Thread: 2004 Discovery 2 TD5 overboosting at high RPM

How old was your MAF when it starting given bad values?

Dunno , it was like hat when I bought it. Probably original!

I doubt whether POs had ever seen full revs.

While driving home the car stopped with all dash lights on after PO had paid a mechanic something like $400 to fix problem. Problem was stated as power steering got heavy as it does with the engine stopped!

One new battery terminal later all was fine except the alternator died soon afterwards.
Regards PhilipA

Originally Posted by Young1

Yes i you are correct. i think the low boost reading are a side affect of a conservative (14 threads) on the waste-gate modulator to limit the surging symptoms.

I am more interested in the MAF readings.

• sitting at 68 g/s while idling
• moving to 600+ g/s while hard acceleration.

This indicated to me that the MAF is functions, but giving HIGH values throughout the range.

Is there something that can cause the MAF to do this, or is it just a symptom of a fautly sensor?

Read again post #13, seems that your MAF is reading high from the beginning cos it should be around 55 at idle and at 600 the boost should be at max level, as it's low the managment wants to increase it so the sucction gets higher that's another side effect... as i said with 14 threads on the wastegate you just make this worst

Originally Posted by sierrafery

Read again post #13, seems that your MAF is reading high from the beginning cos it should be around 55 at idle and at 600 the boost should be at max level, as it's low the management wants to increase it so the suction gets higher that's another side effect... as i said with 14 threads on the wastegate you just make this worst

Still no luck with this.

I have replaced with a new MAF (OEM one) and symptoms have gotten even worse.
The car struggles to rev past 2500 rpm when stationary in P. It will go higher just struggles.

When driving, it will not rev past 2200 rpm, under slow acceleration OR fast acceleration.
This is independent of the waste gate actuator threads (I tried from 14 threads to 10 threads with the same results).

Really doing my head in this car, everything i check/change/replace is it PERFECT condition and yet the problem persists. I would love to be able to drive my car.

Did you measure the boost with wastegate at 10 threads? cos if it doesnt got higher it can be a turbo fault too... provided you are 100% sure there's no boost leak, you should do somehow to pressure test it.... and btw, OEM MAF is just a branded aftermarket, usually those VDO units which failed the tests imposed by LR to become genuine but still ISO compliant within a wider accepted reading range... it's possible that in your case not the sensor is the problem but it can be ruled out only with genuine LR(i know it's expensive but it's the only 100% reliable) Drive it with MAF unplugged untill you find the culprit to be able to fix it for good.

Another relevant test would be to clamp the hose which goes to the wastegate valve and make a drive test that way with MAF unplugged ... if the boost side is OK it should go to overboost below 3000rpm, if it doesnt the problem is on the boost side or the MAP sensor is reading low. This is an ugly fault and needs lots of tests

Hayden,
Happy to go for another drive with you with the Nanocom to test the new MAF. Just drop me a SMS.
Chris

Originally Posted by sierrafery

Did you measure the boost with wastegate at 10 threads? cos if it doesnt got higher it can be a turbo fault too... provided you are 100% sure there's no boost leak, you should do somehow to pressure test it.... and btw, OEM MAF is just a branded aftermarket, usually those VDO units which failed the tests imposed by LR to become genuine but still ISO compliant within a wider accepted reading range... it's possible that in your case not the sensor is the problem but it can be ruled out only with genuine LR(i know it's expensive but it's the only 100% reliable) Drive it with MAF unplugged untill you find the culprit to be able to fix it for good.

Another relevant test would be to clamp the hose which goes to the wastegate valve and make a drive test that way with MAF unplugged ... if the boost side is OK it should go to overboost below 3000rpm, if it doesnt the problem is on the boost side or the MAP sensor is reading low. This is an ugly fault and needs lots of tests

Yes the new MAF is a VDO, always great to know the OEM part might not even work .

Yep i agree, i connected a boost gauge today and was reading max 14 PSI (measured at the inter-cooler intake pipe) with the MAF unplugged at any speed above 2200 rpm.
This was the same with or without the MAF plugged in.
Its seems like either the wastegate modulator is diverting pressure too-early/too-much or the is a boost leak in the system.

Doesn't make much sense to me how:

1. I drove to the mechanic (with presumably bad MAF unplugged) and the car was okay.
2. Literally only changed the MAF to a new one.
3. I drove home with new MAF and the car was not making enough boost.
4. I drove around with new MAF unplugged and the car was not making enough boost.

How can step 1 and step 4 yield different results? no variables have changed.

Anyway, i will test the to see if it overboosts without the wastegate modulator like you described on Saturday.

Originally Posted by cjc_td5

Hayden,
Happy to go for another drive with you with the Nanocom to test the new MAF. Just drop me a SMS.
Chris

Yep possibly may still be in need of your Nanocom assistance. Appreciate it.

How can step 1 and step 4 yield different results? no variables have changed.

It's possible to be an intermittent leak or sticking wastegate ... the worst scenario is to be some bad contact in one of the electric circuits... i don't remember, is the EGR bypassed ?