2G 99 GST Cylinder 3 Misfire

Tanro · Feb 18, 2017

I've got a 99 GST with a 16g running wastegate pressure. It has a cylinder 3 misfire code, and is missing in boost underpartial throttle, wot, and sometimes rarely out of boost at low throttle or idle.

I've replaced the plugs with NGK bpr6es and gapped @ .028. I have good NGK Wires, coils ohm out correctly. I've tried swapping the wires, swapping the coils, and swapping injectors. It still has a cyl 3 misfire. I've verified timing marks are correct and performed a boost leak test. My only leak is the throttle body, which I'm not sure if its the freeze plug for the IACV, or the shaft seals. I am going to pull it off and seal the freeze plug with some RTV. The FIAV has been closed down by removing the plug and turnin the adjustment until it is bottomed out, and the coolant lines removed.

Could a boost/vacuum leak from the throttle body be the main cause of a Misfire?

I also verified fuel pressure at idle, I am getting 37-39 psi with the regulator hooked up, and 44-46 psi with the regulator vacuum line pulled and the port capped off. Seems to be doing its job, fuel pump seems to be supplying plenty of fuel. Reall quite stumped as to what the cause could be.

spyderdrifter · Feb 19, 2017

Check the ignition power transistor as well. It's the part right next to the coils, and has a long rectangular plug.

WhiteTalon007 · Feb 19, 2017

Heres a pretty good thread about the ignition power transistor.

http://www.dsmtuners.com/threads/ignition-power-transistor.395895/

Tony818 · Feb 19, 2017

Woa. Sounds like you pretty much covered everything. Im suprised its still misfiring. The power transistor would be a good place to start in your shoes. How many miles are on the car? And does cylinder 3 have any compression at all?

Tanro · Feb 19, 2017

Tony818 said:
Woa. Sounds like you pretty much covered everything. Im suprised its still misfiring. The power transistor would be a good place to start in your shoes. How many miles are on the car? And does cylinder 3 have any compression at all?

110k on the chassis, but I've had to replace the engine due to rod knock, Miller Imports sold me an engine with ~90,000 miles. I compression checked it after swapping it, from cyl 1 (timing side) its 180, 179, 179, 178.

Thing is that the problem was there before the swap as well.

As I understand, when the Ignitor goes it usually starts having problems with 2 cylinders. Is their anyway I can test the ignitor besides swapping it for a known good one?

spyve4 · Feb 19, 2017

How many mile have you put on the new engine since you had it installed? Are the injectors stock? Do you have to add coolant? Leak down test could tell you a little more.

Tanro · Feb 19, 2017

spyve4 said:
How many mile have you put on the new engine since you had it installed? Are the injectors stock? Do you have to add coolant? Leak down test could tell you a little more.

A couple hundred miles. No the cooling system is fine. It holds coolant to 26 psi which is as high as my testing set registers on the gauge.

I was experiencing misfire on the old engine before it developed knock.

Murdertalon · Feb 19, 2017

you could use one of those in line spark lights to make sure its firing.. if you put two of them on and noticed that cly3 was firing erratic that points to the coil or transistor, barring that leaking caps on ecu?

also maybe check out that your fuel injectors are working properly.. you could use noid lights on two of them at a time while cranking the car and see if they are firing even

Tanro · Feb 19, 2017

I guess I am just going to need to source an Ignitor and try swapping them. Coils are new 3000gt coils. I had a set of 3000gt coils from an old build, but they compatible. I just swapped them onto the 4g63 coilpack bracket.

Tanro · Feb 20, 2017

I am thinking it may just be related to my Intake leak at this point. The LTFT and STFT are still trying to pull fuel, and its still running very rich.

Murdertalon · Feb 21, 2017

Tanro said:
I guess I am just going to need to source an Ignitor and try swapping them. Coils are new 3000gt coils. I had a set of 3000gt coils from an old build, but they compatible. I just swapped them onto the 4g63 coilpack bracket.

Isnt that coming off of a v6? I cant comment on if they are in fact correctly compatible maybe someone else can chime in?

Have you checked ECU caps? I have read enough to know they can cause odd behavior.

Tony818 · Feb 21, 2017

You should stick to OEM coils specifically designed for the dsm. Are you in colorado? I have my engine apart if youd like to try mines on just to see if that does anything

Tanro · Feb 21, 2017

They are the same coils. Land Rover's use them too. If you purchase a single coil, instead of a coilpack, you get the same part number. These just so happened to be an entire coil pack from a 3000gt that I had handy from an Old Build I parted out. So I have a spare, I tryed swapping that on today. No improvement.

I did however notice the car runs like shit before it warms up when its cold, or very humid outside.

I have the parts store running a can of MAF cleaner and a New coupler for the Intake to my shop tomorrow morning. Will see if cleaning the MAF helps at all, once I get my new STM throttle shaft seals, I am going to pull the throttle body and replace the seals and reseal the FIAV freeze plug with RTV Silicone.

Those nickel and dime trips to the parts store hurt a Lot less when your parts store brings stuff to you, and you've got a decent discount.

Tanro · Feb 23, 2017

Cleaned the MAF and replaced the intake coupler. Still no better.

Only things left it can be are :

Power transistor (Igniter)
o2 sensor
Bad Maf

Or more likely. My throttle body is leaking to the point its causing a misfire. The low rpm, low load mis goes away once the car starts to warm up. But it still has issues in boost. But its not hitting fuel cut, and its not an every pull thing. Sometimes it is worse, sometimes I can pull wot to redline with no issues.

f***ing intermittent problems are the worst.

Well hopefully I can fix my leaking throttle body, and do another BLT to see what else leaks. Right now the TB starts leaking ~ 8-10 psi. But i've run with leakier throttle bodies with no misfire or fuel cut issues in the past.

cheapracer · Feb 23, 2017

Intermittent problems are the worst. It seems to me every time I've had something like this it's been an electrical gremlin. I'm curious if the ecu is running the number 3 injector properly?

Tanro · Feb 23, 2017

It doesn't seem to be having issues. I pulled the ECU out and opened the case. It looks fine.

I will take a log with Evoscan tomorrow and post that.

cheapracer · Feb 24, 2017

Here's my line of thinking:
Same problem with a whole different engine, indicates something that is the same between then and now.
Intermittent fault indicates it's probably not mechanical/rotating assembly/compression.
Fault is not global; only one specific cylinder affected, even though you swapped injectors, plug wires.
What's left really?
That's why I question the ecu.

kanusky1990 · Feb 24, 2017

What ECU and CAS are you running?

Tanro · Mar 14, 2017

kanusky1990 said:
What ECU and CAS are you running?

Stock 99

It was the coil. I did some swapping of coils, and whenever i swapped coils the cylinder 3 misfire would get worse.

I ordered a new set of coils, and once my coils and mass airflow get here i will report back. But I did finally narrow down the issue to my coil. The secondary coil on 2/3 was about 2 kilohms lower than the 1/4 and all of the other coils I had were worse with either the primary, secondary, or both being way out of spec.

But we did manage to get a really nice pull @ 22 psi by gapping the plugs to .022. Then we burnt out the Mass airflow. So we got one of those ordered as well.

10's or bust · Mar 15, 2017

Tanro said:
Stock 99

It was the coil. I did some swapping of coils, and whenever i swapped coils the cylinder 3 misfire would get worse.

I ordered a new set of coils, and once my coils and mass airflow get here i will report back. But I did finally narrow down the issue to my coil. The secondary coil on 2/3 was about 2 kilohms lower than the 1/4 and all of the other coils I had were worse with either the primary, secondary, or both being way out of spec.

But we did manage to get a really nice pull @ 22 psi by gapping the plugs to .022. Then we burnt out the Mass airflow. So we got one of those ordered as well.

More than likely the coil finally burnt out since it was faulty anyways

Tanro · Mar 15, 2017

10's or bust said:
More than likely the coil finally burnt out since it was faulty anyways

No the coil is still the same as it ever was. It is fine under certain conditions.

The mass airflow is shot though. It is reading IATs but airflow is showing a steady 0hz and 0 grams per second.

Boostedmm17 · Mar 20, 2017

Mines doing the same thing, it idles terrible too. So was my buddy's talon and I used his maf and mine was running exactly like his. After like 3k it would run okay. So did the maf fix yours?

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