Limp mode or something else?

GU IV 2005 DZ30Di
On the last trip home I wend to pass a B-double. Dropped back to 4th and hit the accelerator. Started to pass then nothing, no power. Foot off accelerator, down again all back to normal. Not a nice experience on a 2 lane highway.

No dash light I noticed and have NADS. Set to 15 psi.
No I was not looking at the dash. When you hit 110+km/h and passing a B-double the last thing you look at is the dash. Engine sounded ok and was pulling well till that hit. The only thing I can think off is I was getting close to the red line. I've hit that red line before and not had issues. From engine sounds not possible.

Got home and cleaned the MAF but this still does not make sense.
This was about 200km into a 400km trip so makes little sense. No problems after this either.

All a sort of one off nasty.

Any suggestions will be useful.

Limp mode mate. Either your MAF is on its way out or your Dawes is set right on the line of Limp mode and only when you really push the engine real hard your boost may just top over the Dawes set limit. Maybe just enough to set limp mode off.

Quote:

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Originally Posted by mudski

Limp mode mate. Either your MAF is on its way out or your Dawes is set right on the line of Limp mode and only when you really push the engine real hard your boost may just top over the Dawes set limit. Maybe just enough to set limp mode off.

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I will have to check service records but I thought I had put in a new MAF about a year ago, that replaced the original one. failing that new MAF.
Boost is set to 15 psi so the Dawes valve settings should not come into this I hope.

The parol does 110km/h happily but I have not pushed it at this speed in 4th gear lately. I normally start overtaking in 4th then flick to 5th at about 120 km/h. then shoot off at 130km/h. in this case dropped out as I started so about 115 km/h in 4th. Seldom hit really high revs.
Anyway back to service centre with it.

I might suspect old MAF and time for a new one.

Throw in an adjustable drag link and this cost to run as much as a mistress..
(At least patrol doesn't answer back or nag.)

My Dawes is set at about 14.5 to avoid limp while im waiting for my maf voltage modifier to be replaced. A couple of times I've hit limp mode. I've seen 17 psi on a cold night. It goes against the theory of a dawes but it seems the colder/denser air the more boost it will allow. Early mornings consistently see a brief 16 and power is better but know limp mode is close. Maybe yours did hit limp because its set close to the limit. Just a thought also is the spring in the dawes is metal. Metal changes characteristics with heat......

As pokey just mentioned, he has his set to 14.5psi. Some Patrols can only handle 14-15psi before limp mode, then I have fitted kits to Patrols that still didn't see limp mode at 18psi!
Its going to be either I suggested I reckon. Dud maf, again, or the dawes is on its limits.
Plus you don't need to see high revs to max out the Dawes. Just a heavy foot will do...
How often do you clean the MAF too BTW? Do you use MAF cleaner or something else?

If you say you think it redlined I would say it shut down as an engine protect feature

didn't know they had such a feature John. I have redlined mine a few times and nothing happened. Might be different on later models...

pretty sure they have an over rev thingy , read it somewhere
Mine did it once when selecting lower gear and forgetting about it

I had every thing checked 600Km before this occurred. MAF cleaned as well.
MAF cleaned every 5000Km.

It could be a simple case of having the boost accidentally set a over 15psi on the last check.
It had been OK for the last year, and has not occurred again, so just seems an odd thing.
I have red lined before and nothing has happened, no power loss.

So if the systems hits limp mode, which lights are supposed to come on?
I didn’t notice anything in this case.

Anyway back to workshop tomorrow for a recheck and test.

Need them to check a bit of oil on the intercooler intake pipe and some oil marks at the back under the intercooler. Some may be old stains before I dumped the Nissan intercooler.

Quote:

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Originally Posted by outback

I had every thing checked 600Km before this occurred. MAF cleaned as well.
MAF cleaned every 5000Km.

It could be a simple case of having the boost accidentally set a over 15psi on the last check.
It had been OK for the last year, and has not occurred again, so just seems an odd thing.
I have red lined before and nothing has happened, no power loss.

So if the systems hits limp mode, which lights are supposed to come on?
I didn’t notice anything in this case.

Anyway back to workshop tomorrow for a recheck and test.

Need them to check a bit of oil on the intercooler intake pipe and some oil marks at the back under the intercooler. Some may be old stains before I dumped the Nissan intercooler.

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No lights will come on when you hit limp mode....Oil in the intercooler is normal, sort of. It comes from the crank case vent tube that runs from the top of the motor and back into the air intake. To overcome this you install a catch can to filter the vapors before they enter the air intake.

Would appreciate update after you take it in. I thought I had mine sorted as mine hasn't gone in to limp for a few weeks since I dropped boost limit to 14 and slowed the spool slightly. Done a couple of 2 and 3 hour trips and towing a trailer and all good. Driving in Sydney today and went into limp. Got a catch can, just waiting to install on day off.

Limp like this is caused by either MAP (boost) above 17.9 psi or by MAF (air flow) where 3.99 V under 3000 RPM is obtained.
I suspect that you getting the dreaded Dawes bounce/spike where under certain condition the boost pressure hits over 18 psi briefly. This can happen if you have setup your Dawes during warmer weather period too. Cooler days make air more dense with more poke and turbo spools up quicker getting the overboost.

As already suggested you need to back the Dawes off a touch or have HD spring installed.

There will be no warning lights on the dash.

Cheers

Quote:

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Originally Posted by mudski

Oil in the intercooler is normal, sort of. It comes from the crank case vent tube that runs from the top of the motor and back into the air intake. To overcome this you install a catch can to filter the vapors before they enter the air intake.

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I have a catch can, sorry I did mean on the outside not inside, very fine smear.

Outcome:
1. codes checked: nothing
2. one of the hoses to the Dawes Valve had a crack. Possibly cracked at time it went limp.
Said it was the hose from the intercooler.

Anyway fixed so far.

Glad you fixed it outback.
Was watching this thread, to see the outcome. For a while there the slug moods my car was having (now fixed), I thought may have been limp modes.
My car exceeds 20psi easy when I let it. Even when mudski drove it the other day psi went through the roof and no limp mode.

As i said fixed so far.
Wont really know till I hit the highway next week and try passing a few B-Doubles or road trains.

Last night I hit limp mode. Made 17 psi in very cold dense air. One annoying thing about my setup is that I get cold limp often till the engine is up to normal operating temperatures. What's the criteria for cold limp mode?

Not 100% but I think you can go into a sort of limp mode if trying to rev to hard on a cold motor.
I think its just a safety thing same if redlining on a cold motor IMO

Quote:

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Originally Posted by Pokey

Last night I hit limp mode. Made 17 psi in very cold dense air. One annoying thing about my setup is that I get cold limp often till the engine is up to normal operating temperatures. What's the criteria for cold limp mode?

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MAF voltages are usual culprits, need to see if you are exceeding 3.7 V bellow 2,500 RPM or 3.99 V bellow 3,000 RPM.
One thing you do need to consider is the so called boost spike, anything over 17.9-18 psi and you'll get instant limp.The trouble is that this has the tendency to happen in 3rd gear uphill under the harder acceleration. I can almost reproduce it in another words I know I need to back off a little once I hit 2,700 RPM. Back off Dawes so your max spike doesn't pass 16 psi.

Cheers