1UZFE REVVING 6500-7K FOR NO REASON!

[spf_lexus]

So I have this ignition miss that has been a B**** to sort out for the last year and I need to find out whats wrong. I have been throwing money at this engine with new wires/plugs/dizzys/rotors and I have horrible misses around 1800-2200rpm. My WOT is fine, really pulls when I lay the pedal down all the way but if I have ANY LESS PEDAL, the car cuts off for a second until I either floor it 100% or lay off to 20%. I manage fine cruising around in this "all-or-nothing" situatuion but there's no way to compfortably part throttle over 2k.

-My first guess is my camshaft sensors... both have been sawed in half more than once from timing belt and this was from not re-routing the wires correctly. I re-spliced the wires and elec-taped but no sure if they are seeing electrical interference? The inner jackets of the cam sensors have a wire weave that I am guessing rejects interference?

-My second guess is my 16 year old ignition coils.. both are denso originals but don;t want to spend another $180 on coils if they are not bad. I have my battery re-located in the trunk and I have the main Positive lines routed to the trunk via nickel distribution block and three 4-gauge lines and the block inself is a matter of inches from the driver side coil... possible interference?



I do not have any vacuum leaks and my grounds are fine. I notice this miss when I am in a particular gear and need to open throttle w/o changing gears... and it feels like something is not in check. This always happens when im cruising on freeway at 75mph and I start to climb a hill and when the throttle opens to add air/fuel/spark to accordance to the increased needs of the incline but this is EXACTLY where I get the jumpy misses. I used to think the miss was ONLY at zero vacuum/zero boost hinting at a malfunctioning MAF but it also happens under vacuum cruising as well.

 

[Zuffen]

I'd be looking extra hard at those cam angle sensor cables.

Double check they are securely sldered together, twisting them together isn't good enough.

I'd also ensure the shielding is continuous over the joint. Even some aluminium foil wrapped around it will help.

Best solution is to try and find replacement wires for the sensors.

It's most unlikely both coils would fail at the same time.

 

[hi98gs]

I have also had the same problem since my rebuild. I still trying to find the cause. I have a "stumble/shake" when the car is cruising at 50 mph at 1500 rpm and on level surface. It will continue if I don't put more throttle and will go away if I tap on the throttle but will come back if I go back to "cruising"

I have already checked the ignition, and fuel. I haven't done anything regarding the cam angle sensors.

Please keep me updated with your progress in trouble shooting this.

 

[stevechumo]

Check the cams to see if they're aligned with the cam marks. You may take out the cam covers, set the engine at TDC, check to see if the rotor pointers (triggers) point directly to the marks on the cam housings. It'll be helpful if you can also run the timing light to get the idea.

 

[MWP]

Check your TPS too.
It could be setup wrong (or faulty) and telling the ECU you foot is off the pedal, when its really not. This would cause the ECU to cut fuel as it thinks you are decelerating.

 

[spf_lexus]

My TPS is brand new, I have it set and i have a nice mellow 700rpm idle, no stumbling there, and I played around w/ TPS for a while and it's not the root.


When I rebuilt my engine I sharpied my scissor gears and they went back in the EXACT same way they came out. I triple checked my timing and it keeps checking out. One thing is that I have taken off my timing belt tensioner many many times and is there any chance the spring inside is allowing slack? that could possibly cause the timing to throw off, but doubtful.

Zuffen- yeah they are just twisted and elec. taped. Honestly the first time I felt the bucking was b4 the blower was even installed... my timing belt sawed thru half a sensor and later half thru the other side. I have 2 sensors in the mail right now so we'll see.

hi98gs- does your engine run fine at WOT? Can you floor the pedal and still get it to move? Mine does but any less than 100% throttle does weird things...

 

[hi98gs]

My car runs fine throughout. It's just that when I am cruising I start to feel the "stumble/shake" The car runs fine on part throttle and accelerates well. It only happens when the throttle is held in place.

I checked my TPS and it is dead on. I used an OBD scan tool and it reads 15.7% which is within spec. I also checked with an ohm meter (the other option) and it read 1667 ohms which is also in spec.
Cam angle sensors are reading in spec.

This is also making me crazy.

