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car backfired after timing belt

21K views 54 replies 15 participants last post by  2geclipsed  
#1 ·
so here's the story. my crank pulley separated on me, and I was trying to install a new fluidampr. In the process of checking the timing components, we noticed that the idler pulley had significant play - the new belt was put on 5k miles ago.

we decided since we had the cover off to replace it. We marked the belt in all of the right places, and loosened tension on the timing belt to get the idler on. we got the auto tensioner back on, it was just around 4.5mm - and seemed close enough to spec acorrding to the vfaq. all of the timing marks lined up accross the board, so we put it back together with the new idler and fluidampr.

we then tried to start it up, and the car kind of puttered a bit, and had figured it was because it was the first time the car had been started since October, so I continued to try to start it. after the third try, out came a loud ass backfire. Now when I try to start it - it does't sound like it normally does - almost like it has no compression. we checked the timing marks, everything still lines up on the cams, and on the crank pulley's notch that lines up on the timing cover.

Right now we are thinking that maybe the belt may have jumped a tooth. would this cause the car not to start? am I looking at possible bent valves because of the backfire? could it be bad gas - since it was sitting for nearly 9 months?

we did try to crank the motor by hand afterwards and we were able to feel the compression cycles while turning it - is it true that if you can turn the engine by hand, and feel the compression, that could mean that the valves and pistons are still ok?

we are going to try to a compression test next week to see what's going on. we are thinking maybe a bad injector, but something tells me we did something wrong with timing.

any thoughts?
 
#3 ·
The only way to verify that timing is correct is to pull the cover off and look at the actual crank timing marks (not the ignition timing marks on the case) as well as the cam gear timing marks. Once you verify timing is dead-on, then it would be time to look into other things. If timing is dead on, try draining the fuel and replacing with new fuel. Gasoline isn't very stable, but something tells me 9 months isn't long enough to give you a complete no start.
 
#4 ·
I would almost think that you are 1 tooth off on timing, I've had a car jump 1 tooth and continue running (mind you it was running like crap) shut it down right away and then would not fire. Easiest way to check is pull it apart and check all the timing goods out.
 
#5 ·
If you can fully turn the engine by hand then you know that valves are not contacting the pistons. I would also double check the timing and for sure replace the gas.
 
#6 ·
Not if their already bent. When I bent my intake valves on a timing job, I would get no start, and back fire. I would check the marks first, then check compression to make sure your valves and stuff are good too
 
#9 ·
Like Isaac said, you still could have bent some valves. Do a compression test to be sure. It is a better sign than if you were turning the engine by hand and it would go clank and not move.
 
#10 ·
I have ran into similar situations where something built a nest in the exhaust and the car couldnt start, pull the front O2 sensor possibly and try to start it that way.
 
#11 ·
That's an interesting theory, but it has been in a garage the whole time. Hopefully that's not the case.

It does have DSMLink, and I forgot to reupload the tune. I wonder if that had anything to do with the backfire. But I've run the car without the tune before without problems. Just kept it out of boost.

The battery was also brand new too - I am not sure if maybe they don't come fully charged and the cranking might have killed it a bit which is why it's not cranking over. I don't know - I'll know for sure next Thursday. We are doing a compression test, getting good gas, and uploading the tune ect. Really hoping no bent valves.

Is it expensive to fix to have a shop replace the valves? Could I have possibly damaged the pistons. I mean- it didn't run for more than 3 seconds before it backfired and I shut it down.
 
#12 ·
A tooth or two wont bend valves on a stock 4g63, nor will it stop the car from starting generally. A shop replacing valves could add up quickly due to them wanting to get paid flat rate (book time) for the job which would probably call for quite a few hours of work, add in the time that the machine shop will charge when the shop sends the head out to them to have it gone through, lets hope its not a valve issue for right now. Did you damage the crank position sensor when you where in there?
 
#13 ·
ok. so we didn't have much time this Thursday to tear it all down. We turned the crank over by hand and could still feel the compression cycles - I am guessing that's still a good sign??? It also didn't sound unusual while we work turning it - no clanks or sounds of things being broken.

