Backfiring woes

Vexxhoff · Jun 25, 2005

Hi there, I just installed a set of GT-40 "turbo-swirl" heads and a Cobra intake manifold on my 92 LX 5-speed. However, I can not get the car to idle so I can get it timed correctly.

Let me give you a little background on the car before I get into this. I bought the car about 2 months ago for $2500 and it needed a clutch cable and it had a couple of major exhaust leaks (passenger header and holes in the mufflers) I have since replaced the cat-back and put a Ford Racing clutch cable and quadrant in it. The car came with BBK shorty headers and some sort of under-drive pullies on the crank and the water pump (they are bright blue if that helps).

When I ripped in to the engine to replace the heads and the intake, the pistons looked good as did the side walls. I did not remove the timing chain because I was not going to do the cam at this time (want to try to keep it emmisions legal so I can take it back to the states when I PCS from England in a year) when I hooked everything back up I had to re-route some of the vacuum lines because the Cobra intake doesnt have the same fittings as the 5.0 HO intake (as I am sure you know) I also did not replace the rockers, lifter, or push rods (that might have been a mistake). I then re-installed the distributor and made sure that the rotor was pointing at the number one cylinder at TDC. Wehn I went to start it, it fired up...but was running like crap (backfiring or of the intake and would not idle). I have since found out that I put the wrong plugs in the car (Autolite 25...need Motorcraft AGSF-32C) and I have ordered the right plugs.

Now if this doesnt fix it I have only two options left that I would like some opinions on. Either the valves are not closing all the way (possible...but as far as I know the GT-40 heads are suposed to be bolt on and go) or someone either put a different cam in the car or took the time to change from a 5.0 EFI intake to a 5.0 HO intake before I got the car and I now have the firing order set-up incorrectly. So...what would you suggest that I do to get my stang back on the road?

Thanks in advance,

Timothy Fullagar

Vipersix · Jun 25, 2005

Sounds to me like you're 180 out on your timing. What method did you use to determine TDC (I hope you were looking at the #1 cylinder)? Depending on method it can be fairly easy to get in a hurry and stop exactly opposite of what you want and you will end up with an event just about exactly how you describe. I've never done that myself though... seriously...

Otherwise... by not changing the timing chain you really can't mess up the timing any. Another thing to look at is your firing order. You can get something like that from a wrong firing order and that has been known to happen.

The only other thing I can remotely think of is the rods and rockers. Did you use adjustable rockers? I assume you just pulled off everything from your old heads and put them on the new ones. If your rockers are set lower or the height is slightly smaller on your new heads your rods would be too long thus not closing the valves like you said. That would have a violent tendency to buck on the engine and you would hear a real neat backflow of your air sounding somewhat like a hiccup/cough.

Double check your TDC and I think you'll find your alternator is incorrectly installed. Your best bet is to borow or buy a positive stop and a degree wheel to get it as accurate as possible.

TheUser · Jun 25, 2005

Vipersix said:
I think you'll find your alternator is incorrectly installed. Your best bet is to borow or buy a positive stop and a degree wheel to get it as accurate as possible.

Did you mean cam? Not sure how you'd install an alternator incorrectly

Timothy,

I would suggest you stab your distributer again. 92's came w/ the HO motor, so if it had the HO intake, it's probably an HO motor.

To get it on TDC on the number one cyclinder, pull the plug, take a piece of paper towel and place it gently in the spark plug hole. Have a friend bump it over a little at a time until it pushes that paper towel out (make sure you have your coil wire disconnected at the time you do this so it does not attempt to start). Next, look on your harmonic balancer at the degrees. You want to get the timing pointer to 10-12* BTDC (to the right of 0). Stab your distributer with the number one pointing toward your number one plug wire. Tighten down the hold-down enough so the distributer won't move around on it's own, but light enough where you can still turn it yourself. If you have a timing light, it would come in really handy at this point - otherwise you're just timing by ear, which I think might be part of your problem). You want to get it where it runs well (10* is stock, some guys go to 14 - use whatever you like as long as it doesn't ping).