 

[spf_lexus]

I noticed the same thing you have but it didn't seem to be as harsh as it is now. When I first noticed it I asked my passenger... "did you feel that? did we hit a pothole?"... thats what it feels like, as if the wheels broke loose for a split second. I noticed it climbing hills as I gradually increase my throttle. The symptoms tend to get worse as I climb elevation. My car runs excellent at sea level but bucks even more here in Colorado, which is 5,000 feet.

While I was feeling this miss I was in the process of my blower install so I ended up revving to a clean 7,000rpm before I even noticed it! I also failed my OEM head gaskets 2 weeks later. What keeps our engines' rev limiter in check? Are they somehow tied into the cam sensors? I mean, if the engine is reading a certain cam position thats false, could the ECU be thinking 6,000 when in fact 7,000? Interference seems like the cause if cam sensors interact with rev ceiling.

 

[spf_lexus]

Steve- when you refer to rotor pointers/triggers do you mean the arrow on the cam pulley to the 2 o'cloc/10 o'clock marks on the face of the head? basically I mean the stock tick marks for checking timing. I have not pulled off the dizzy and check orientaion of the trigger wheels.

 

[hi98gs]

I am not too sure what keeps the engine rpm limited. My understanding is that is a fuel cut on the oem setup. Don't really know if it is reading cam or crank motion to trigger the cut.

I currently running a full standalone setup. Initially was running the autronic SM4 but after the rebuild, the car started doing this. Even when we switched to the new ECU (ViPEC V88) it still did the same thing. So I doubt it's the ECU. I will try to recheck the sensors again.

Did you check the crank sensor?

 

[spf_lexus]

are you still using OEM MAF sensor or did you convert to MAP? I keep hearing MAP conversion is the way to go but have not tried yet.

 

[hi98gs]

converted to MAP.

 

[stevechumo]

If you look at the drawn arrows pointing to the slots on the cam pulley housings, you'll see they align with the triggers on the rotors. Also, the crank mark is aligned to the 0 degree, it is at TDC. You'll have misfiring if they're not aligned. The picture is just for reference, and I'm not sure those the OEM marks. I marked several of them and I don't remember which is the OEM slots by looking at the picture. I put everything back together awhile ago.

 

[cjsupra90]

Hmmmm, This sounds identical to the issue Matt (RedPhinonex) was having. As it turns out, it was simply the AFM module was not seated correctly in the AFM housing... His was doing the pretty much the same identical thing, it would miss anywhere other then idle and WOT. He had after going over several things with him, he had a feeling that it was the AFM cause when it was unplugged, the car ran fine except that it was in failsafe mode. So as a test, he swapped the AFM module out with a friend of his and the car ran fine so he figured it was time for a new AFM. So he put his AFM module back in to drive the car for the time being until he got ahold of a new or good AFM but the miss was not there anymore when he put his back in his car..
The only thing that makes any sense with it is that it wasn't seated correctly cause he took it out of the housing and basically put it back in and all of a sudden the miss was gone.
Not to say that this is your problem, but it does sound like the same miss problem that Matt was having so it might be worth a try....
I have seen this happen a few times on turbo 7M supras too being that they use the same type of Karman Vortex AFM.

One thing to note here (which might also have been Matt's issue) is to make sure that the module retaining bolts are not overly tight and that the torque is pretty even on all the bolts. The way the Karman Vortex type AFM function, if there is a distortion like one bolt being loose compaired to the others, it can destort the housing enough that the miror will not oscillate correctly at lower flow rates thus causing incorrect signal to the ECU.

 

[stevechumo]

On my SC and on 1 occasion that I forgot to plug in the MAF, the car ran very rich and eventually stalled.

 

[spf_lexus]

I'm waiting on replacement cam sensors, they have been rigged for too long and figure that these sensors should not be messed with. I suppose it could be a bad MAF sensor... there was a while back when I lost 1 of the 3 bolts that hold it in place but eventually replaced the missing one. Basically 1 bolt at each end instead of 1 and 2. So your saying that it's possible for the plastic housing to "distort" part of the sensor? I could see intake pressure + hot plastic + less mounting support to cause such a problem, too bad I don't know a single person out here with a 1uz lol.


