UNSOLVED MIStery. For those who want a challenge, I need major help.

[J DAWG]

I have continued to have a high rpm mis. Above 5500 rpms under load(WOT) and sitting still revving the motor(no load). I have a 2001 with a set of heads(ported/polished, bigger vavles, standard deck height) ans a moderate cam. Belanger headers, Roe oval cats, and Corsa catback.

My engine has 8 to 9 inches of vacuum at idle. My short term adaptives are -10% and long term are -33%(maxed out way rich). My MAP sensor voltage is around 4.3 to 4.7 volts(WOT)

My air'fuel with a wide band is around 11.2 to 11.6 above 5000 rpms. My a'f readings are from 3rd and 4th gear runs with the sensor in the passenger side ********* right before the collector.


My fuel psi is around 52 psi prior to the missing and then it becomes irratic when the mis occurs. The needle bounces from side to side very fast.

My injector pulsewidths are real similar from bank to bank until it starts missing then they may differ by more than 1 millisecond above 5500 rpms...ie: left side 21.5ms and right side 23ms at 5700 rpms.


The car ran fine prior to installing VEC2 and Innovate wideband. Once I started logging air/fuel with the VEC2 installed, I began having this mis even with stock settings in the VEC2. Once I started adjusting the VEC2 it became worse. Timing adjustments didn't affect the mis, however fuel adjustments(taking away or adding) made the mis worse and for some reason taking away fuel produced severe spikes in my air/fuel graphs and adding fuel only made small areas of "hiccups" or "breakups" or "missing" even though my air fuel was way rich.


What have I tried???

-removed VEC2
-resoldered all wires that were tapped into(cam position sensor, crankshaft pos. sensor, MAP sensor)
-changed plugs(new champions twice and now running a colder NGK)
-changed plug wires(Magnecor 8.5 and stock wires)
-changed fuel filter
-added MSD fuel booster
-adjusted fuel adaptives prior to removing VEC2 back to 0%.
=tried another 2001 pcm
-tried 1998 pcm
-compression test(all cylinders around 170psi)
-visually inspected vavle springs and checked roller rocker adjustments.


Plan to do a leakdown test and change batteries. Need to get to a dyno, but have not had time since they are hours away.

Again the car ran fine with the stock fuel system and above mods prior to VEC2 installation, but even with NEC2 off the mis IS more subtle but stillthere.

Also if I run the car and shift around 5500 rpms all is well, but if I hold it out to where it begins missing and shift then it continues to mis into the next gear.

Big thanks to everyone who has helped thusfar. I greatly appreciate it.


Signed,
MISSING IN MISSISSIPPI
John

 

[Qualitywires.com]

Sounds like your cam sensor or crank sensor is bad.

 

[J DAWG]

definetly is a possibility. Up until this point I have not changed any sensors.


My scan tool says voltage to them is good, but I don't think that means they are ok???



I messed with the cam position and crank pos. wires, but resoldered them back.

 

[Qualitywires.com]

I bt you that the sensors are not picking up a signal at times or certain RPMS. This sounds exactly what my car went through and I changed my crank sensor and the problem went away. If it happens at certain RPMs, I'm almost sure that is it.

If you are testing the sensor while the car is cool...then it probobly won't show anything...do it when it's hot it might...but it only happens at those certain RPMS like you said.

 

[J DAWG]

Are the crank sensor and cam sensor difficult to change?

 

[J DAWG]

ab


did your car set a code when your sensor was bad?

 

[Qualitywires.com]

no it's real easy my friend! Crank sensor is on the passenger side engine block by the 02

and the Cam is up front on the timing cover. By the water pump.

 

[Jim Wilson]

I'm new at tuning A/F ratios, so this is just a thought and probably wrong, but here goes.....Try adjusting your short and long term trims so that they are closer to 0 (+10 to -10 total). Since your running so rich in closed loop, maybe it is affecting open loop (or higher rpm settings)???

