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2G Huge backfire, cutting out

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Wasteland

Proven Member
51
4
Jul 22, 2020
Pioneer, California
Hope someone sees this.

I have a 96GST That idles fine then a minute down the road it starts backfiring out the pipe and tries to shut off and sometimes does. But it will always idle ok. Revs up blow off does it’s job start going down the road plenty of power then starts cutting off then backfires over and over until you turn key on and off. If you wait about five minutes it acts fine again the the same thing?

I have two for spare so I’ll try whatever. Already check the usual. Timing plugs Wired’s vac leaks coils.... pressures. . Please help I am loosing it. Lol


Backfires out the pipe... not lip .... LOL

Not getting any codes forgot that .... duh o codes
 
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I would suggest you create a vehicle profile for the car and list ALL the mods in that profile: https://www.dsmtuners.com/dsm-profiles/

That info will help others see what you're working with so they can offer up advice. I'm assuming you've done a boost leak test. Was there any work done just before it started doing this? Was it driving fine up until a certain point?
 
Slowly learning site. Lol
I have 5 2g spyders of them 2 are GST.The one with wide body kit was just given to me. Lots of new parts rebuilt head. Under the dash was a nightmare of wiring. That’s when I found an older MAFT 1.3.
It’s doing something I have never came across in 30+ years of modding cars. It idles fine rev up fine then hold at 3000 rpm or drive for a couple of mins(time varies) and huge backfire and wants to cut out goes back to open loop then once it comes down it goes though same issue.

Check everything the usual sensors vac etc...
Any outside the box ideas..
 
Its been a really really long time but....
First things first, verify that everything is installed correctly. With the maft you need the gm maf and if you want to vent to atmosphere then the maf needs to be after the bov. Make sure you have the correct gm maf. There is a list somewhere on the dsmtalk website I believe. Boost leak test test test test.
Then i recommend hunting down some old instructions for the maft 1.3. There is a whole section in the instructions about how to tune using a maft. Also get a way to log. If you want to keep it old-school get a PocketLogger. I believe the maft has some dials and such on it used to dial it in.
 
How is the car tuned, since it's using a GM MAF?
Slowly learning site. Lol
I have 5 2g spyders of them 2 are GST.The one with wide body kit was just given to me. Lots of new parts rebuilt head. Under the dash was a nightmare of wiring. That’s when I found an older MAFT 1.3.
It’s doing something I have never came across in 30+ years of molding cars. It idles fine rev up fine then hold at 3000 rpm or drive for a couple of mins(time varies) and huge backfire and wants to cut out goes back to open loop then once it comes down it goes though same issue.
Check everything the usual sensors vac etc...
Any outside the box ideas..
What is being used to tune it, since it's using a GM MAF?
 
First idea, is to make sure that the BOV is routed back to the intake and not vented to atmosphere
That’s one of the first things is when I got the car home I rerouted all vac lines. It ran better but same issue keeps occurring.
UPDATE:
Completely retimed and it seemed to work. Drove great pulled strong for about 30 miles hen next day it was like I had never touch it... ABOUT TO TAKE 44 mag and see if that fixes it... LOL
Any advise even if it sounds dumb or even plain stupid if it worked at one time for you then you have my attention!!
 
That’s one of the first things is when I got the car home I rerouted all vac lines. It ran better but same issue keeps occurring.
UPDATE:
Completely retimed and it seemed to work. Drove great pulled strong for about 30 miles hen next day it was like I had never touch it... ABOUT TO TAKE 44 mag and see if that fixes it... LOL
Any advise even if it sounds dumb or even plain stupid if it worked at one time for you then you have my attention!!
Pretty much stock maf trans not connect. One thing I forgot to add is it is now coding EVAP Control or sending unit I think 4660 code have to check but it’s my bday and down cracking my brain for now!!! Great day for a ride taking the Ducati out a little 3 digit cruising... thanks for you time. We can do this....
 
So what is being used for the tuning? Stock MAF, injectors and pump? I don't see any of the fuel system or tuning tool mentioned in your profile. See if you can fill in more details about your set up.
It’s pretty much stock. I’m looking at it now. On the last few times it did it it has gone longer as far as it didn’t backfire after only a few minutes I went about 30 then it happened. Was bummed out. I did a reset and when it backfires it is throwing a cam senior code. I had a new one so I changed it even though that one was new, just in case, but didn’t change the issue.
*** Now, what would cause it to throw that code without that being the issue?
 
