ZD30 flat spot - no power

Hi guys, tried a search but nothing really jumped out at me....

I have a 2003 GUIII auto with 153k on it. It has the dawes setup, 3 inch Scott's Rods exhaust, EGR plate, auto fully rebuilt and nomad valve body. Serviced every 5 k and always use Delo 400.

Until a couple of months ago it was driven daily, a round trip of at least 70 km, but has since sat in the driveway, maybe doing a short trip to the shops once or twice a week. All mods have been in place for ages. I noticed the other day that it had a bit of a flat spot, really a hesitation when accelerating. Then yesterday, the same thing but much much worse, almost undriveable. It moves off ok, however any attempt to accelerate further just sends it down this deep hole and it almost dies. lift off the accelerator and it comes good again. It will build speed but very slowly. It is almost like it is hitting a rev limiter as it is quite a sudden drop.

I was thinking that the turbo, intercooler or associated pipework might be leaking boost, or in the case of the turbo, not producing any, but the fact that the boost gauge is indicating the levels of boost I have always experienced leads me away from that as being the culprit. I thought it may have been some dodgy fuel, however I always buy fuel at the local BP which has a pretty high turnover and I always run some chemtech diesel power in the juice, so I think I'll discount that. Also changed the fuel filter for no improvement.

Not being terribly experienced in diagnosing diesel issues, could you blokes provide some of your knowledge in pointing me to the components I should be checking to isolate the problem?

It's frustrating for me,if it was a petrol engine I'd have no problems in working out what's wrong, but diesels are relatively new to me and the only experience I have is through servicing it myself and avidly reading these forums regularly. I don't post regularly, but I do make comment when I can help someone out. I'm hoping someone may be able to help me out this time.

What is it boosting to, and have you cleaned the MAF sensor recently.
Sounds a bit like its going into limp mode??
Check all hoses for splits especially the blue one in the pic, it can blow off

You will need to remove the engine cover to check

Boosting to about 15 psi before the dawes drops it back to about twelve. MAF has been cleaned, might try pulling the intercooler off and cleaning inside, make sure the catch can is doing its job..........

You may have a large crack/leak in the IC if its still OE chances are its leaking/oily
, test it when its out not too much pressure though

A longer shot, but make sure all your sensors are plugged in properly.

Thanks threedogs, but if it was leaky, would I still be seeing 12-15 psi boost? I'm heading down the TPS path at the moment, as it seems to drop out both under load and when coasting and then accelerating. Sort of happens at a certain position of the right foot if you know what I mean. Have ordered an ECU TALK cable so I can do some real time testing, but its starting to drive me crazy.

TPS or maybe ECU relay .

Does it happen in any weather? Or only when its raining etc etc? I'd go over every hose and clamp real close first off. Sort of sounds like you have a slight boost leak and the leak is holding off to a certain pressure then letting go. But it could be anything, but boost leaks is the first port of call I reckon.

I had a similar prob on my zd30 gu11 turned out to b a head gasket

Wow! On a GU11? Well OP. Remove the cap, start her up and have a look see.

Thanks for the replies guys... HOpefully my ECU talk cable will arrive tomorrow and will point me towards a culprit. No matter what, I''m planning on ripping the intercooler and intake off on the weekend and cleaning the crap out of it all. My catch can is a one size fits all from Autobahn modified a bit and stuffed full of steel wool so might even need to go the full on provent route.

Couldn't resist, just had to go out and test out the head gasket theory. No tell tale signs though. At least that's one thing exonerated.

The only way I could tell it was the head gasket was to remove the head had a chunk missing size of a 10c coin from the head between cylinder 3 and 4 did a comp test but that didnt say much as I still had 250psi in each cyl and the other 2 had 300psi so engine was due for a rebuild anyways

OT but I have to laugh at myself when i go over posts I have written when I have had a few too many beers. Which is often... I read dirtygu's post as he had a GU11, as is eleven. Haha!!! GU11 as in 2. I've killed way too many brain cells lately...

Ok, ECUTalk cable arrived and it's hooked up and working. Should have got one of these years ago. It's showing fault code 46 which is intake air. The MAF voltage is showing as 2.77 volts at idle, rising to well over four on acceleration. Pulled the MAF and cleaned it but no change. What's the
opinions now - faulty MAF or something else?

Can you swap MAF with someone close by to try.
at least you can eliminate the MAF that way
You're a funny man mudski lol

Hey im interesred in the ecu talk. What do you actually need to use these things?

Only certain early gu use this system but
you'll need the OBD2 port which we all have

So do I just need the consult cable and use the available software and use a laptop? I do I need to get the primitive looking display?

I thought they were a small LCD display that you entered codes to receive values etc.
Give Pete an email he'll sort you out

There's two types: a USB dongle and one with a small screen.

I have the first one, and am looking for the second type with the screen.

MAF voltage at idle should be around 1.95-2.00 V usually.
Anything over 4.2 V at "incorrect" RPM will also in result limp mode.
This however is not necessarily faulty MAF but it could points to one, it could get misleading reading because extra resistance bad connection whatever or other issues. Are there any other codes for MAF?
Code 46 doesn't indicate MAF sensor as primary/foremost problem, possible causes are induction system, turbo, intercooler than MAF.
Cheers

The voltage is climbing with revs, and gets to nearly five volts (as near as I can tell watching the laptop and the road at the same time.) IT really is like flicking a switch - one minute fine with no indication of a problem, then straight down the big hole. Seems to usually be just over tow grand on the tach.....
There doesn't seems to be any leaks in the intercooler or its plumbing, I'm getting the same boost as I was before so I'm ruling out the turbo. What other 'induction system' components are there?

I think you've covered it all as far as induction components are concerned but. So if you have no bypass air/restriction (air cleaner for example)anywhere in the intake to turbo than it is possible that the MAF is a culprit. You could use logging function of the ECUtalk software so you could review the values of boost vs MAF voltages and RPM so you don't need to run a gauntlet on the road, not safe. What is the voltage when engine is not running just ign ON? If it is way above 1.0 V I'd be carefully checking the connector and the harness.


Cheers

Picked up a new MAF from Patrolapart in Lilydale today. Highly recommend these guys for their customer service, pricing and knowledge. Anyway, plugged it in, ECUTalk tells me voltages at idle are significantly lower (down to 2.1 volt). Start it up and drive down the road......the old truck is back! completely fixed. Thanks to all of you who offered advice, support and knowledge. Several of the symptoms were leading me a way from the MAF being the culprit, but there ya go....