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I have a vw vr6 24v engine that is slow too enrich on WOT acceleration. After logging with my wideband sensor, it can take 3 seconds in 3rd gear before enrichement finally settle down to acceptable levels. I reach 18 -19 AFR during the first 3 second of acceleration. The AFR will finally dip down to 12 and wil thenl slowly rise to 13.5 at 7000rpm. What could cause this slow enrichment upon initial acceleration ? It’s causing the engine to knock, the ecu will pull timing and the knock will get to lower level as RPM rise.
Under normal driving if I accelerate and hit over 30% load I also get the knocking problem. Rising octane of the fuel won’t change the behaviour. I do not have any codes stored in the ECU for this issue.
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a lean condition can be caused buy a maltitude of things, low fuel pressure for example, a fuel leak, o2 sensors not sending correct data to the ECU to adjust air fuel mixture… kind of strange you aren’t getting a engine light. even a vacuum leak can cause a lean condition.
I think you need Scanner Danner on this one. I’m wondering if the MAF is dirty or the duct work is leaking….??
Looking at the lambda of the ECU. It doesn’t look like the the ECU see the lean spot the wideband does. It’s the same type of wideband sensor that is used by the ECU and my Wideband. I’ll reverse the sensor tomorow and log again they have the same type of connector.
I don’t know VW’s but on Fords and GM the PCM (ECU) will ignore a borderline MAF input if the TPS is correct. They figure the “fast talking system” will correct until you have a hard failure. I would ask VW and see if a reflash is available.
If you could video your test… that be something to see and learn by!!!
Are you talking about pre-ignition rattle? If so, my first suspect would be an EGR system fault followed by a knock sensor.
After reading your post again I missed wideband sensor and I guess the 02 sensor(s) are Bosch Wideband Air/Fuel ratio sensors?
What type of a Wideband Lambda tool are you using for data?
Ok you stated “it looks like the ECU doesn’t see the lean spot but the Lambda does” I would verify that by looking at the pulse width MS of the injectors and verify. If you don’t have an immediate reaction from TPS to injector pulse width with no SES light I would be looking at an ECU or a reflash of the ECU. If the injectors are reacting to specs and fuel pressure is to specs maybe look at the variable intake manifold door operation. GM had a big problem with the door actuator not working/hanging up which cause pre-ignition and drivability issues.
Another thing that just came to me… if the vehicle has Wideband Air/Fuel ratio sensors they should be picking up that lean spot….another ECU error…
I wish I could help more I’m just an old wore out Chevy / Ford Tech.
[quote=”Bluesnut” post=146217]Are you talking about pre-ignition rattle? If so, my first suspect would be an EGR system fault followed by a knock sensor.[/quote]
Yes, Knock sensor were retorqued to spec. There a 2 knock sensors on this engine one for cyl 1-3 and the other one for 4-6. The ECU is seeing knock on all cylinders. The ECU is pulling a lot of timing.
Issue as not been found yet. Currently leaning toward a possible TPS or MAF issue. Running with MAF disconnected doesn’t solve the issue. The MAF does reach acceptable maximum value.
The TPS is part of the throttle body and the throttle body needs to be replaced if the issue is the TPS.
I Just want to repeat my self ECU as no codes stored related to this issue.
Yes I’m using LSU 4.2 Bosh wideband sensors. Wideband tool is an Innovate LM2. I believe the resolution on the LM2 is a lot higher.
I’m now using lm2 wideband sensor for the car ecu and car sensor for the LM2. There’s no changes in behavior.
I pressurized the intake manifold and didn’t find any leak.
JTF you are saying I should log TPS and injector pulse width (ms) ? If so I beleive I already have a log file for this. I’ll take a look at to see if pulse width increase immediatly when touching the gas pedal. If I don’t find the data I’m looking for I’ll make a new log file.
FYI this car as drive by wire gas pedal.
madonion stated:
JTF you are saying I should log TPS and injector pulse width (ms) ? If so I beleive I already have a log file for this. I’ll take a look at to see if pulse width increase immediatly when touchingI wish I knew VW’s, but in my own layman’s words I’ll try to explain what I was saying….If a VW person gets on here and says “I’m full of it” please understand I’m a old Ford/GM tech and don’t really know nothing else….
First- If you can log the TPS, injector pulse width, O2, MAF, AFR and knock sensor data during the first 3 second of acceleration. Can you snap shot the data? Second- Than do the same after the enrichment settles to acceptable levels {13.5-14.5} (snap shot the data). Third-Under normal driving at/over 30% load log the same data (snap shot the data).
What you need to look at if the sensors are reading correctly and the ECU is adjusting accordingly. To do this you need the Performance Information Data (PID) for your car. I don’t know if you can find this in the internet or if VW will give it to you.
In general if the TPS data shows full throttle and injectors are not at the full duty cycle the ECU is not telling them to do so or something is telling the ECU not to. For example any sensor that is not giving the ECU the correct information that has been preprogrammed with the Performance Information Data for your car.
I had something very similar one time on a Cadillac Northstar under normal driving at 65 mph highway slight incline engine slight ping. It was found the PCM calibration was to lean after the engine was broke in. GM programmed the PCM after 5K miles (engine break in period) to start running leaner. They did this by reducing pulse width modulation via fuel injectors at certain PID’s preprogrammed. The fix was recalibrations’.
One other thing…I don’t know if VW is set up like Ford and GM, but when you disconnect the MAF a Map sensor will take the place of the MAF and a SES (MIL) light will come on so, what you may be seeing is programmed MAP sensor readings to keep the engine running.
Wish I could help more…
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