MAF is FUBAR, where to from here? ~7psi procharged

[-Nemesis-]

MAF Problem. Help Please

Story/Rant:

I haven't really said anything about it, but my 4Runner has been running progressively worse since boosting. It has been getting a really bad miss around 2800rpm.

It started off gradual, noticed when towing the caravan at first that when the revs rose to this area going up a slight hill, the car would actually start slowing down again or not accelerate on LPG (say 100kmh 4th gear) and if I went back to petrol it would take off again.

To the point where now the problem is raising it's head on petrol too, and LPG can get so bad it farts and misfires like crazy under 3000rpm.

At the moment I am running a front mount intercooled Procharger p1sc that can hit about 7psi (at the moment, potential for more.) I'm running the stock Toyota ECU, as well as electronically injected LPG that has it's own ECU, it acts a bit like a piggy back to control the LPG off the signals sent to the petrol injectors (runs one fuel at a time, not LPG injection like diesels.)

So after many many many tests, I finally discovered tonight that unplugging the MAF means the problem goes away (kept it off boost for safety) and also felt gruntier down low running on the base maps.


This is where the question part comes in. I'm not really cashed up at the moment, but thinking about future tuning prospects I'm wondering what people suggest as ideas for me to do?

Should I buy a new MAF and be done with it? Should I look into going a MAP and MAftPro or something (don't know squat about this.) Other ideas?

In an ideal world i'd love a standalone and no maf, but it's a lot of money at the moment and my work is helping me feel the pinch of the current economy. Either way i'm up for some cash.

 

[-Nemesis-]

Thanks for the feedback!


Anyways, today is pretty demoralising. Put a new AFM on it and it runs just as bad as before.

Runs awesome without an AFM, and terrible with. But it still has been a degenerating problem. I'm totally lost to the cause now....

 

[spf_lexus]

Hey Nemesis thanks for bringing this up. I thought I had a miss somewhere else. I get misfires myself within the range you mentioned, and it's more frequent going up hills, or pulling a load right? And WOT is fine, no issues and plenty of power over here, gets down to 10 degrees at night . I checked all my plugs and no signs or arching. My wires are new but missing a rubber boot here and there (thought that was it).

Are you sure it's the MAF? So if I try and drive mine w/ plug unhooked it should go away? I wnna try this when i have time but I'm pretty sure the piggyack types have been known to swap from MAF to MAP which is more suitable for FI. I would like some more info as i don't know much about it either


Also, my misfires happen right as my boost gauge borderlines from Vac/Boost. If I keep pressing the pedal down it's not quite as bad but still quite there.

 

[-Nemesis-]

Yeah that sounds similar.

Mine started only slighty on LPG, but has been getting worse over the weeks to the point where it has no grunt under 3000rpm on LPG. And the misfires can get that bad it won't even accelerate. It also now does it on petrol. (Dual fuel, I can run on either)

When I unplug my MAF it goes awesome, it feels gruntier under 3000rpm than the engine ever has. Though if you try this, don't rev it into boost because I doubt it will get enough fuel on the ECU's base map (defaults to this if the MAF fails or is unplugged).


Problem for me is, it seems to be getting worse. Yet I just plugged in another MAF and the problem didn't change, it didn't even get slightly better. Oh and I reset the ECU before starting with this new MAF too. How the hell can it go perfect with no MAF, and be almost undriveable with one?

I'm a bit demoralised at the moment, so many things not working properly the first time on the car and in life in general lately. Just spent $600 getting the air con reinstalled, worked great for 3 days......

 

[spf_lexus]

Yeah I feel ya, I might try sealing the housing because mine is totally untouched. I have heard that MAF setups can be tempermental and I think a piggyback would solve it. It's more cheese tho, I dont have the cash for that right now either. It ends up being $600-700 for the unit, another $300 for a wideband so it can be tuned, and the costs of labor/install/dyno pulls i ends up little over $1000usd. Thats going to have to wait until summer for me. Mine sounds more mild than yours, I usually cruise at 2000-2500 and it's pretty calm but if I try and gradually climb into boost I get a few misses... but floor it and it totally flies, problem is sometimes I don't want to floor it and chug a gallon of gas to get on the freeway.


Any chance that our MAF is just leaking under boost? The housing was sealed for a draw through design... it was never really intended for actual boost. Natural engine aspiration pulls no where near as much air. I just feel the seal of the housing/sensor was designed to seal but not at levels we are seeing. If it is leaking it will be a very small leak thats only detectable on part throttle... that explains why there really isnt any issues with WOT, because everything unloads at once and fine tuning the gas might be causing the small leak to act like a feather in someone's ear.... just enough to throw the MAF off at low speeds as it is sensitive. Ever try a tube of silicone? I'll prob use RTV black and give it a try.

If you already bought another used one the fact still may remain that these units just don't seal under added intake pressure?

