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Old 11-07-2019, 14:20   #1
Jay666d
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Default ZD30 - Limp.

I feel like the heading to this thread is more of a statement!

But I have a query/issue that I just don't know the answer too.... And I haven't been able to solve the issue with my Dawes Valve.

Let me set the scene:

In the morning I get in the truck to head of to work. I drive down my road which is a mile long 1st at 20mph, then it turns to 30mph, then to for the last 200 yards leading up to a T-Junction it's national speed limit. (I achieve around 50mph before I have to slow for a bend and then the junction right after.)

I wait at the junction for my time to pull out and when I do, this is where the problem happens.

The Truck is Auto, so it takes care of the gears. As it builds up speed and gets to about 40-45mph and the revs get to about 2500rpm up I'm at around 16psi of boost (Limited by the Dawes to 17psi) all of a sudden progression is halted!

I can keep my foot where it is and I will maintain the exact speed, like its hit a limiter or I can briefly ease off the accelerator, let the revs drop away put my foot back down and carry on gaining speed. (Every now and again, when I ease off and back on again, it might repeat the limiting process... But never more than twice in a row!)

If this is 'Limp Mode' then I thought setting the Dawes to 17psi would eliminate this? As I understand, the ZD30 usually creates 18psi and sometime spikes which causes the Limp Mode to kick in?

So this has me baffled... Any help would be appreciated.
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Old 11-07-2019, 16:37   #2
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Default

Reading a couple of posts on the Oz forums, one guy had a similar problem and he replaced the MAF sensor... Might look into changing that.
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Old 11-07-2019, 17:29   #3
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Angry This is why I hate modern cars !

TBH if either of our Jeeps had that issue I would have no idea where to start aside from obvious things like checking for loose turbo pipes etc.

To date the only no starts I have had with diesels has been flat battery and a recent fully blocked air filter. I am told to leave cleaning sensors to those who know how to do it as they can be damaged easily by the likes of me!

Am sure others here will know how to do some OBD stuff using paper clips & rubber bands.
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Old 11-07-2019, 17:44   #4
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Default

Is the manifold and exhaust system standard?
Mine would drop into limp mode when I had hole in the flexi-joint.
The inrease in gas flow is seen by the MAF and mapped by the ECU software to be in error.

Just another thought, 17PSI is very close to the point where the MAP sensor may come ito play, so a spike into and beyond is another possibility.
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Old 11-07-2019, 18:44   #5
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Default

Sounds like the classic overboost protection system kicking in tbh dude so may be worth a try at dialling the dawes back first before looking at anything that costs

If that doesn't change it then try the MAF?
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Old 11-07-2019, 20:23   #6
Mr K
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Default

Have you not just changed your downpipe?

As far as I understand it, the limp mode has nothing to do with the boost you are running, but all to do with what voltage your maf is reading. Hence why some people can run 20psi and some limp out at 15psi.

If your downpipe is in, it is that, if not, it could be the maf. But as rob said I would adjust the boost setup first.

I'd start with the needle valve as it seems it will be your spool up that's changed with the downpipe having a lot less back pressure.
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