Limp Mode??

t0m541

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Mk5 Golf 1.9 110 (originally)
Hi everyone, it's been a while since I have posted on here, so Happy New Year to all.

Before you all slap me down for my thread title and tell me I should be in 101, it is performance related.

As you will see from my cars spec sheet I have done a lot of mods and the old shed has been running well till late, after last Kerma chips It was pushing about 165whp, and I was quite happy, so I just left it at that.

About 5-8 weeks ago I began to notice that at WOT and full boost, my boost gauge is marked to 25psi and the needle would fly past it to the stop, the engine would lose power, turbo would drop to nothing, then jump back to life and boost would come back, not slowly but instantly, like flicking a switch, 3-4 times in quick succession, so I would back off the throttle and just drive "normally".

It was getting more and more frequent so I just kept on driving around gently, I did notice a whistling sound when boost came up like air either escaping or a blockage boost side of turbo, as I had the IC piping blow off on the M-Way a few months ago I decided to have a look in them to see if anything was "laying" around and causing a restriction, and apart fom a piece of cord, that I had used in making the seals, wrapped around the anti shudder flap, lucky it stopped there. The only other stuff I could see was a good deal of oil in the pipework.

After a while I began to notice the car was less reluctant to go to full boost and I would have to feather the throttle to get it there, but when it did it would take off and leave a huge cloud of black smoke which it has never done since the remap, it has always run clean.

I was putting the intermittent power fluctuations down to the turbo playing up, maybe sticking vanes, but as the car was always driven in a lively manner I cant really see that happening, then most recent, when the temperature dropped in December, the car would lose turbo completely going up hills at about 2k revs and struggle up till I could cycle the ignition.

I Vag-Com the ECU and it said bad MAF so I dioded it out, which helped a little, the power loss got a little less frequent but still happened, so I had a look on here and found Canadian Grizzly's limp mode diagnosis thread.

So I checked and changed vacuum pipes, swapped N75 for EGR controller which gave a little more boost but still got power loss, (limp), so I replaced N75/EGR controller back where they should be and plugged them into harness so the ECU would still see them and bypassed the N75, vacuum straight to turbo, (max vanes), but was still only getting 10-15psi boost pressure and still power was cutting back once 15psi was reached, I assume the ECU cuts fuelling to try to reduce boost.

This lead me to the MAP sensor possibly reading high or failing causing the ECU to read overboost, so have tried driving with it unplugged, the car struggled to make any boost, and plugged in but taken out of pipework and hole plugged so it reads atmosphere only, car drove better until it reached the 15psi limit then power backed off, ECU reduced fuelling?, which is restored by cycling ignition.

So how does the ECU know that the boost is reaching the 15psi limit to back the fuelling off, when everything is disconnected and also is there a electrical mod/bypass for the MAP, or even some kind of workaround for this.

Any input or new angles on where the fault could be would be helpful, the hybrid turbo was reconditioned about 18 months ago so the diaphragm should be good although I have not got under and checked if actuator is moving, damn snowy weather.

I realise I could just spend cash and buy some new sensors/N75 but I want to buy the right ones as I have been pricing the devils up and they aint cheap but if I have to do that, 3bar map sensor is probably a good idea, (part nos. and where from please if anyone knows).

So guys what do you think??

Cheers

Tom
 
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t0m541

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Location
Teesside, UK
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Mk5 Golf 1.9 110 (originally)
Update

Ok, braved the snow today and had a poke under the bonnet and plugged in the laptop and and everything else under the lid as it should be.
What I found was that MAF was only reading 550mg/str, so dead MAF, the MAP was reading erratic to what was specified and not matching what the boost gauge was reading.
I re-diode the MAF (pins 4-5 bosch maf)and got 1275mg/str reading, no fault code flagged.
I took the car for a drive and I still got limp mode at 10-15psi on the boost gauge, cleared it on cycling on key.
So MAF and possibly MAP gone bad and the jury is still out on N75 although turbo is whistling away and obviously boost pressure is rising but not able to reach full pressure
MAF is bypassed now so need to work on either bypassing MAP or finding a 3bar one.
I read that there is a way of chemically cleaning the thrust ring and vanes on turbo, is this done in situ or out of car, should I find they are sticking.
 

