Miss off idle and under hard accel.

[Sawbladz]

So I've been having this problem for a while and I'm sick of it. It's time to get it fixed.

The car:
13 psi on stock turbo and fuel.
DDP and full exhaust.
Manual boost controller.
full hard pipes

The problems:

1. Off idle miss.

The car can idle fine at 800 rpm. If I give it a quick stab of throttle, the car will hesitate and then rev up normally. It will do this every time if I jab the throttle too quickly. If I slowly raise the RPM's, there is no hesitation.

2. Acceleration miss.

In most gears, more often 2nd and third, I can a miss under WOT. This miss is hard to describe. It isn't just one miss. If I go WOT and is begins to misfire, it will continue to do so until I let off the throttle. As soon as I let off, the car returns to normal. This miss happens whether I slowly roll onto the throttle or if I suddenly go WOT.

The odd thing is that this doesn't happen every time. There are some days where the car won't misfire once. Other days it happens every time. I hate it.

Today I changed the plugs just to see what they looked like. I was running champions and they all looked great when I took them out. I bought NGK's this time so I will see how they work out. All the boots were on securely and the wires are in great shape. (1 year old MSD's)

Any help would be appreciated guys. I'm not sure where to start with this problem. I should probably get a wideband...

 

[trydrew]

I'm having a very similar problem and would like to hear what others think it might be. I have replaced damn near every ignition part aside from my ignitor and my timing is spot on.

 

[turbojuiced]

I'm having a very similar problem and would like to hear what others think it might be. I have replaced damn near every ignition part aside from my ignitor and my timing is spot on.

Well just my opinion but if its not ignition time to start thinking fuel. Misfire is caused usually from ignition but could also be caused via fuel. May not be fuel to ignite? So have you tried running a wbo2? And if so what are the readings?

I would start looking fuel. For the OP I would start looking at ignition.

 

[Sawbladz]

Just to add to this. The car currently has an FCD. I know all about the drawbacks to this mod and plan to remove it in the near future. However, the car has run fine in the past with the FCD in place so I don't think that it is the cause of my problems now.

Also, I have a Walbro sitting on my shelf ready to go in w/ the 12 volt mod. Just wanted to figure out this problem first.

 

[turbojuiced]

Just to add to this. The car currently has an FCD. I know all about the drawbacks to this mod and plan to remove it in the near future. However, the car has run fine in the past with the FCD in place so I don't think that it is the cause of my problems now.

Also, I have a Walbro sitting on my shelf ready to go in w/ the 12 volt mod. Just wanted to figure out this problem first.

Well you need to first look into ignition and fuel. After you have done that then come back and let us know.

Preferably the ignition wiring, timing, and spark plugs.

Also on a side note the engine idling for the 7mgte is 650rpm by the tsrm. Also check for boost leaks.

 

[Sawbladz]

Spark plugs were just changed and looked great when removed. Timing is set to stocks specs. Spark plug wires are relatively new. I replaced the CPS last year with one that had perfect wiring.

Not sure where to start "looking into ignition and fuel".

EDIT: I wasn't sure what the car actually idles at, I ball parked it. I don't think it is quite at 650 though. Probably a bit higher than that.

 

[jetjock]

Does the accel miss start to happen around 3 psi of boost or it is really at WOT? No codes? 14 for example?

 

[Sawbladz]

Does the accel miss start to happen around 3 psi of boost or it is really at WOT? No codes? 14 for example?

I'm not sure. I will drive the car to school tomorrow and pay close attention so I can post a more accurate description. I know for sure that the turbo is not fully spooled but the throttle plate is fully open. I also don't believe this has ever happened under part throttle conditions.

 

[jetjock]

1) Check codes.

2) Temporarily jumper B+ to FP in the diag block and see if the problem goes away.

You could also do a snap throttle test while watching fuel pressure or pump current but if not just do the B+ to FP thing. It'll be OK to drive it like that for a day or two. Let us know what happens.

 

[Sawbladz]

Will do, thanks for the suggestions.

 

[s383mmber1]

Boost leak test performed?

 

[xcyanideslethalx]

i had the same type of problem before but it turned out just to be bad plug wires.

 

[Sawbladz]

Interesting. Drove the car to school this morning and it didn't miss once under acceleration. I will try again during my afternoon break. I still need to build a boost leak tester.

 

[ATL88Supra]

if it was a boost leak it would happen every time so quit askin about boost leaks....

 

[Amontgomery]

Will boost leak cause the problem in all gears/speeds to the same degree? I am having a similar problem that happens everytime I get on the gas over half throttle. But as the car actually increases in speed it becomes less noticeable, still there just less noticable.

 

[turbojuiced]

Interesting. Drove the car to school this morning and it didn't miss once under acceleration. I will try again during my afternoon break. I still need to build a boost leak tester.

did you check for codes yet?

 

[Justin]

I have had your first problem before.

I would hit the throttle really quick at idle. It would hesitate, almost bog down, then the RPMs would start climbing.


I bypassed the fuel pump resistor AND relay, and the problem went away 100%.