Another idea might be to check your A/F ratio with your LM-1 on the driver's side.

And if that fails......replace your piston return springs

 

[Qualitywires.com]

I can't remember if it set a code off or not. it probobly did.

 

[Jack B]

J Dawg:

There has been no explanation of the irratic fuel pressure, this could be the cause, not the symptom. There is almost nothing that can cause the fuel pressure to swing except a bad pump/regulator. Even with the car missing the fuel pressure should stay between 50 and 55 psi. It is electric and is not related to the engine rpm or misfire. Either the pump or electrical feed (or pump control)to the pump is faulty. That boost-a-pump circuit is not a fix for a bad pump or regulator.

A separate issue is your injector pulse width, they are maxed out or static. They are no longer spraying. This is a stretch, but, could the puddling of fuel contribute to the issue or be a parallel problem. In the static state your fuel adjustment via the VEC becomes meaningless and hit/miss relative to what the result is. This sounds exactly was is happening in the description of your fuel adjustment.

 

[Qualitywires.com]

Well, I took some time and got out the old book for ya to help ya out in case it's a cam or crank sensor...hope this helps you out and gives you an idea of where it's at. Isn't your car under warranty? If so go get the part and install it. It will take 30 mins tops!

You must be registered for see images

You must be registered for see images

 

[1TONY1]

When I had a miss, the fuel pressure needle would go nuts.

 

[J DAWG]

I'm new at tuning A/F ratios, so this is just a thought and probably wrong, but here goes.....Try adjusting your short and long term trims so that they are closer to 0 (+10 to -10 total). Since your running so rich in closed loop, maybe it is affecting open loop (or higher rpm settings)???

Another idea might be to check your A/F ratio with your LM-1 on the driver's side.

And if that fails......replace your piston return springs

Jim



I was thinking the same and I did set the adaptives to zero with the VEC2, but the car still missed. Something at the point of installation occured.

Maybe at that point something got a surge and shorted out.....a sensor a fuel pump or something else electrical....I dunno.

 

[J DAWG]

Jack, I honestly don't understand what is going on, but have felt it was fuel related.

I am going to speak with a fuel guy tomorrow and review everything with him and maybe get a better understanding. All I know is I would rather buy a GTS before I change the pump on my RT


ab - thanks for the pics of the sensors. My dealer here ***** and I don't think...well I know they would not warranty the sensors even though I have the maxcare warranty. Maybe another dealer would. That would be nice.

 

[Daniel Cragin/DC Performance Inc]

Give us a call, maybe we can help.

 

[J DAWG]

this is not a good sampling of my air fuel at the present time. This graph was with the vEC2 and my a/f was all over the place. HOWEVER, what I wanted to point out was my RPM logging. I am logging from the cam position sensor and you can see how it losses signal around the 5700 rpm mark, AND another point is that this has occured on probably 50% to 60% of my graphs. Looking at my graphs it usually losses signal anywhere above 5500 rpm.

 

[Nadine UK GTS]

As the man himself says...give Dan Cragin a call! I had problems with fuel supply and injectors, he sorted me out with a better fuel system and better injectors. Thanks Dan. Jacks comments are also spot on.

 

[Jack B]

J Dawg:
Where is the O2 sensor located on that log.

1Tony1:
In your example of fuel pressure taking wide swings, could the fuel pressure be causing the misfire. On the other hand how could the misfire cause the fuel pressure to swing. When the regulator is working it doesn't care what the engine is doing as long as volume is not exceeded. A misfire might cause the fuel pressure to bounce, but, the regulator is going to recover and maintain the pressure in that range of 50-55.

 

[Viper Specialty]

I have a spare Crank Position Sensor from a 2002 GTS if you need it. I will cut you a deal on it... most expensive sensor in the car!

 

[Miles B]

That looks like the same 2 points in the other thread, where the "V Notch" is happening. I have no idea why a cam or crank sensor could just lose it at those two engine speeds though?

