Help needed - Surging under full throttle

[chilla]

Hey guys,

Strongly considering buying a tidy '03 TD5 S with 200K KM. Full log book servicing and drives well.
The only thing holding me back is under full throttle, the motor starts surging. It idles smooth and drives sweetly under normal operation. However, when you put the pedal to the metal, the revs start surging back and forth by maybe 300RPM or so. Doesn't seem to matter what speed your doing, but it definitely did it at 60km/hr and 95km/hr.
It's at a car yard and I told him to have his mechanic check the injector harness for an oil leak into the ECU. All clean there. Then I mentioned the previous owner may have adjusted the wastegate and it could be hitting overboost (all knowledge gained from this forum, so thanks to everyone for that). Can't remember if he said the mechanic looked for adjustment there or not. The mechanic's first thought was MAF sensor, so he checked that and reported back all good.
The car really is quite tidy apart from a few interior issues (drink holders stuck in, seatbelt pillar plastic cracked etc) but I can't bring myself to purchase it without having this problem resolved. But it seems like if they can't find the problem, they won't bother fixing it. So I'm really hoping for someone to give me some possible solutions.
I'd love to be joining the club of disco owners, but need to get this one nutted out first.
Cheers in advance for any suggestions. Have a good weekend.

[chilla]

Also, the EGR has been blocked off, not sure if that has any relation to a surging problem. Just thought I'd mention it anyway.

[Outback 1]

i had the same issue with my car it went away when the fuel pump failed and I replaced it with a new vdo unit

[scarry]

Raplacing the MAF fixed mine,it was surging only at full throttle.

[discorevy]

If the mechanic has the means to test the air flow meter then he should be able to read if the turbo is over boosting ( which is what it sounds like) , get him / her to put the hose from the intercooler pipe straight to the wastegate actuator , bypassing the modulator ( square thing with three hoses bolted near the bottom of the air con compressor), if the problem goes away get them to replace it, egr block off is fine.

[wardy1]

I'd back in the MAF. Less than $250 and 10 minutes to replace

[chilla]

I'd back in the MAF. Less than $250 and 10 minutes to replace
Well I've taken a punt and bought the car, so I hope you're right!

[discorevy]

I'd back in the MAF. Less than $250 and 10 minutes to replace

Disconnect maf to diagnose , free and 2 seconds to do :D,
If you need a boost modulator its about $65 and 10 minutes
Would recommended a nanocom .... Worthy investment
Enjoy your disco, auto or manual?

[wardy1]

Well I've taken a punt and bought the car, so I hope you're right!
Enjoy!
I got my replacement MAF from someone in Brisbane... in Red Hill? Send a message to Blknight, he'll be able to help you out.

[chilla]

Disconnect maf to diagnose , free and 2 seconds to do :D,
If you need a boost modulator its about $65 and 10 minutes
Would recommended a nanocom .... Worthy investment
Enjoy your disco, auto or manual?
just d/c and take it for a drive?? Wouldnt that cause all sortsa funky crap?

[discorevy]

No , it defaults to preset parameters in the ecu , which will allow diagnosis , and let you drive it until you get a new Maf ( if it is that ) . it won't affect it like disconnecting a petrol one. Ultimately you might want to get a nanocom , for now someone might be kind enough to plug in and diagnose it for you if they life close by

[chilla]

Ok. So pretty much what you're saying is, when the MAF sensor is d/c, the ECU will run of a default setting. Therefore if it the car doesn't surge when the MAF is d/c, it points to it being faulty?

[wardy1]

No funky crap, but its not definitive either.
Pretty sure someone here will be happy to lend or help with a nanocom but honestly, a PM to Blknight could make you feel better.
IF you decide to disconnect the MAF, LISTEN!
Surging will probably be worse but maybe not.
Major signs with MAF still connected:
BIG flat spot at 110km. Read NO acceleration.
General lethargy from 80km
These are just a couple of symptoms.
good luck

[sierrafery]

Ok. So pretty much what you're saying is, when the MAF sensor is d/c, the ECU will run of a default setting. Therefore if it the car doesn't surge when the MAF is d/c, it points to it being faulty?
In a nutshell: yes, just that it will have a slight hesitation on take off and if only the MAF was the problem of the symptom it will run well, and check fuse F2 engine bay to be ruled out

[discorevy]

Ok. So pretty much what you're saying is, when the MAF sensor is d/c, the ECU will run of a default setting. Therefore if it the car doesn't surge when the MAF is d/c, it points to it being faulty?

That's pretty much it , but a trip round to bsperkas to look at live readings will clarify, maf reading if good will be around 55 - 60 at idle through to 600+ at full noise , over boost surging will happen at 1.4 bar and above.

[chilla]

So hooked it up to a nanocom and maf seems to be working alright. We couldn't check boost settings. However, on the way home, it no longer surges. Instead, everytime i go full throttle, the revs stay the same and so does speed. If i back off completely and then accelerate smoothly, rpm and speed pick up. As soon as I go full throttle, rpm stays still as does speed...

[sierrafery]

If no faults logged it seems very like fuel pump HP failure, it can run on LP without power

[chilla]

If no faults logged it seems very like fuel pump HP failure, it can run on LP without power
I forgot to mention, faults were:

"03-05
Accelerator Problem 1
CURRENT"

"pump failure 1 (monitor line)"

"CODE P1884
CAN MESSAGE MD_IND INVALID
(FLAG F_TL_MES)"

[sierrafery]

So check live readings on throttle sensor way 1 , you should get track 1 + track 2 = supply all the time, can you hear the pump running?

[chilla]

So check live readings on throttle sensor way 1 , you should get track 1 + track 2 = supply all the time, can you hear the pump running?
Yeah I can hear the pump run for about 5 seconds after I turn ignition on (from somewhere at the rear of car)

[chilla]

Sorted. Bypassed modulator and we're running sweet. Off to Double Island it is!

[chilla]

Thanks to everyone for their suggestions and help. Legends.

[sierrafery]

It's something strange then cos you should have got overboost fault code for that

[chilla]

Yea i found out after I posted, that 20-02 turbo overboosting fault was logged.

[wardy1]

Glad it seems to be sorted. I think you've quickly learned the huge value of this site!

[chilla]

Yeah I used to own an S2000. Obviously those cars are a lot more rare and unique than a discovery, but the S2K forum is very similar to this. Full of enthusiasts very willing to lend their time and help each other out. We used to have some awesome meet ups, hope to see the same thing happening here. Cheers again.