So stock 2g MAF, stock injectors, stock pump, stock regulator, stock ECU, stock everything except a GM MAF installed but not hooked up? And just to confirm, you did do a boost leak test? Do you have photos of the engine bay? Is the O2 sensor new? What are your plugs gapped at?

See this post about the BOV having RTV in the hole:
https://www.dsmtuners.com/threads/popping-backfires.197577/#post-1646360

What BOV is it?
 
check the cam sensor magnet is probably bad, this will cause backfiring and misfiring and sputter dying, this was the same problem my GSX had when I bought it from a kid, he did not know why it was doing it and ripping his hair out trying to figure it out instead sold it and it took me 10 mins to figure it out and 1 hour to replace the part, it's running like a champ now.
 
Ok
Stock MAF. Stock Ecu it it’s a 99 and I did the firing order and all that. Did a leak check and that was ok. Plugs gapped at 28. They were at 45-50 so not sluggish at at. Pulls hard up the back firing. Cam sensor just replaced. No vac leaks....
 
How is your fuel pressure? Maybe pull and test the pump?

I've read that a bad PTU can cause similar issues, noticeably worse when engine temps rise. That could explain why your issue gets worse when the engine is warmed up and tends to go away after you cool down for a few minutes. I saw you have several DSMs, maybe you can pull a PTU from another one and swap it?
 
Yeah I have plenty spares. Lol
Going to start again in about an hour and a half.
BOV Some aftermarket one. Do have to check pressure of fuel. I have AEM reg new in he box. Still coding EVAP and cam sensors. Cam code kicks in during/after backfire. I’ll add some engine pics or vid when I get home.
 
If you are still getting a cam sensor code even tho you replaced, you need to wipe the code. take a test start/run, see if it pops code again, if it does replace the metal plate the cam sensor attaches too (this is probably worn down so the new cam sensor will still mess up) The EVAP is not really a big deal and won't affect how the engine will run as long as the vacuum ports are blocked off properly and not taking in any unwanted air. the BOV should be recirculatory, but yours is blocked off seems you have Atmospheric BOV which is alright
 
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If you are still getting a cam sensor code even tho you replaced, you need to wipe the code. take a test start/run, see if it pops code again, if it does replace the metal plate the cam sensor attaches too (this is probably worn down so the new cam sensor will still mess up) The EVAP is not really a big deal and won't affect how the engine will run as long as the vacuum ports are blocked off properly and not taking in any unwanted air. the BOV should be recirculatory, but yours is blocked off seems you have Atmospheric BOV which is alright


Thank you for suggestion. Never have ever had this issue before in decades of wrenching. Always learning little details. Now....
The plate that attaches to gear(pick up) or is there a plate underneath sensor?
Going to find a vac diagram to see exactly which way to omit unneeded lines.
 
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Little update..... have not been able to work on it as much as I would like but have not had cam code as of yet after clearing again!!
 
Another update:
Going to switch to the 99 cam sensor. Looks Pretty simple and shouldn’t be a problem. I am using black 99 ECU after all.
If any issues that I may need to address please let me know..... maybe doing later tonight or tomorrow. Already pulled what I needed off the 99..... thank to all for input. I do think it maybe the pick up but also wanted to update to newer style cam sensor...
 
Another update:
Going to switch to the 99 cam sensor. Looks Pretty simple and shouldn’t be a problem. I am using black 99 ECU after all.
If any issues that I may need to address please let me know..... maybe doing later tonight or tomorrow. Already pulled what I needed off the 99..... thank to all for input. I do think it maybe the pick up but also wanted to update to newer style cam sensor...
Forgot to say that it did backfire but not as bad and it coded cam sensor again so that’s why focusing there....
 
Forgot to say that it did backfire but not as bad and it coded cam sensor again so that’s why focusing there....
Ok so did the change over to 99 cam sensor.
DO I HAVE TO CHANGE THE FIRING ORDER OR ANYTHING ELSE???
I am literally waiting on some answers please.....
 
Ok so did the change over to 99 cam sensor.
DO I HAVE TO CHANGE THE FIRING ORDER OR ANYTHING ELSE???
I am literally waiting on some answers please.....
Ok so changed the firing order back to what stock is for it to start and runs great little surges at idle but over all reading are were they should be. A/f and the basics.... but .... holding at anything above 3200 rpm and does the same old backfire BS.... so changing over cam sensor still didn’t change anything but still codes cam sensor. P0340 or something like that....
 
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