 

[-Nemesis-]

I'm not convinced that will be it, tonight mine is misfiring (i'm talkin MISSfiring, slowing down in 1st gear!) like mad at 1000rpm even, has no power....

Probably different problems.

Guys, when you unplug the MAF, what exactly does the ECU do? Does it only go to factory timing settings? Or effect more things?

If it's not the MAF that's dead, what next in line could it be playing up with?

 

[spf_lexus]

Dang Nem, I'm trying ideas in my head because I dont think we have the same problem but related. When my BOV wasn't setup right my car was UNDRIVEABLE over 3000rpm.... bov wasn't working properly and my car jumped and bucked everywhere but 1st gear power loss? IDK maybe a plug wire flip flopped? My next idea would be to test your tps.

 

[-Nemesis-]

TPS has been adjusted spot on with multimeter the proper way.

Plugs are new.

Leads are new.

It can't be a consumable like leads or plugs or rotors etc when you think about it, because it runs awesome without the AFM plugged in. I'm talking better than ever, before supercharger etc.

My only clue atm is MAF connected: runs bad, almost like the ignition is wet, have you ever had a wet dizzy in a car and you get that missfire where it wont build revs? MAF unplugged: mmm torque under 3krpm and pokey grunt, though I won't rev for safety.....

(thanks for trying to brainstorm anyways, keep it up!)

 

[kc95sc400]

Have not read the whole thread but, I've said it before and I'll say it again.

I had quite a few problems that I couldn't get to go away until I went MAP. The KV sensor was not built to have pressure on it.

I highly reccomend the Maftpro. maftpro.com.

It even has a Lexus MAF setting, thanks to me...hehe.

KC

 

[spf_lexus]

Kc- Thanks for the link, I got some good vibes from this site, and affordable. Which units did you need to tune yours? I saw one for MKIII supra but no 1uz. Also, I had heard that these MAF setups can be temperamental and that MAP was the way to go. Reason I feel my MAF is our issue is because mine only acts up as the sensor starts to detect boost, my
boost gauge will be hovering in between vac/boost so i think i figured it out. So you purchase one of their translators and then guy a GM sensor? DO I need just the translator? Or
do I need a controller too? Right now I have stock injectors and FMU, wideband and the works isn't quite necessary yet. I do like the fact that it retunes for larger injectors and
only costs $200.

 

[-Nemesis-]

Have not read the whole thread but, I've said it before and I'll say it again.

I had quite a few problems that I couldn't get to go away until I went MAP. The KV sensor was not built to have pressure on it.

I highly reccomend the Maftpro. maftpro.com.

It even has a Lexus MAF setting, thanks to me...hehe.

KC

Do you have a build somewhere that shows what you did and how? In regards to the MAP and MaftPro?

Problem for me is, going off the prices and the current $ conversion, by time I got a Maftpro and sensor here to Aus, I'd already be at 3/4 of the cost of a full standalone like Adaptronic.

 

[spf_lexus]

Our Karman vane type MAF sensor works great if we take our charger/IC off... it was made for flow... not pressure. Reason I almost know it's my MAF is because once my tranny cable was sorted out I only get these misses when my boose gauge drops all vac and is about to... crossing the line into boost and seems to smooth out the higher I climb into boost but laying off slightly under boost will cause more missfires. The MAP was designed to rear air based only on the pressure passing by. When MAF is changing from a rush of air going by to more of a pressure and the readings get thrown off and the ECU will compensate but I feel both of are seeing the sensor freaking out trying to read the change in incoming air.

 

[-Nemesis-]

I understand this yes, but the problem for me at the moment is my car hardly drives. I don't have a little miss, or surge, or hesitation because a MAF doesn't like boost.... My car fails to ignite half the time now when the MAF is plugged in, that's in revs well under boost levels, and at throttle levels well under boost level also, it's not boost related atm....

I need to try an diagnose what's going on, maybe I should start a thread in the Problems section, but i'd like this to turn into peoples ideas for finding out what's wrong. The main clues so far are....

*It runs fine without a MAF (though I wont boost it for safety)

*It can't be the MAF itself I think, because i've tried two and problem is identical

*I think that it runs okay with a MAF plugged in when the engine is cold (<60deg C)

*The problem has progressively got worse over the weeks, from a slight lack of power/miss at around 2700rpm, to the point now where sometimes the car wont accelerate it misfires that bad, it will actual decelerate at WOT.

Anyone got any ideas? What does the MAF talk to and what exactly does it control?

 

[kc95sc400]

What's up guys. I've been through quite a few problems on my car, so I'll share a few things. Maybe give you a few ideas.

Wideband - If you don't have one, you REALLY should. How else would you have any clue what's going on? Is the engine bogging rich or missing lean???

Codes - I assume neither of you have any, haven't seen any mentioned.