t0m541

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Mk5 Golf 1.9 110 (originally)
News..but not good...
I managed to obtain today a replacement N75 and MAP sensor.
Fitted MAP sensor first with N75 bypassed(vac direct to turbo). Test drove car, still got limp mode (reduced fuelling), up hill or flat ground 3rd gear, any more than 2000 rpm and about 1 bar boost.
So I tried replacing the N75 and connecting it as it should be, test drive thought things were going well till tried to put some power up hill, .. limp mode(reduced fuelling, no turbo(N75)).
I then tried again without the N75 connected and found that if I tried accelerating gently on the flat I would get limp mode, but if I buried the pedal 3rd gear slightly downhill, after a bit of stutter at 2000rpm and 1 bar the turbo would go to full boost and hold until revs maxed out then boost would fluctuate, so I would go to 4th and keep the boost up and it would keep going without cutting fuel back.
I tried this a few times when I could, kept running out of road mainly, but each time I did I would leave a black cloud that needed radar to see through.
Now black exhaust is usually overfuelling or lack of air caused by bad filtration or lazy turbo.
But could it be that due to the lack of action caused by constant limp mode that the turbo and actuator ring are sooting up and when I do get full power it's burning the soot off creating smoke and if can keep doing full power runs without getting arrested, would it clean the turbo of soot and carbon and free it up.
Why would I get limp mode under partial throttle but not WOT when done quick, I have eliminated 2 of the suspects and the MAF is dioded out to read 1275mg/str max.

Any thoughts guys and my thanks to Kerma for continued after sales care...good customer relations :)

Tom
 

vwmikel

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'94 Golf Sport TDI
What you describe almost sounds like underboost. What is the specific code that it throws when it goes into limp mode?
 

t0m541

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I havn't Vag-Com'd it in limp mode yet, it's something I will try tomorrow, my laptop has a dead battery so has to be on mains power, so I'll get the PC ready and take car out and put it into limp then keep it that way so I can get it on my drive to check it out.
I was getting a MAF fault (impluaseable signal), but cleared that with diode.
 

t0m541

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as for the underboost, I was thinking that...if the ECU map is looking for X=boost and the turbo isn't spooling then it would throw it up, however the boost gets to 10-13psi quickly and is responsive to throttle input, so vanes must be catching exhaust flow efficiantly, also on quick WOT it will spool to full boost, now, corect me if I'm wrong, but exhaust flow is directly proportional to fuel/air input and combustion, so if the ecu is reducing the fuel input then the resultant exhaust gas will peak lower and fail to provide enough flow to spool the turbine up to full speed regardless of vane position, vis-a-vis underboost beyond the 1bar threshold, when the ECU map is looking for more.
Vicious circle, ECU then reduces fuel as it detects a fault and cuts vacuum to diaphragm closing vanes.
So could the original fault lie in the fuelling side, insufficiant fuel??
Just bouncing ideas here
Tom
 

vwmikel

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'94 Golf Sport TDI
t0m541 said:
as for the underboost, I was thinking that...if the ECU map is looking for X=boost and the turbo isn't spooling then it would throw it up, however the boost gets to 10-13psi quickly and is responsive to throttle input, so vanes must be catching exhaust flow efficiantly, also on quick WOT it will spool to full boost, now, corect me if I'm wrong, but exhaust flow is directly proportional to fuel/air input and combustion, so if the ecu is reducing the fuel input then the resultant exhaust gas will peak lower and fail to provide enough flow to spool the turbine up to full speed regardless of vane position, vis-a-vis underboost beyond the 1bar threshold, when the ECU map is looking for more.
Vicious circle, ECU then reduces fuel as it detects a fault and cuts vacuum to diaphragm closing vanes.
So could the original fault lie in the fuelling side, insufficiant fuel??
Just bouncing ideas here
Tom
It all has to do with the time limits and allowed deviation set forth in the software. The MAF issue may be related to a boost leak which could also cause the underboost error.
 

