6G Celicas Forums

Hello everyone,
I have a 1998 Celica GT auto with the 5sfe engine and I was merging on the highway so I decided to floor it but when it got to the 4000 rpm I heard a loud "pop" from the engine bay. Sounds like it came from the intake. Plus, it wouldn't shift and seem like it was hitting the rev limiter. So I wanted to see if anyone can help me with that.

Mods: Injen short ram intake and custom 2.25 exhaust.

Sounds like it backfired through the intake. Do you have any codes? When is the last time things like spark plugs and wires were changed? Any other issues prior or since? Usually backfire through the intake is a timing or run lean issue.

Or worst case you have valves sticking.

This post has been edited by Box: Mar 3, 2017 - 1:20 PM

Well, I haven't scanned it yet since the CEL isn't on. I changed my spark plugs and wires, valve cover gasket, transmission filter, and fuel filter all last summer/fall. And when I was changing my fuel filter I kinda twisted the fuel line a little bit so don't know if that would be the cause.

On a side note: The engine is a replacement one since my last one had a cracked head and was leaking oil.

If the fuel pressure is dropping that'd cause it to run lean and backfire.

If plug wire order was off that'd be another possible cause, but I'm sure it'd have done it before now if that were the case.

Well, the issue has been since the new motor got put in. That's why I did all the mainetance to see if it would get fixed but so far no luck. So whenever I want to merge or pass a car and just punch it, the same issue always happen.

Does it run normally otherwise? It kind of sounds like the valve timing is off a tooth.

If it's under 4000 rpm then it's fine but anything above doesn't shift or always "pops." So not sure if all auto does this or not.

I'd double check timing marks then if it's been doing it since it was put in. If the timing was never done the belt could've let timing jump a tooth.

This post has been edited by Box: Mar 4, 2017 - 1:27 PM

Thanks for the advice but since I'm not mechanically inclined how simple of a job would this be?

This may have happened for several different reasons:
Timing
Timing belt issue
Weak fuel pump
Low fuel pressure
Incorrect air/fuel ratio
Bad catalytic converter
Bad or cracked spark plug
Bad injector(s)
If it was my situation i would do all the inexpensive things first:
Check fuel pressure at speed and hi rpm
Check spark plugs for cracked porcelin and gap
How old is the timing belt

Check your:
Fuel pressure while driving-
Remove spark plugs and check for cracks in the porcelin and check the gap
Have your catalytic converter checked also

Well if you have to redo timing it's somewhat involved, here's a writeup for the MR2 but it's still a 5S so everything pertaining to the engine itself will be the same: http://bobaab.awardspace.com/timingbelt/timingbelt.html

As stated before, when I did my fuel filter I kinda twisted the fuel line a little bit but this issue was happening before I did it. So I doubt that was the main problem from the start. And when I got my custom exhaust I also got a new catalytic converter put in but I've had this issue before all that. I might have the check everything again like you stated. When the new motor got put in I just assumed that they replaced everything so I don't really know if it's old or new or if it was replaced at all. The mechanic seem kinda shady to me. But thanks for the tips.


Thanks! I also remember seeing a video on Youtube about changing the timing belt on a 5sfe so I might look for that too.