I notice that on occasion if I modulate the gas juuuust right I can get a slow climb from idle to 3500 w/o any hiccups... but rare. Any chance the housing is leaking? what if I layed a bead of grey RTV and evenly tightened the sensor over the silicone to help seal it? I used an even layer on the top of the sensor to ensure no air leaks of the aging rubber top.


Cj- I used the RTV on my MAF top because I took it out and could blow air through a tiny crack in the rubber, so I sealed the entire top off, but from what I hear these sensitive Karman types don't take well to change... Anyone know what a new unit runs?

 

[spf_lexus]

Does anyone know if I can buy an aftermarket Karman Vortec type sensor and splice my plug to suit? I am aware hotwire MAF's from newer LS/GS wont't work but what about same type different brand?


Just found out $500 buys a new one... ouch!

 

[cjsupra90]

No, there are no direct replacement sensors that will work unless a "little Black Box" or sort is made. Unlike typical AFM's the Karmon Vortex type meter sends out a digital signal to the ECU where all the others send out an Analog signal. The ECU monitors the frequency of the digital signal to arive at a determined air flow amount. The Karman Vortex type of AFM uses a vortex generator to create vorticies in the air flowing through the housing. In the sensor module, there is 3 basic components used to generate the digital signal, an infered LED, a miror, and a infered photo cell. The vorticies created by the Vortex Generator cause the miror to oscilate and as the oscilates to one side, infered light is reflected from the LED to the Photo cell and as it oscilates back, the light wave is reflected away from the photo cell thus giving it an on / off digital pulse. As you probably figured, the more air that flows through the sensor hous thing, the more vorticies that are created, the more vorticies created, the more the miror oscilates, the more is oscilates, the more on / off cycles that happen from the photo cell and obviously the higher the frequency. And that ends todays lesson on the Karmon Vortex type Mass Air Flow Meter.

I dont recall if anyone has tried it, but I pretty positive that the MAFT PRO speed density conversion unit would work on the V8 TCCS's. There was also a converter that was commenly used on the MKIII Turbo supras that allowed you to use a common GM AFM inplace of the Karman Vortex unit which Im sure would work for the Lexus too. I dont recall what it was called or anything as I never got into that type of conversion cause I was Standalone EMS from pretty much day one with all my old setups.. I'll look around and see if I can find any info on the different supra forums and link you to it.

 

[stevechumo]

Sean,
Could you turn on the option to receive a PM? I have an idea and I have something to offer you..getting rid of things that I don't need.

 

[hi98gs]

After rechecking everything, I think I found the reason for the "stumble/shake" at cruising speeds.

Looking at all the plugs, I did notice that one plug was extremely foul compared to the others. I decided to change plugs. I used NGK 4554 (v-power heat range 8) as the replacement for the previous NGK 2668 (iridium heat range 8). The car ran fine for about 2 miles then all hell broke loose. The car wouldn't idle, and I needed to keep my foot on the gas to keep it from dying. I started to think :wtf1: . Did I blow the motor? Wasn't even boosting.

Next, I checked all the plugs again. Now all were fouled. So my next step was to check the coil packs. all seemed to fire well. But I did notice that the cylinder in question didn't seem to spark as brightly as the others. But I thought oh well it sparks.

Next was the injectors. I removed em all and had them professionally cleaned. The tech told me that the injectors were ok and none were locked open. Injectors were cleaned and I gained about 5-7% better flow from prior to cleaning. Injectors were reinstalled. Car still ran like crap.

Next was the driver. I also have an XS power pack iginition amplifier. I bypassed this thinking it may be the problem. No improvement. Then I checked the ground. . It was fair, but I decided to clean up the ground mounting point. Car ran better, but still wasn't feeling right.
OK, now here is the kicker


The last thing I did, just for giggles cause I needed a laugh, was replace the 3 mile old spark plugs, with the old iridiums. Started the car and it idled better. Drove it around, and no stumble, accelerated fine, no hint of misfire. So for now, problem solved.

Because I had ordered a coil pack, and couldn't return it, I put it on the cylinder in question. This was done far after the problem was solved.

I would proceed in this order from easiest to hardest.
1. check the ground
2. check the ground
3. use good plugs. ( I had no probem with NGK 4554 before, but it was always in other cars. I don't know if the 1uz VVt-i just is finicky with wanting premium plugs, but I am not gonna complain if it works well)
4. check spark
5. check fuel