t0m541

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The MAF, when I last VC'd it live data didnt show above ambient pressure regardless of airflow, 550mg/str constant and whilst plugged in showed fault code. How would a boost leak affect the MAF as they are in separate parts of intake system, pre and post turbine.
What about a software glitch in the ECU map, somehow cause by a voltage spike or a degradation of the EEPROM structure.
Or something more mundane, fuel filter collapse/clogging restricting supply to pump?
 

t0m541

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Hmmm...fuelling fault....now I think about it, more fuel makes more compression, bigger burn, hotter gasses, more power, more exhaust, more flow to turbine...restrict that fuel amount and its going to peak...but why at 2K rpm, 1bar boost under load?? and not downhill fast action WOT, what controls fuel flow inside pump on fly by wire pumps apart from ECU/TPS inputs?
 

vwmikel

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t0m541 said:
The MAF, when I last VC'd it live data didnt show above ambient pressure regardless of airflow, 550mg/str constant and whilst plugged in showed fault code. How would a boost leak affect the MAF as they are in separate parts of intake system, pre and post turbine.
What about a software glitch in the ECU map, somehow cause by a voltage spike or a degradation of the EEPROM structure.
Or something more mundane, fuel filter collapse/clogging restricting supply to pump?
Your MAF may well be dead, but 550mg is the default value. So, if it throws a code it will just stay at 550mg all the time. Also, if you happened to have a boost leak then the MAF may read very high in comparison to the boost pressure. In this case the ECU would see this correlation as being implausible. When your car is in limp mode it will not be requesting boost and bypassing the N75 may cause additional faults as it is not expecting to see it.

Voltage spikes causing corruption of the eeprom seems rather unlikely. And, if such a thing were to occur I believe your first indication would be a checksum error. In this case the car either would not run at all or would run with a constant error code that won't go away. Let's not get into the unlikely just yet and stick to the more likely scenarios. :)
 

t0m541

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I do have the MAF dioded out to read 1275mg/str, I have read the thread on here regarding MAF/Diode mod but I don't think there was any reported cases of limp mode, I could be wrong, will re-read thread.
However, surely once the rpm and demand reach into the higher band the MAF report would then start to match fuel map required flow, hence reported, in MAF thread, "once rpm reached 2K the car took off", it would as intake flow(what diode/MAF says)/MAP sensor reading and fuel flow match the ECU curve.
 

vwmikel

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t0m541 said:
I do have the MAF dioded out to read 1275mg/str, I have read the thread on here regarding MAF/Diode mod but I don't think there was any reported cases of limp mode, I could be wrong, will re-read thread.
However, surely once the rpm and demand reach into the higher band the MAF report would then start to match fuel map required flow, hence reported, in MAF thread, "once rpm reached 2K the car took off", it would as intake flow(what diode/MAF says)/MAP sensor reading and fuel flow match the ECU curve.
It may well be that it won't throw a code because of the MAF reading too high. The only way that you're going to know for sure what's happening is to check the codes and do some logs.
 

t0m541

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Hi, Ok did a limp mode fault code reading tonight and this is what it found :- 16485 - Mass Air Flow Sensor (G70): Implausible Signal

P0101 - 35-10 - - - Intermittent.
Without cycling the ignition, the fault code refused to clear and MAF was reading default 550mg/str, when I cycled the ignition, the MAf went back up to 1275mg/str and I code cleared the fault and it didnt return.

So any thoughts and ideas
 

KERMA

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Hi Tom- Maybe it's time for an updated tune that totally disregards the flaky mass air sensor and uses the MAP sensor to control the smoke based on your boost signal. True Speed density control in your case would be cheaper than buying a new maf. Please E-mail me and we can discuss the particulars.
 
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vwmikel

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KERMA said:
Hi Tom- Maybe it's time for an updated tune that totally disregards the flaky mass air sensor and uses the MAP sensor to control the smoke based on your boost signal. True Speed density control in your case would be cheaper than buying a new maf. Please E-mail me and we can discuss the particulars.
Did you figure out how to block the MAF codes? If not then the CEL will still be there.
 

martytdi

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This is getting common, and the problem could be simply the plug that goes into the MAF or the wires. They are replaced at times for a reason. I hope it helps.
 

Diesellover Andy

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1997 green passat wagon, 2010 Jetta Sportswagen
Limp

t0m541 said:
Hi, Ok did a limp mode fault code reading tonight and this is what it found :- 16485 - Mass Air Flow Sensor (G70): Implausible Signal

P0101 - 35-10 - - - Intermittent.
Without cycling the ignition, the fault code refused to clear and MAF was reading default 550mg/str, when I cycled the ignition, the MAf went back up to 1275mg/str and I code cleared the fault and it didnt return.

So any thoughts and ideas
I have same thing.97 passat.Only happens with boost above 18 psi.Didn't spend much time on this-just some.I feel that it must have something to do with air volume.I hope that your fix will work for me too.At 25 psi you shure run out of the road quick .Especially down the hill.No limp below 18 psi.
 

t0m541

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Hi folks, thanks for all the input. Kerma I will email you.
Ok update, I went back to the breakers and pulled a MAF from the car that I got the other bits from, (map/N75).
Things improved, slightly, got better boost, although not max pressure and still getting limp mode.
At first I left all connected, (map/N75 etc), but as limp cuts turbo I have again bypassed N75, as we all know these engines are sluggish at best without some forced air, or at least mine is!!!.
I had a decent run down the motorway, when I go to WOT with this MAF power and boost just climbs slowly and quietly to about 18psi, where as before all these problem, the power and boost was like flicking a switch accompanied by loud turbo, and as I hold the throttle WOT I am getting epic clouds of black smoke, that make following cars drop back!!, so not good, (ok for speed cameras though :) ).
So I am either getting an overfuelling problem or insufficiant air delivery caused by turbine not spooling to full speed and I think that as this MAF seems good then limp is now being "possibly" caused by low boost.
Is it possible for the exhaust side of the turbine to soot/carbon up badly enough to slow its rotational speed, could it be even with N75 bypassed and max vacuum to diaphragm, that the vanes are not fully deploying so causing most of exhaust gasses to be dumped straight down exhaust.
Is there a fix for that scenario that doesn't require the ball-acher of a job of stripping the turbo out and taking it to bits, (mucky, oily, fiddly sharp edged, pain in the arse, back of the engine thing!!!!).
 

t0m541

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OK PROBLEM SOLVED.....

After reading the thread on chemical cleaning of turbo, I decided that this was worth trying as my EGR is just a blanking plate now==easy application of cleaning solution.

As we dont have Easy Off this side of the pond I got Cillit Bang, same company similar chemicals(just no foaming agent, trigger spray).

So I decided to brave the cold as it was a sunny day and give it a go.

However, as I was stripping the top end of the engine to get access to EGR plate, I removed the top IC pipe(the one connected to manifold). Once this was off I discovered an inch long split on the innermost radius of the pipe.
When the pipe was in place the split couldn't be seen and as the curve was under compression it was tightly shut, but obviously under boost pressure was letting air escape.

This is where the sluggish and low boost was coming from!!!

So I fixed the pipe, while it was off I checked the travel of the actuator on turbo and it was nice and free, so I left the cleaning.

I plumbed everything back up, MAF,MAP,N75, took the car for a drive and wahooo it's rocktship time again.

Now everything was working I tried the diode in the MAF again to judge the difference, and there was quite a marked difference.

