Help needed: S13 CA18DET choking under boost, probably unmetered air, no more idea.

[robymus]

Hi!

I'm running a 200SX RS13 with CA18DET, mostly factory spec, except a new air filter, big front mount intercooler, oil catch tank and custom piping for these installed, and also my battery moved to the back during this.

After this modification, a strange thing happened, when the engine comes up to boost (around 3000 rpm), it will go suddenly lean and starts choking.

Here are the things I know:
- I have a wideband O2 sensor installed, and it shows very lean condition (18 and up)
- I have Nistune ECU upgrade (factory map), and I have logged the voltage from the MAF, which drops suddenly when boost comes (to around 3 volts, see attached log), so ECU thinks it has less air (throttle closed?) and reduces fuel amount, this leads to lean condition
- Boost looks OK, not dropping, going up to 0.6-0.7 quickly and smoothly.

I was thinking of pressure testing the intake piping, I asked my mechanic to test for me, and he said he did and there is no leak, but I don't believe him, I will try it myself once more.
I have replaced the MAF, with a second hand (original spec) one, the effect is the same.
I have checked the ground voltage drop, could not do on the MAF, but on the harness and a few other places near the MAF, it looks good. I'm not sure if I checked correctly, I followed some instruction on the net, also the accepted values were from some forum, which I don't remember, but my measured value was about 60 mV.
Voltage looks stable (also datalogged)
I have tried to disconnect the oil catch tank line feeding back to the intake piping (also replaced the oil catch tank and lines)

My mechanic checked the fuel pressure and said that it's insufficient, and suggested to change the fuel pump. We will do that soon, and also install a new fuel pressure regulator, to be sure. But I think it can not be related, as the metered air amount is dropping, this could not be the cause, maybe a secondary problem. Or can it be?

Now I have no more ideas. I have found the IACV-Air regulator valve now, which feeds from (or to?) the intake piping, so I will try to investigate, but I don't have high hopes about this.

Do you have any idea what can be the cause for this? Anyone seen something similar? Where should I start?

Any idea appreciated.

http://r2.io/img/maf_err.png

[Croustibat]

Hi!
- I have Nistune ECU upgrade (factory map),


What is your ECU number ? 44Fxx or 39Fxx ? i know the microcode is different; i had a 44F but i switched to a 39F for various reasons, one of them being nistune and most tuning software use the 39F memory map, and the 44F has some differences (like the speed limit value address ... )

You probably have a boost leak somewhere, and you may be hitting the fuel cut too. Once you have your fueling / leaking problem sorted, change the max load value (which is usually refered to "fuel cut", but "fuel cut" in nistune is not that; this one refers to the rpm/load the ecu will cut fuel when decelerating).

OEM fuel pump is known to fail over time, so get a better one. Sometimes the wiring is too weak for uprated fuel pumps, so check the fuel pump voltage at the plug near the fuel tank and replace if it drops.

If changing the fuel pump does not fix the problem, change the FPR with a good one. A lot of people here claim their FPR is no good, when in fact it comes from a weak pump that does not flow enough. dont get an ebay special ... a WORKING FPR is worth at least 80$. Stay away from 30$ jobbies.

I would like to know what your fuel pressure is too. "My mechanic said it is too low" is not enough ... CA18DET base fuel pressure is 2.5 bar, when on most engines it is 3bar. If your mechanic does not know that, he may be mistaken.

You may also simply have a clogged fuel filter ...

This :


I have tried to disconnect the oil catch tank line feeding back to the intake piping


is creating a massive boost leak. The thing is, there is no oil catch tank on the CA, so that is aftermarket. How are its hoses routed ? Please take pics.

You may have no boost leak when not on boost, and then have one when it comes on. It would explain why your mechanic said there was no boost leak.
Check the 1way valve, at the back of the intake manifold. It is where the venting hose connects.

Lastly, get that tuned correctly. The OEM timing is very conservative, the fueling is insanely rich, and with a FMIC you need to rescale your TP values as you will be out of bounds when it works properly. But you cant tune until you fixed the previous problems.

[robymus]

Thanks for the information.

I will continue to look for the boost leak.

I have a Tomei FPR on the way, I plan to install it, together with a Walbro fuel pump. I will keep an eye on the fuel pump voltage. I will update this thread as soon as installation is done (probably early next week, as post is very slow)

I would like to know what your fuel pressure is too. "My mechanic said it is too low" is not enough ... CA18DET base fuel pressure is 2.5 bar, when on most engines it is 3bar. If your mechanic does not know that, he may be mistaken.

I think he was talking about 32 psi (2.2 bar) at idle. I could not verify the exact value, as I could not reach him, and I couldn't test it myself yet (my car is at the car audio shop now, they are removing my subwoofers, to access the fuel pump).
Thanks for the guideline on the pressure.

I was thinking of the fuel filter too, so it was replaced, and did not solve the problem. Now I have a brand new Z32 fuel filter installed.

is creating a massive boost leak. The thing is, there is no oil catch tank on the CA, so that is aftermarket. How are its hoses routed ? Please take pics.

