18. 18 being lean and the other way being rich. If your going to play with the cas, you have to ground the jumper and watch the harmonic balancer with a light gun to know what you're doing to your timing. When you say accel do you mean getting into boost or just normal driving all in the vacuum range? Now to the lean what exactly are you doing when it goes lean, can you log? Does it doing under the same conditions?

 

[dunsunIII]

I know this thread is a bit old, but I would like to know what happen??? I was having the same problem with my last dsm after doing a six bolt swap. it would do this when I was just driving normal...but it never did this under boost..to fix this I got my ecu chipped. now I have an awd tsi and after putting on a 1g cas it is doing this again and I would like to know if there is any other way to fix this without getting my ecu chipped?? thanks

 

[asb2106]

I know this thread is a bit old, but I would like to know what happen??? I was having the same problem with my last dsm after doing a six bolt swap. it would do this when I was just driving normal...but it never did this under boost..to fix this I got my ecu chipped. now I have an awd tsi and after putting on a 1g cas it is doing this again and I would like to know if there is any other way to fix this without getting my ecu chipped?? thanks

Yah theres a fix...

I dont know if its the "right" way, but it has held up on mine, and I got the info from Magnus..

Quoted from Magnus 1g in 2g write up

So let’s get started, Parts needed:
· A 10K potentiometer (although a 5K would probably do just fine). These are available at any
electronics store, if you go to Radio Shack ask for a volume control knob because they don’t know
what a potentiometer is.
· Wire strippers
· Soldering iron
Step 1: Remove the access panel on the driver’s side of the center console. You should now see four plugs
with a ton of wires going to them.
Step 2: Pull out the top plug, it’ll be the one that’s the hardest to reach. Locate wire #85. It’s orange with a
white stripe.
Step 3: Cut the orange wire in half. Solder one end of the wire to the center peg of your potentiometer.
Solder the other end to either the left or right leg, it doesn’t matter which. Turn your potentiometer all the
way counter-clockwise.
Step 4: Plug the harness back in and start up the car. It should sound like it did before you did any
modifications. If the idle is choppy or the car won’t run you turned your potentiometer the wrong way.
Step 5: Add resistance to the barometric pressure sensor by slowly turning the knob on the potentiometer.
Drive the car

 

[rimmbrme]

start with the simple checks first, fuel, ignition, compression etc. and do a complete visual inspection. helps me a lot when diagnosing cars.

 

[dunsunIII]

ok cool man thanks I'll try this out...I don't like cutting wires but I hate how the car runs when I'm not boosting..I asked alot of other dsm peeps and they don't know what time talking about I think most peeps with a 6 bolt swap get link or do something to there ecu so they never notice this

start with the simple checks first, fuel, ignition, compression etc. and do a complete visual inspection. helps me a lot when diagnosing cars.

thanks Iv done all that..it is the cas... I broke the one on the right side, so I put on a 1g cas..had the same problem on my last car and the way I fixed that was the key driver chip from dsmchips.com

 

[asb2106]

its doing it because it is detecting ghost knock.

The potentiometer takes the sensor out of its range, it still detects knock and adjusts timing, it just wont send the ECU into limp mode like that.

other people have said using a blacktop CAS will eliminate that as well

 

[Tanro]

Running DSM Link is another easy way to fix this. Albeit more expensive. DSM Link has a checkbox to ignore RM codes.