We didn't try to start it again, given the fact that we didn't have time to take the timing cover off, but we did take pictures of the cams lined up, and the notch on the fluidampr/crank pulley notch that is in line with the marks on the timing cover.

The reason why I don't think we are off on timing is because when the cams are lined up at TDC, the notch on the Crank Pulley is lined up as well. The Crank pulley can only go on one way, so I am assuming it's correct. Am I right to assume that timing is probably ok? Take a look at the pics. Any how, We are still tearing it down next week to make damn sure nothing jumped.
 

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#17 ·
Ok, so new problem. I didn't realize this at first because we were so focused on timing, but I was doing some troubleshooting yesterday, and found that I am not getting any fuel pressure when the key is in the on position.

I have a walbro 255 and AFPR. Usually I here it buzz right before I start the car - which is it pressurizing I am assuming. I am going to try to figure out how it's wired, and see if there's a fuse that needs to be replaced.

Here's the question - could that cause a backfire if that died during a startup? I remember when the car backfired - It smelled like a burning wires kind of smell. I had never had a car backfire before, and assumed that maybe that was just the smell of it.

SO now it seems that when the car backfired, either the fuse for the pump blew, or there's a short somewhere. I'll know more later.

At least that explains why it's not starting for now.
 
#18 ·
I would say pull your fuel line going to your fuel rail, and turn the key to see if fuel comes out. Check your mpi fuse aswell
 
#20 ·
Oh shit, do 2g's have a mpi fuse? On 1gs its on the positive battery terminal, the blue fuse, but have some1 else verify that, as I'm not familiar with 2gs
 
#21 ·
Ok so, the fuel Pump is rewired to the battery with it's own inline fuse, and is not blown. I also checked the fuse marked "Engine" 20A and that is ok too.

When I heard the backfire, I immediately smelled a burning wires kind of smell....so I am assuming something is up with wire, or relay. So trying that next. Ugh such PITA
 
#23 ·
The MPI fuse on a 2G is located behind the stereo in the dash to the bottom passenger side of the opening I believe. Do some more searching on it if you think that is it since there is a couple relays in the same spot. I remember from troubleshooting mine before, I searched and found out you could listen to it or feel for clicks after you turned the key or something like that to see if it was functioning. By the way when I was troubleshooting my problem ended up being the timing. Like already stated you could pull the line off the fuel rail and check for fuel flow. I also would pull the timing cover off the engine and check your crank timing mark, oil pump mark and cam gear marks just to be sure.
 
#24 ·
I haven't had much time to work on the car lately, but I do have a couple of guys helping out this Thursday to hopefully make some headway.

Out of curiousity, does the ECU disable the fuel pump if it thinks there's no gas in the tank? Because there really is barely any in the tank, and it's old - 8 months or so.

So far, I found the fuel pump relay that was rewired for the walboro 255 that the previous owner put in. It looks like he has it wired according to the vfaq. We are seeing voltage from the battery, the grounds appear to be ok, but we aren't getting anything from the ECU when the key is turned to the ON position. The relay also doesn't click - so this is why I am asking if it could possibly be disabled due to lack of gas. I could put gas in, but before I do, I just wanted to make sure, in case we need a new pump. Probably going to start with replacing the relay first - obvious small thing to do.

Any ideas? All fuses seem to be ok. Never found the MPI Fuse. Going to do some searching through the forums to see what I can dig up on it for the 2g.

Thanks for all your guys' help.
 
#26 ·
Update - Had an old friend come out to look at wiring ect. he brought a special tool that could apply 12v directly to the fuel pump to see if turns on, which it did thankfully. The relay was also functioning properly as well.

So basically it comes down to something stopping the ecu from telling the fuel pump to turn on - and we are guessing the crank sensor may have been damaged from the separating crank pulley.

So - i know you've all been telling me to check timing, but I didn't know if the fuel pump was related or not. I couldn't see why timing would make the fuel pump not turn on.

Anyhow - we will be going through and checking time, and swapping out the CAS and hope for the best! Hopefully I will be driving this thing by the end of the week!
 
#27 ·
Pulled the timing cover, and the timing was spot on; however we checked out the crank sensor, and it appears to be completely covered in melted plastic - from when the crank pulley separated and ate through the timing cover.

