MAF Cut

[reb78]

I have posted this in more than one place, but I want to capture as many ideas as I can as I am still struggling to find a solution. Neil (V8Freak) and I have spent a fair bit of time troubleshooting this, but so far without any joy.

What are the reasons for 'MAF cut' on the Discovery TD5? By this, I mean at high revs under load, between 3750 and 4250rpm you get a cut that seems like a misfire that causes the engine to hesitate/kangaroo. Sometimes you can drive through it, sometimes it sticks there. The MAF reading on nanocom peaks and then goes to zero whilst it is doing this. Often, but not always, this fault code appears after this has happened: (3,7) AIR FLOW CIRCUIT, (LOGGED HIGH). More recently, have noticed the MAF zero at these revs but no kangarooing has occurred.

A friend and I have done a lot to try and resolve this but without success. I wont put it all here yet as i would like opinions without biasing them first!

There are lots of reports on this on many forums, but noone ever seems to post up a definitive solution!

Car is a 2004 manual EU3 TD5 16p and has been doing this on a standard map. EGR and CAT are removed. It did it with and without the CAT and the EGR has been removed the entire period of my ownership so cannot comment about whether it did it before EGR removal or not.

 

I am attaching an excel file with four nanocom logs for anyone that could shed light on it with info from them. The tabs at the bottom of the file give you the info, but I tried four things:

1. Standard car. MAF and wastegate modulator NOT bypassed - you get the MAF cut and you can see the MAF readings go to zero at that point
2. MAF Disconnected and modulator connected - No cut at high revs - MAF readings obviously always at zero because its disconnected!
3. MAF disconnect and modulator bypassed - No cut at high revs (probably because the MAF is still disconnected)
4. MAF connected and modulator bypassed - there is a cut at high revs, BUT the MAF readings don't zero in this run

 

So far, we have tried (in no particular order):

1. New wastgate modulator - genuine part
2. Tried a brand new VDO MAF
3. Checked and tightened all intercooler hose connections and the inlet manifold
4. EGR and CAT removed
5. Brand New wastegate actuator fitted as well as trying one from another vehicle
6. Wastegate is free and able to move
7. I read somewhere that the CKP could be sending a dodgy signal, so have tried a known working CKP
8. Wastegate modulator hoses all replaced with silicon
9. Silicon intercooler hoses fitted
10. The original wastegate rod was set at 12 threads. I have tried 13 and it made no difference.
11. Intercooler removed and leak tested (this was using rubber gloves to seal the ends, so the pressure may not have been high enough to reveal a leak, but it looks pretty good and has virtually no oil in it)

TD5 Engine Runs.xlsx