It is routed like this diagram:

http://r2.io/img/oilcatch.jpg

I have tested with disconnecting it from the intake pipe and venting to the air, and sealing the intake pipe connection. All the same. I will take a picture of this when the car gets back.

Lastly, get that tuned correctly. The OEM timing is very conservative, the fueling is insanely rich, and with a FMIC you need to rescale your TP values as you will be out of bounds when it works properly. But you cant tune until you fixed the previous problems.

Yeah, I will definitely tune it, as soon as this nasty problem gets fixed. Thanks for the tips, I will keep you posted on the progress.

[robymus]

What is your ECU number ? 44Fxx or 39Fxx ? i know the microcode is different; i had a 44F but i switched to a 39F for various reasons, one of them being nistune and most tuning software use the 39F memory map, and the 44F has some differences (like the speed limit value address ... )


It is 39F05, a think my nistune came preprogrammed with the same map.

But actually this problem came before installing Nistune, I have installed Nistune as I thought it could be fixed by tuning (as you said, installing FMIC will require tuning), but could not proceed with tuning due to the MAF reading inconsistency.

[robymus]

I would like to know what your fuel pressure is too. "My mechanic said it is too low" is not enough ... CA18DET base fuel pressure is 2.5 bar, when on most engines it is 3bar. If your mechanic does not know that, he may be mistaken.

Got the final value, under boost it was 38-40 psi (2.6-2.7 bar).

This sounds good for me, so I'm afraid the problem will be somewhere else.

[Croustibat]

This may be too low ; your fuel pressure should be 2.5 bar + intake pressure. If you are boosting 1bar, then your fuel pressure should be 3.5 bar at full boost. At idle, you have something like -0.7bar at the intake, so fuel pressure should be 1.8bar.

I still dont think the FPR is the cause though ... try a new fuel pump. Beware of tomei FPR, most of them are fake. If it has fancy colors, it is a fake.

I did install an SR20 FPR, to get a 3bar base pressure instead of 2.5, and it perfectly does the job. It is way simpler to install than an aftermarket FPR, just make sure you get the SR20 bolts too. You need to chop the lower metal tube of the FPR and ovalize the 2 bracket holes. And then bolt it again.


Quick question : do you still have the hot start solenoid ? If so, delete it. It is known to cause problems. If your fpr vacuum reference line is directly connected to your intake manifold, then it is already deleted. If not ... well you know what you have to do :D connect it directly, and block the lines of the HSS.

I need to go, but try this.

[robymus]

This may be too low ; your fuel pressure should be 2.5 bar + intake pressure. If you are boosting 1bar, then your fuel pressure should be 3.5 bar at full boost. At idle, you have something like -0.7bar at the intake, so fuel pressure should be 1.8bar.

I still dont think the FPR is the cause though ... try a new fuel pump. Beware of tomei FPR, most of them are fake. If it has fancy colors, it is a fake

Thanks for the info, I see how it may be too low now. My new fuel pump will be installed next week, so we will see.. The Tomei FPR is coming from FRSport, they are quite reliable with not selling fake, and it's gray.


Quick question : do you still have the hot start solenoid ? If so, delete it. It is known to cause problems. If your fpr vacuum reference line is directly connected to your intake manifold, then it is already deleted. If not ... well you know what you have to do :D connect it directly, and block the lines of the HSS.

I need to go, but try this.

I think I do have, I don't know about deleting it, so I will go and check (and delete if it's still there).

Thanks for the pointers!

[robymus]

Good news: problem solved.

We have upgraded the fuel system - new fuel pump (replaced wiring too), fuel lines, fuel pressure regulator. To be sure, rebuilt the intake piping from the airfilter until the turbo.

And now it works fine. At least it feels good, I didn't datalog it yet, will get to it soon and start playing with mapping.

Thanks for the ideas!

Ah, and I didn't have the hot start solenoid, so at least didn't have to check that).

[azmi604]

I bought an s13 its been a week or two. Its the same problem as yours. I think. I hope. I have the same problem as this. They said its the TPS sensor problem. I'll try to upgrade the fuel regulator and everything. Thannnkkk youuu!!!!


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[shogun!]

Quite often it is a problem caused by removing the oem filter and attaching a direct air version. The air stream disturbs the MAF sensor.

[azmi604]

Quite often it is a problem caused by removing the oem filter and attaching a direct air version. The air stream disturbs the MAF sensor.

I didn't change the filter. Well, the person before me didn't. He changed the intercooler thats it.


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[azmi604]

Owh yeah i did install a boost meter. I don't think I installed it properly. I use the vacuum from the front lower throttle body. The first one in front.


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[914Slide]

Owh yeah i did install a boost meter. I don't think I installed it properly. I use the vacuum from the front lower throttle body. The first one in front.


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that's where mine is seams to read good.

your problem is solved i have a similar issue almost the same really it just flats spots the afr and still pulls i don't wanna hurt the motor. I have changed my entire fuel system at this point!:facepalm: