Rough idle / backfire

[ohlegend]

My gst runs rough and if no gas is applied, will run for 30-40 seconds then dies out. If gas is applied, it backfires and smells rich. I have a clip of both instances.
First is it just running rough, the second is me giving it some gas.

98 GST bad idle/dies - YouTube

98 GST Backfiring/boggs engine. - YouTube

 

[AllanL]

recently changed the belts?

 

[bcowx06]

Are you using a 1g CAS? Also check your injector harness one could have cam off resulting in only running on 3 cylinders.

 

[ohlegend]

No, i have a new factory 2g CAS (just put it in)
The belts are all new too.

I will check the injector harness.

 

[Rsawd95dsm]

How are the injectors on the car? Still the stock ones with a lot of miles on them? Could pull them and clean them out. Here's a good write up on a good way to clean them. http://www.dsmtuners.com/forums/newbie-forum/448803-cold-weather-engine-issues-2.html#post153136134

 

[ohlegend]

Injectors are new (remanufactured ) stock

It gets to a certain rpm then it seems to miss and backfire. I had the same thing happen to my F150 it would get to a certain rpm then miss like hell, but once I got past that point they would work better. Coil pack was bad. I tested the spark on my GST, and got good spark. If the pack is going bad, I would still get good initial spark right? Then it would crap out under load?

 

[Rsawd95dsm]

Yes it could. If the coil pack had a small crack in it to it will go to the path of least resistance. I'd swap with a known good one and see how that goes.

 

[ohlegend]

I am swapping today. Fingers crossed

UPDATE: It does the same thing. The header paint melted off cyl. 1 & 4, but nothing on 2 & 3.
Any ideas?

I am running NGK bpr6es, since I have upgraded my intake and exhaust, should I go with NGK 7es?

 

[ohlegend]

Please Help!

 

[VtecvrsTurbo]

Did this problem occur directly after the CAS install or was that your attempt to fix it.

 

[ohlegend]

No, I have been having this issue for a while. even before I put in the new CAS. I just ran it long enough to get it that hot.

cyls. 1& 4 are running lean. (either no gas or no spark in those cylinders.