What causes a motronic 16v to run lean at WOT?

[greatfox]

I'm trying to troubleshoot my lean running engine. My air fuel ratio is about 14:1 at 4500 RPM and goes up to 14.5:1 at 7k RPM. I've got a techtonics chip so I would expect my car to have EXTRA fuel, not less than normal

So what are the common causes of lean running motronic 16vs at WOT? Any help would be appreciated

[antichristonwheels]

vaccum leaks

bad grounds

trash in system

[greatfox]

Quote, originally posted by antichristonwheels »

vaccum leaks bad grounds trash in system

Don't have bad grounds, I don't THINK I have vacuum leaks.....where are the common places for vacuum leaks?

And what is trash in the system?

[kalamos23]

Not sure if this will help, but is your timing correct? Mine was running really lean as well and we advanced the dist. a bit and it seemed to help, especially in the lower gears. We'll see tomorrow as I make the drive to work. I also noticed my oil temp was running abnormally hot (100-110 cel. vs 80 cel. normally). My temp went down and I got a lot more acceleration after turning the dizzy a bit.

[greatfox]

Quote, originally posted by kalamos23 »

Not sure if this will help, but is your timing correct? Mine was running really lean as well and we advanced the dist. a bit and it seemed to help, especially in the lower gears. We'll see tomorrow as I make the drive to work. I also noticed my oil temp was running abnormally hot (100-110 cel. vs 80 cel. normally). My temp went down and I got a lot more acceleration after turning the dizzy a bit.

I appreciate the help! My timing was played around with by the guys at DRS. They tried advancing it and retarding it but that wasn't the problem. My oil temp sits at about 202 Fahrenheit when at a stoplight and about 195 when driving

[greatfox]

bump for help. What sensors should I replace to eliminate them as potential causes of the problem?

When WOT is engaged, the system is in closed loop yes? So what is controlling the amount of fuel the engine gets? Is it just the ECU? Do I just need a chip reburn from TT (I already have a TT chip)?

Please help me out!

[bzflag]

make sure your full throttle switch on the tbody is working correctly. That switch richens the mixture.

[greatfox]

I'm pretty sure the WOT switch works, is there anything else that could be the cause? My car runs perfectly, starts everytime first time, and has just had a tune up recently...

[Scuba2001]

Check the resistance on the switches.

[greatfox]

Ok, so once my car was warmed up, I opened the hood and revved the engine up past 4k rpms and slowly let it down just before it reached the closed throttle switch (it didn't activate it). Then with my other hand I pressed the WOT switch to see if it would bog a little with the richened mixture and it didn't do anything

Is my WOT switch bad, or is my little unscientific test bogus??

[Scuba2001]

Quote, originally posted by greatfox »

Is my WOT switch bad, or is my little unscientific test bogus??

If the car didnt bog down at all, or change pitch, I would say that the WOT switch is gone out the window. I might have a spare sitting around, if youre interested.

[bzflag]

Check the WOT switch with a multimeter. I don't have my bently in front of me but there is a test specified in the bently for the WOT switch.

[greatfox]

I'll do that this weekend. If it isn't the switch, is there anything else I should check?

[redGTInj]

bump for some MORE info on this

[armymech666]

I just checked my WOT switch the other day. I activated it at idle and nothing happened. I tested it for continuity and it worked fine. So, I am guessing that maybe the wiring going to the ecu is bad. I just haven't been motivated to test any farther yet.

['88Jetta16v]

To get full throttle enrichment, the car must be ABOVE 2500 RPM with the switch activated. If you're testing the switch below 2500 RPM, it will seem that the full throttle switch is bad, even if it isn't.

[redGTInj]

good to see guys still helpin out...

last night i had a chance to extend the wiring for my test harness so i could put my meter inside the car while driving...

needless to say everything was looking good..very high reading at cold start numbers come down gradually at idle 2.5ma avg numbers bouncing around properly...

EXCEPT while cruing with lite throttle input on highway say 75mph meter was reading 12.6ma not budging...

THEN with WOT in any gear the numbers did NOT jump up...as they should car currently has AMS chip

['88Jetta16v]

Great idea to extend the test harness, I should do that myself.

But your numbers should have jumped for certain above 2500 RPM at WOT. I believe the factory enrichment is 19.x mA. On my old GLI, with the Autotech module turned to the highest setting (Jetronic not Motronic, of course), I would see about 26 mA if I remember right.

[redGTInj]

yea having it in the car whiel driving is perfect for diagnosing..

yea with a module thats about right... my other car "the beast" i had a homemade module that was adjustable and on the dyno it made 177WHP and dpr reading would soot up to 35ma!
fun car!

although i never tried this test on a motronic car.....i would assume teh reading shoudl still jump up dramatically.....

im gonna check the black and blue wire (full throttle switch) back to the ecm..

[redGTInj]

after work bump

[redGTInj]

bed bump

[redGTInj]

no change in dpr current at WOT still

[Viveka]

Back to Basics

The most common problem when FI goes lean at high RPMS??

Check fuel pressure AND fuel volume @ the same RPMs you are going lean.


if its not to spec. , do not immediately condemn the pump.

Go through the diagnostics (could be filter ,lines, relay...)

[redGTInj]

thanx for the reply...
everything is working correctly..EXCEPT for the current changing at full throttle... stock should jump to 16ma

this has TT chip, so i would assume based on other chips etc..around 20ma would be probable..

my concern is that even while cruising i get 12.6ma with part throttle and does not change until decel, or at idle..

tested switch at the ecm and switch is good...

so im leaning toward sthe fuel dizzy itslef..as teh system is motronic, but is using a KE-jetronic fuel dizzy, with WHITE DPR..instead of black...

[redGTInj]

im havin this problem

[ellocolindo]

i am not a ke-jetronic or mk2 person. i have had and worked on passat motronic cars only.
but your problem i think it lays in the fact that the motronic DPr has to be black and a certain part number.
i have seen people lookign for replacement DPr 's before and they were told to match up the number and color on the parts.
there are differences.

that could explain the cituation; the WOT switch works; send the signal tot he ecu; the ecu sends the signal to the DPR; but the DPr is the incorrect and does not respond to the ecu output...

[ziddey]

there's no differentiation between wot signal and regular signal. the fact that a higher current is sent through the dpr in open loop when closed means it works as it should.

i'm really curious if the op solved the problem, especially since the wot signal is reaching the ecu. has a different ecu been tried? i know for the earlier cis-e + knock box, both modules receive the wot signal. maybe it's not getting to the fuel side of the motronic ecu somehow.

[redGTInj]

im havn this problem on a motronic 16v in a 83 rabbit...on teh dyno air/fuel was 16:1 after 5,000 rpms!