C70 surging RESOLVED, bad off brand MAF

kwma01 · Post by **kwma01** » 19 Jul 2013, 09:31

I am having a problem with my 1999 C70 2.4L Turbo. The car tends to pulse or surge when it is put under a load for a few seconds such as when you go up a long hill. It is very noticeable as the engine revs between 2000 & 2500 rpms repeatedly.
I have the CEL illuminated and am getting 3 codes.
• ECM-430D (Minor Vacuum Leak)
• ECM-6806 (Turbo Charger Control System flow fault – Flow too high)
• ECM 260A (Long term Fuel trim bank 1 – Lower limit)
I have removed and cleaned the ETM. I have bypassed the TCV by connecting the boost line directly to the waste gate valve. Neither of these has corrected the problem. I have smoke tested the intake system without any noticeable leaks. I had to replace the MAF about a year ago and I have ordered new hoses for the Turbo Control valve (Should be in next week).
I have a Dice scanner and was able to capture a few images of the occurrence. It is clear that the TCV (black line), Turbo pressure (blue line), and MAF (green line) are showing the pulsations. In the second figure the throttle position is very flat so I do not think it is an ETM issue. The first image has the TCV connected and the second one has it bypassed. Does anyone have any ideas what to look at to solve this issue?

I would appreciate your suggestions.

Post by **jimmy57** » 19 Jul 2013, 10:19

First check would be wastegate acutator. The scale of graphs is wide enough that I can't tell what pressure it is actually boosting but a cracked wastegate actuator diaphragm can open when it gets to a certain pressure and cause boost fluctuations when TCV is OK.

Post by **JimBee** » 19 Jul 2013, 10:35

"Under a load" suggests increased engine temperature. Might temp sensor (in the t-stat housing) be failing? I'm not sure what its signal does—adjust the timing? make the fuel-air mix richer? If it did the latter then the O2 sensor might notice the fuel is too rich and send back a signal to make it leaner? or trigger the CEL?

Can someone affirm or refute this guess?

Post by **jimmy57** » 19 Jul 2013, 11:59

On late models the ECT signal is well monitored and if it doesn't track correctly after engine starts there is a code that points to thermostat or ect sensor.

The issue seen on the graph is there is an airflow oscillation. The boost oscillates, the MAF signal oscillates and the TCV signal is ramped up to try to dump boost but boost doesn't come down.

The codes may all be the result of the boost oscillations.
The diaphragm in wastegate actuator could be the small vac leak. The MAF signal being erratic could be the fuel trim code cause. The fuel trim code is for lower limit which means it was rich and the fuel trim was lowered 25% to try to fix and at 25% it flags code.

kwma01 · Post by **kwma01** » 19 Jul 2013, 12:23

Thanks for the ideas. i will start by pressure testing the actuator and let you know what I see.
Wade

kwma01 · Post by **kwma01** » 19 Jul 2013, 21:42

I checked the waste gate actuator and it seems to work fine. I then hooked up a pressure gauge to the red pressure line from the turbo and did not get any pressure while reving the motor from idle up to about 3000 rpms. Maybe the boost line has just become disconnected. I will try to get under the car this weekend and see what is happening.

Post by **jimmy57** » 19 Jul 2013, 21:50

That does make sense. The direct connection had no effect because it changed nothing.
The oscillations may be the ECM overboost protection cycling

kwma01 · Post by **kwma01** » 20 Jul 2013, 16:20

I was able to jack the car up today and crawl under it to look at the boost pressure line. It was connected and looked good. I then took a blow gun and blew out the hose. It did not seem to have a blockage. I hooked up the pressure gage and started the car again. I reved the engine quite a bit higher than I did yesterday and I saw the boost start to kick in. I was still only getting 2 psi at about 4000 rpms. This seems pretty low to me. Can you give me an idea of the normal boost that I should see? What else could it be? Waste gate or bypass valve?? BTW the bypass valve does hold vacuum.

All help is appreciated.

Post by **jimmy57** » 20 Jul 2013, 16:28

The boost pressure is load dependent. Revving an engine doesn't produce much boost.
Check the line from TCV to the wastegate for leaks

kwma01 · Post by **kwma01** » 21 Jul 2013, 09:48

The line to the wastegate holds a vacuum so I would say that it is fine.

I noticed the problem shortly after removing and cleaning the ETM. The TPS shows that it is not pulsing however I wonder if there is something else that may cause the pulse from the ETM. Does anyone know of a test to confirm the pulsing issues with ETM's?

I will continue to fix the turbo but I do not think this is the source of the pulsing any longer.

Thanks
Wade