Overboost issue

Really hope someone can help me. I have a Discovery 2 2003 (70k Miles). Ever since I had a remap from Mike at Dynachip i have had an issue with what I think is overboost.

Dynachip are professionals and do hundreds of discovery remaps a year so I’m confident it’s not the remap. It also doesn’t happen all the time. I can drive for an hour sometimes and it will drive fine. At other times it does it from the start.

At around 3500 rpm on full throttle, the engine feels like it is misfiring. Behaved like when you hit a rev limiter. If you ease of the gas the car changes up and off you go. If you keep your foot down it will eventually continue to rev and then change gear. Shortly after this the M and S light will flash on the dash as will the D on the gear box. It goes into limp mode. If you turn the engine off and on it clears and drives fine until the next occurrence which could be straight away or not at all that day.

Most of the time it throws no fault codes. The other day it threw an ‘airflow circuit fault logged high’.

The car only does 3000 miles a year max so isn’t used daily. I have found other threads that appear to be talking about the same issue but I have tried the various suggest remedies to no avail.

• Xyz switch was done under warranty by the garage I bought it from. Made no difference
• Replaced wastegate modulator. Made no difference
• Checked ecu red plug for oil. Clean as a whistle.
• Checked wastegate was freely moving and not sticking.
• Replaced MAF sensor. Made no difference.

Getting expensive changing parts for no benefit. I have read that I should change transmission oil and filter however this is another few hundred quid and this feels to me to be an overboost issue.

Does anyone have any suggestions that could be of help?

Thanks

Matt

I also have a Dynachip upgrade & know he usually runs his diagnostic machine on the car before he installs the upgrade - so would normally spot any faulty compts. However, he is very experienced & has probably seen many issues previously From my experience I know he is very helpful when a customer has a problem . Have you contacted Mike & explained your symptoms & asked for his thoughts?

Yes you are right he is very thorough. I had no faults and he checked over things like oil in the red plug etc. He thought it was an xyz issue which is the first thing I have replaced.

Im certain it’s an overboost problem. Just found another thread on here where the chap had the same issue and couldn’t solve it having tried everything possible.

Going to check all hoses for pin holes and blockages and re check wastegate movement

Do you have diagnostic that allows you to watch live data.
If so drive it to trigger fault whilst watching what mass air flow reading is, if it gets to 650 it triggers limp mode,
To rectify you would need the remap fuelling down a little or fitting a maf clamp,

johnlad said:

Do you have diagnostic that allows you to watch live data.
If so drive it to trigger fault whilst watching what mass air flow reading is, if it gets to 650 it triggers limp mode,
To rectify you would need the remap fuelling down a little or fitting a maf clamp,

Click to expand...

Or run with maf disconnected

Mine done similar, my tuner told me when in 3rd gear (manual) and pulling up a hill the boost should be between 1.30-1.35. Mine was hitting 1.42 sometimes, wound the waste gate rod back a half turn and brought the boost back to 1.35 and no more issues. I take it that it feels like you've suddenly hit a limit and it almost jerks and backs off? Mine also logged the same code.

We ran some live diagnostics the other night but sods law it drove perfectly the whole time. Last two days its done its kangaroo impression within the first half a mile but after the initial mile it is fine.
MAF has been replaced but i will unplug it and see if it makes a difference.
Next on my list is to play around with the wastegate just to be certain it isn't sticking. If that doesn't help ill wind the wastegate rod back half a turn.
Thanks for you suggestions guys.

I had a dynachip remap. He was a bit enthusiastic with the wastegate rod - it was fine for his testing but the first big hill it hit overboost. Just needed lengthening a bit. But you would need to see what the manifold pressure is actually getting to first to confirm. Also if mass air flow goes over 680kg/hr this will cause the high air flow fault.

Hi, I had a similar issue with mine after a remap 2 years ago. It was fine for 9 months and went like a rocket through the rev range. It then started misfiring like yours and eventually was diagnosed as overboosting and the MAF sensor triggering limp mode. Around the same time the remap was done I also did an EGR bypass and over the followihg months the engine has cleaned itself up and power has gone up, causing other systems to overload. The solution was to remap again with a less powerful map and that's cured the problem. Good luck