The fuel pressure needle thing does seem strange... maybe it is going nuts because of sudden changes in flow? Like the injectors stopping opening or going spastic out of order is setting up weird pressure waves up and down the fuel rail?

Those 2 notches being at the same 2 RPMs (well, close anyway) as the other thread does seem like a big coincidence though.

 

[Sean Roe]

Hi John,
Based on your graph above using the cam sensor as your RPM input, I'd definitely change the cam sensor, or swap it out with a known good one to test.
Put your logger back on and record a run afterward.
Hope that's it.
Regards,
Sean

 

[Mike Adams]

Not likely a crank or cam sensor either the work or they don't in most cases. What wires have you tapped into when you installed those two items ? Call me i have run into the same issues and spent allot of time working on the theory of how the computer works. With two signals going irractic the fuel and cam sounds like a bad connection. The fuel, spark and injector pulse can be affected by certian signals. You are going to need an ohm meter and an oscilliscope to check it properly.

 

[Mike Adams]

Are both side adaptives the same ?

 

[Sean Roe]

Mike,
The VEC2 is off the car and the problem persists.
If the cam sensor is loosing signal, maybe there's something going on with how the sensor is picking up off the cam. It is an aftermarket cam.
The notch in his log is telling us something.
regards,
Sean

 

[Mike Adams]

I saw that after Sean sorry. Can you tell what side the miss is coming from (Do you have a cross over pipe in your exhuast ?)

 

[J DAWG]

J Dawg:
Where is the O2 sensor located on that log.

Jack, my o2 sensors on my Belangers are in the uppermost hole only reading #3 on the drivers side and #4 cylinder on the passenger side.


Months ago I swapped them around to the lower hole, which I think reads the front 3 cylinders on each side, trying to get rid of a check engine light.

 

[J DAWG]

Not likely a crank or cam sensor either the work or they don't in most cases. What wires have you tapped into when you installed those two items ? Call me i have run into the same issues and spent allot of time working on the theory of how the computer works. With two signals going irractic the fuel and cam sounds like a bad connection. The fuel, spark and injector pulse can be affected by certian signals. You are going to need an ohm meter and an oscilliscope to check it properly.

Installing the VEC2 I had to splice into the Crankshaft sensor wire since I did not have the correct connectors at the time. I bought the unit 2nd hand and did not realize the special connectors existed. Since then I have resoldered the crankshaft sensor wire.


For the wideband I tapped into the camshaft sensor wire to log rpm, but since then I have removed that wire and resoldered the cam sensor wire.

I also tapped into the MAP sensor wire for the VEC2 connection, but since then have resoldered it back.

At this point I have no sensor wires tapped into. Everything has been resoldered and put back to stock, but maybe a sensor is bad.

I can hook up my scan tool and log some and record voltage to the sensors and see what that shows.



Sean - I plan on changing these 2 sensors as well just to rule it out. Thanks


John

 

[J DAWG]

I saw that after Sean sorry. Can you tell what side the miss is coming from (Do you have a cross over pipe in your exhuast ?)

Mike I have Corsa on the car. As I am driving or revving I personnally don't know what side it is coming from. I need to get my wife outside to rev it up for me and stick my face in front of the pipes and see which cheek lights up first, which may not be a bad idea. Sorry for the humor, I am just a little frustrated at this point.


Thanks for your help.
John

 

[Larry Macedo]

One thing to keep in the back of your mind is this... A sensor can be faulty and not cause the MIL or "Check Engine Light" to illuminate. The sensor can still be faulty and work within it's set parameters.

 

[J DAWG]

took the car by a local gearheads shop today to let someone else listen to it. He said the mis or cutout sounded more like firing and not fuel. As he revved the car up everytime it missed/cutout at the same rpm(5100ish), but cleared up around 5200ish and then missed/cutout again at the 5600 mark.

His first suggestion, after knowing what all I have tried, was the cam sensor.