MAF - IMO, the Lexus KV MAF is just plain and simple, not designed for boost. If you are leaking pressure out of the top cover, it is toast. If you take the top cover off and look inside, you'll see that the sensing element inside of it is also sealed. If pressure is getting to the top cover then the inner parts are also leaking. As far as I could tell it's impossible to take it apart for a re-seal. I'd say about 80% of my driveability issues were solved by converting to MAP. BTW, I had also tried two different sensors.

IAT - Keep in mind that the intake temp sensor is also located in the MAF housing. On SC400's, the ECU assumes a temp of 68 degrees if the sensor is open / unplugged. You should test the sensor's resistance to make sure it's not shorted and to make sure the resistance isn't high. The IAT sensor is a major input to the ECU.

ECT - The engine coolant temp sensor is also a major input to the ECU and can affect AFR's in a major way. The ECT is used for just about every calculation the ECU makes.

FPR - If you have the stock fuel pressure regulator in place, check it. Mine was leaking boost but it held vacuum. This is bad for obvious reasons.

EGR - I assume you both have it blocked off. If you don't, do it. I wasn't able to make boost until I did.

Injector o-rings - Mine leaked pressure (air not fuel). I replaced them when I put the 315's in.

Vac hoses - It's worth it just to go ahead and replace them all with new. I had several leaks due to old, dry hoses. From my exp, a leak will cause the engine to run lean with vacuum and rich with boost.

PCV - I assume you both have sorted out the PCV system but it's worth checking. Don't forget about the passenger side (left hand drive) hose.

O2 sensors - Make sure that at very least, the front two sensors are good. I had found out that some weird things can happen with only one front sensor operational.

Ignition - This needs to work for obvious reasons. Don't forget to check the coils.

All I can think of for now, hope it helps.

KC

 

[kc95sc400]

*I think that it runs okay with a MAF plugged in when the engine is cold (<60deg C)

*The problem has progressively got worse over the weeks, from a slight lack of power/miss at around 2700rpm, to the point now where sometimes the car wont accelerate it misfires that bad, it will actual decelerate at WOT.

Anyone got any ideas? What does the MAF talk to and what exactly does it control?

Check the IAT and ECT first. Easy to check and one of them could very well be your problem.

Sounds to me like you're either running VERY rich (any black smoke?) or your timing is way off somehow.

I don't really know for sure but this is what I assume. Most sensors default to a certain value if there is a malfunction. The ECU cannot do this for the MAF sensor since it is constantly changing. I think that the ECU must use all good remaining sensors (O2, TPS, ECT, ect) do determine airflow based on a preprogrammed air / fuel map.

On my car, if I cut all signal to the ECU for airflow, it's not really driveable. Idles perfect and revs ok but as soon as you go over maybe 15% throttle, the egine falls flat on it's face.

KC

 

[-Nemesis-]

I'm not convinced it's the IAT because both MAF's did the same. One interesting thing though, because it looked a bit grimey I sprayed the MAF plug (on harness) with WD40 and it seemed to get back a lot of driveability...

Though it still feels less grunty in low revs than with the MAF unplugged.

When you went MAP; where did you mount it and what did you do about the IAT sensor?


Thanks for the big reply though!

 

[spf_lexus]

KC- If you don't mind can you lay down exactly what you had to buy/install for your MAP conversion?

 

[-Nemesis-]

I just coded mine and got IAT and MAF, but have tried two....

 

[-Nemesis-]

Cleared them, went for a drive and now the light blinks which means no codes....

Tell me a few ml's of WD40 won't be the answer to the main problem lol....

Off to go for a longer drive.

 

[kc95sc400]

Hopefully that fixes your problem -Nemesis-, can't beat that with a stick if it does.

I have the MAP sensor installed onto the big nipple on the front of the intake. It is the only thing connected to that port. When I still had the power steering vac switch connected to that port along with the MAP sensor, the car would stall when I turned the wheel. LOL.

I actually have a resistor installed on the IAT / MAF plug. The ECU always thinks the IAT temp is about 68 degrees. This is not optimal but hasn't caused me any problems. The MAFTPro does compensate for intake temps. I say not optimal because the factory computer likely pulls timing with higher temps.

I am using the fancier unit. http://maftpro.com/tproinfo.shtml I think the cheaper "translator gen II" unit would would work but I would contact them to make sure. I would assume that the Lexus MAF settings could be loaded on to it. The Pro unit that I have has allot more features but honestly I don't really use any of them.

I also purchased the IAT / MAP / wiring kit. I think any GM IAT sensor works. I also think any GM MAP sensor works, I have a 3bar. Good idea to buy the harness from them to make wiring easier.

It is also possible to use a different (GM) MAF sensor rather than converting to MAP. The unit can take the GM sensors input and convert it to a Lexus MAF output to the ECM.

KC