With the diode in place, performance was down, acceleration was sluggish and boost was lower.

So I took it back out and put good MAf back in cleared all codes and shut the lid.

I do have one further question for the tech boffins. On the side of the MAF(Bosch) there are 2 copper connectors, about halfway down the MAF body and there is a circuit diagram depicting a (Diode/Resistor), that can be, presumably, put in series between these 2 connectors on the outside of the MAF body.
I have put a picture of these connectors in my gallery for clarification.
These connectors are linked to pins 1 & 3. Pin 1 on my harness plug is empty so it doesnt do anything, but what are these connectors for, any ideas guys, I assume that on some VAG all 5 pins must be used.

So thanks everyone for your input on this matter, Kerma I am still interested in MAF software delete, email sent.

It goes to show that sometimes you can look too deep into a problem when the obvious is right under your nose, like accidentally pressing (function+f7) on your laptop, which toggles mousepad on/off, then spending next 3 weeks stripping/rebuilding with new parts, re-installing bios and OS, only to discover your original error and that it was too simple a solution to be seen.

GRRRRR lol

Tom
 
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KERMA

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Hi Tom, glad it all worked out.
Nonetheless, I think you will enjoy driving your car when the smoke map is referenced from the boost signal instead of the mass air flow. It tends to wake 'er up quite a bit!
 

t0m541

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KERMA said:
Hi Tom, glad it all worked out.
Nonetheless, I think you will enjoy driving your car when the smoke map is referenced from the boost signal instead of the mass air flow. It tends to wake 'er up quite a bit!
Thanks Kerma, Email sent :)
 

t0m541

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vwmikel said:
Did you figure out how to block the MAF codes? If not then the CEL will still be there.
I re-read this tonight, on my car I don't get a CEL when I get a fault code, it does work, but it has never come on.

I just thought I would mention it.

Tom
 

t0m541

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New Chip/Tune no MAF

KERMA/Charlie....All I can say is "you have done it again":D.

I installed the new chips/tune today that references the boost signal from MAP sensor that you wrote for me.

What a difference in performance :D. The car was quick before, but now it's so much more, stronger power, crisp throttle response, higher boost, acceleration in all gears right through rev range.

I haven't been able to give it full power test as the weather here is freezing with snow and ice, so not too keen on putting car through a hedge but where roads/traffic have permitted the results have been superb, overtaking is literally stamp and go, no wind-up/lag at all.

It is comparable to driving a petrol turbo. As a mechanic I have had the pleasing opportunity of driving Evolutions/Imprezzas/Skylines/Pulsar in various states of tune and the power delivery is on par with these....most pleasingly!!!

Kerma/Charlie thank you :D
 

t0m541

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Its Back

:mad::mad::mad::mad: Last night a "boy racer" in a big bore Vauxhall decided to have a pop at the old man in the diesel, so I WOT in 4th@2500rpm, as the revs got round to about 4k there was the little blip in boost drop, went to 5th kept WOT max boost from about 2k rpm, got to around the 3.5k rpm and boost dropped off, came back, dropped off about 3-4 times in quick succession, then the glorious LIMP MODE came back, "boy racer" way down the road by this time :eek::eek::eek:.

I have fitted new 3bar map sensor, N75, vac pipes, actuator is nice and free, MAF delete re-map as described in previous post.

So any new ideas????.

My boost gauge is reads to 25psi and at full boost the needle goes past 25 and carries on to the stop, I am going to locate a high reading gauge to see how much it's really pushing, as the only possible explaination I can think is that it's spiking way past the 3bar, I know that at full steam the boost screams, like high pressure air!!!

What is the max boost pressure one of these engines will stand before it blows seals/gaskets etc, I dont drive the car flat out often, but would like to be confident that I can when I need to with it embarassing me, by either blowing up or having the performance of a dumper truck when it limps modes.

:confused::confused::confused:

Tom
 
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