We just installed the new one, and just have to retension the timing belt since that had to be loosened to be put on the new sensor.

Hopefully that was just the issue, and all will be well by this thursday. The crank sensor being all messed up would explain why the fuel pump wouldn't turn on, right?
 
#29 ·
Pulled the timing cover, and the timing was spot on; however we checked out the crank sensor, and it appears to be completely covered in melted plastic - from when the crank pulley separated and ate through the timing cover.

We just installed the new one, and just have to retension the timing belt since that had to be loosened to be put on the new sensor.

Hopefully that was just the issue, and all will be well by this thursday.
Alright - well an update to an epic unforseen mess this has all become.

So - we replaced the old crank position sensor with the new one, and got timing all on properly. Put the key into the "On" Position, and the fuel pump doesn't prime. SO I am thinking shit - that wasn't the problem. So then we tried bumping the starter a little bit, and low and behold it primed.

Thought I was in the clear.....

We are now trying to start it with the alternator, crank pulley, and water pump not hooked up just to see if it would start - just so we didn't have to backtrak.

Go to start it, and nothing - "it sounds like it's not getting spark" is what one of my friends said, and the other said "it sounds like it doesn't have enough compression".

So.... now I am really scared. we go to turn the motor by hand at this point to see if timing is ok, and it's completely stuck and will not turn clock-wise. We then turned the motor slightly counter-clockwise and it sounded like something released, or something popped under the valve cover. My friend had his hand on top of the valve cover, and felt it as well.

After that, we were able to turn the motor by hand again..... which is unusual.

So at this point we are thinking broken valves, springs, ect. and just tore the valve cover off to get a look at what we were dealing with. Everything seemed to check out fine. Everything was tight and in place. We shined a flashlight into the cylinders, just to see what we could see, and didn't see anything unusal - although it wasn't like we could totally see, so I don't know 100%.

We weren't able to reproduce it locking up while turning it by hand again, and feared that trying to start would only cause more damage.

Could the noise have been a valve seat leaving a valve stuck open?

Why when we were turning the engine by hand did the fuel pump prime intermittenly? Could something be wrong with the Crank Trigger Plate - bearing in mind that the crank sensor was completely covered in melted plastic. I don't know where else that gunk could have gotten in to. or it normal? The key was left in the ON position mind you - so maybe it is normal.

Could the Crank Position sensor that I purchased be faulty?

I am at a loss at this point. This was a simple crank pulley removal, and replace that turned into this.

Any thoughts?
 
#31 ·
Well the pump will run anytime the ecu see's a signal from the cas, which when you werer turning it by hand would be a signal from the cas, so thats normal. I strongly urge you to check the position of the timing marks right from the get go at this point, it sounds like it is out of time and a valve is contacting a piston for some reason, maybe not, but just check for my own sanity, did you turn the crank backwards for any reason? even a little bit? if you could have then the cam timing could have jumped a tooth or more, all the more reason to check it!
 
#32 ·
yea, I'm telling you man - we checked timing before and after we tried starting it. Only after we started it this time, when we went to turn the motor by hand, it locked - we weren't able to turn it by hand at that point after trying to start it, until we slightly turned the motor back a hair - that's when we heard the small pop in the head - then it turned just fine, and everything was still lined up. Timing as far as we know - the whole time - was never off - at any point during all of this trouble shooting.

I had two brains on this for the whole summer. One who's a really good mechanic, and one who has full-on built 3-4 of these motors, so I know we had good experienced people working on this. I don't know what happened.
 
#33 ·
dropping the car off over at Innovative Tuning here in Buffalo for a leak down test and to check timing because we are completely at a loss at this point. So, we'll see what the hell happened. Probably going to have to drop $1000 for a head rebuild... I just know it.
 
#37 ·
uhhh.... the pulley was off... it has to be in order to even get to the timing belt.

*edit* oh you meant idler pulley.... Obviously we lost tension on the belt when we removed it, so we had to line up according to the timing marks. i mean the car ran fine with that pulley on there, and in fact if I could go back and do this all differently would not have replaced.