Unexplained fuel cut

[tpi_roc]

Not a newbie but this is the most relavant forum.

I'm getting fuel cutt (like symptoms?) at about 4,500 rpms. The car hits a rock wall and will not push through it. I need some ideas, here's what I know so far.

20psi boost leak test passes with flying colors.

new BPR6ES plugs gapped to .025 and the wires are in great shape.

wastegate is connected directly to the compressor outlet with a very short vacuum hose, boosts around 10psi.

No shaft play (Just throwing this in for fun).

The only mods on the car are a K&N with a cutt can, and full exhaust.

The MAF has the silencer and lower honeycomb removed, nothing else.

The car seems to run slightly lean, the plugs were whiter than I'd like to see.

Other than the fuel cutt the car runs excellent.

I've got ECU capacitors in the mail, they seem to have just started leaking but the car doesn't show the normal symptoms of bad caps, going to replace them as soon as they get here.

Help me brainstorm, any ideas?

 

[neoviper]

Did you just start boosting 20 PSI recently? Also you didnt mention some sort of fuel management (DSM link, other). If you dont have this to stop the ECU from cutting off the fuel you will get fuel cut as you boost higher.

 

[tpi_roc]

Not a newbie but this is the most relavant forum.


20psi boost leak test passes with flying colors.


wastegate is connected directly to the compressor outlet with a very short vacuum hose, boosts around 10psi.

Please read above

 

[tpi_roc]

Nothing?

 

[GVR4592]

Do you have a real boost gauge or are you going by the stock gauge?

 

[drewvr4]

you might have the worlds largest exhaust leak

 

[tpi_roc]

Autometer phantom boost gauge


I don't suspect or hear any kind of exhaust leak, not saying I don't have one but I agree, it would have to be a HUUUUGE exhaust leak and I think it would be obvious. Besides I ran an open DP on my other DSM and never hit fuel cutt.

 

[vernvision]

I agree with the others you might look at exhuast leak between the head and manny and manny and turbo doesn't take much and you might not know it unless you look for carbon deposits from the leak. Other thing is try and get your self set up with a logger and check for diagnostic codes. A common fuel cut problem is the knock sensor. The other is the MAS. I have had problems with both and they were not tripping any codes. Bad injectors or fuel pump could also lead to fuel cut. Make sure you have enough fuel pressure and that the FPR is working right. The other problem is how you have routed your wastegate. Do you have a boost controller or are using the stock set up or nothing? If you are using nothing then that is your problem. There needs to be a bleed off valve on the wastegate side. If you don't then your BOV will open and you will loose all your boost. If you made your own then you will need to drill that nipple.

 

[tpi_roc]

I agree with the others you might look at exhuast leak between the head and manny and manny and turbo doesn't take much and you might not know it unless you look for carbon deposits from the leak. Other thing is try and get your self set up with a logger and check for diagnostic codes. A common fuel cut problem is the knock sensor. The other is the MAS. I have had problems with both and they were not tripping any codes. Bad injectors or fuel pump could also lead to fuel cut. Make sure you have enough fuel pressure and that the FPR is working right. The other problem is how you have routed your wastegate. Do you have a boost controller or are using the stock set up or nothing? If you are using nothing then that is your problem. There needs to be a bleed off valve on the wastegate side. If you don't then your BOV will open and you will loose all your boost. If you made your own then you will need to drill that nipple.

I'm not calling anything out, only looking for further details, please don't read me wrong

Fuel Cut

Address: 559A

Fuel cut is initiated when the calculated airflow goes over a set value, which is set at the address 559A. By increasing this to the maximum value possible (FF) fuel cut will be pushed off.

Another, possibly better, solution is to change the code in that area so that the ECU doesn't cut fuel regardless of the status of the airflow. This can be done by changing the "24" at 559B (which is a BCC code, or a branch when the airflow is greater than the value of 559A) to "21," which is a simple branch never code.

The code in the area looks like this:

02 D6 57 C1 A0 24 05 C6 28

Real "Fuel Cut" as DSMers know it is a protection routine built into the ECU for when the ECU sees more airflow than allowed. If this is the case I don't see how an exhaust gasket leak could cause more intake airflow than what hundreds, if not thousands, of DSMs modded more than mine with higher boost pressure, see before getting fuel cut.

For the knock sensor I haven't yet heard of a routine that kills the engine when a knock threshold is exceeded, which isn't a bad idea to have, do you specifically know of one you can reference?

As for injectors and fuel pump, of course not having enough is bad, however the only way the ECU is going to know that is via the 02, which should be open loop when at WOT, thus shouldn't be responsible for fuel cut.


I'll have to look into the wastegate thing and get back to you.....

Thanks for the ideas

 

[vernvision]

Is your MAS stock or have you modded it? I see you took the honey combes out. You might think about backing the screw out so you get more flow. When you start sucking that much air in you willl get the code you mentioned from just a few mods let alone more boost. I had the same problem when I went to HKS cams and a ported head. Even with stock boost I would get too much air going in for the sensor to handle and I would get instant cut the moment I went into boost. The solution was to run a hacked MAS in mine. I have PK issues with that though so I am having Nate at DSMchips.com make a chip that I can run a stock MAS. I will be able to run 20psi boost with it and not have the other issues associated with a hacked MAS. Just 2 more cents for thought.

 

[tpi_roc]

Not a newbie but this is the most relavant forum.


The MAF has the silencer and lower honeycomb removed, nothing else.

Also for the wastegate, right now there's no MBC or BCS, just straight from turbo outlet to wastegate, however the problem existed with the MBC inline, I removed it untill the problem is resolved.

 

[vernvision]

You can make yourself a manual boost controller for under $20 if you want to mess around but make sure you have a manifold hooked boost gauge if you don't already have one so you don't over boost.

 

[tpi_roc]

Posted above, I have an Autometer Phantom boost gauge

 

[vernvision]

If you can find someone with a 1g that you can swap MAS's with maybe you could see if that might be your problem. I have 2 or 3 of every sensor or main engine parts for these because you never know when you run into a wall like this. I have been there and fuel cut is a pain to diagnose at times. Since it appears that you are already running lean I suggest you get a FP gauge and a high quality adjustable FPR. I use one from BUSHUR Racing that works with the stock rail. The DSM that I still have I bought new in 93 and it always ran lean. It would glow cherry read after cruising it was bad and of course then and now the dealerships were no help. I am running it way modded and it runs cooler now then ever and a lot of it had to do with the lousy stock FPR. If I were buying another one of these and keeping it stock I would replace it with one from BUSHUR if that were the only thing I would do.

 

[tpi_roc]

I'll do a fuel pressure check tonight.



On the topic of the wastegate, how would connecting it directly to the closest boost source prevent it from closing?

 

[vernvision]

I am not sure about your question ont the wastegate but where you have it connected is the prefered way to hook it up. The closer and shorter the vacuum hoses are the faster the turbo hooks up. I have an aftermarket 2.5" pipe and I don't have that nipple to hook up to or I would hook mine up the same way except for the boost controller. I need to tap that and weld a nipple on one of these days! Anyway, The wastegate works under boost pressure not vacuum so when ever you boost it will open your wastegate and bypass the exhuast from the turbine. The bleeder in the MBC tricks this by allowing the air to leak out so it will not open the wastegate. There should be a check ball/spring like valve in the MBR which allows air to escape but not enter as then you would have a vaccum leak. If you don't block this off when doing a boost leak test you will hear air escaping and think you have a boost leak. Hope this answers your question.

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