Are you sure the firing order is correct? Please, even if you're ABSOLUTELY POSITIVE it's correct, check it one more time. Firing order goes counter-clockwise 1-3-7-2-6-5-4-8 if you have an H.O. motor.

Good Luck

Vexxhoff · Jun 25, 2005

The way I gaged TDC was to have a friend stick his finger in the #1 cylinder spark plug hole and to rotate the motor by hand (with all the other spark plugs out)...and when his finger was pushed out of the hole we determined that to be TDC on the compression stroke. We checked it against the harmonic balancer markings and found that it showed at about 10 degrees BTDC...which is what I wanted. At that point I just used the harmonic balancer to judge TDC and re-stabbed the distributor to have the rotor pointing at the #1 cylinder. This, however, still did not work to get the motor to idle. As for the rockers and rods, yes, I just put the old ones back in (in the same place that they came out) and according to my Haynes manual only the very early Mustangs had adjutable rockers. So i didnt even try to adjust them, lined them up and torqued them down. I have checked the firing order 5 times and its right.....it just wont idle. Its too bad that I dont have the car right here in front of me or I would check the firing order again (the car is on base...about 10 miles from my house) The car does not use any water or oil that I can tell (no clouds of smoke or anything) but it does seem to get warm really quick....i found this after my 4 hour escapae of trying different small things to get the car to idle. Any other suggestions on this matter? Any and all help is appreciated.

Thanks
Timothy Fullagar

dstanggt50 · Jun 25, 2005

Vexxhoff said:
The way I gaged TDC was to have a friend stick his finger in the #1 cylinder spark plug hole and to rotate the motor by hand (with all the other spark plugs out)...and when his finger was pushed out of the hole we determined that to be TDC on the compression stroke. We checked it against the harmonic balancer markings and found that it showed at about 10 degrees BTDC...which is what I wanted. At that point I just used the harmonic balancer to judge TDC and re-stabbed the distributor to have the rotor pointing at the #1 cylinder. This, however, still did not work to get the motor to idle. As for the rockers and rods, yes, I just put the old ones back in (in the same place that they came out) and according to my Haynes manual only the very early Mustangs had adjutable rockers. So i didnt even try to adjust them, lined them up and torqued them down. I have checked the firing order 5 times and its right.....it just wont idle. Its too bad that I dont have the car right here in front of me or I would check the firing order again (the car is on base...about 10 miles from my house) The car does not use any water or oil that I can tell (no clouds of smoke or anything) but it does seem to get warm really quick....i found this after my 4 hour escapae of trying different small things to get the car to idle. Any other suggestions on this matter? Any and all help is appreciated.

Thanks
Timothy Fullagar

So, (might be reading this wrong, if I am , sorry) but you got on the compression stroke, and when you saw the balancer read 10, you just stabbed the distributor with the rotor pointing the #1, or did you put it back on tdc, then have the rotor point at #1? I would restab the distributor, and chk w/a timing light what your timing is.

Vexxhoff · Jun 25, 2005

dstanggt50 said:
So, (might be reading this wrong, if I am , sorry) but you got on the compression stroke, and when you saw the balancer read 10, you just stabbed the distributor with the rotor pointing the #1, or did you put it back on tdc, then have the rotor point at #1? I would restab the distributor, and chk w/a timing light what your timing is.

Sorry, I guess I should have explained that a bit better. I put the rotor on the #1 cylinder after I adjusted it to actual TDC. I have also been using a timing light....but it is a little hard to gadge it corrrectly because the car will not idle, but with keeping the RPMs up (about 1500-2000) the timing light says its pretty well dead on....but its a little hard to say that its right...because it is still back firing and sounding crappy.

Thanks,
Tim

Vipersix · Jun 25, 2005

You know... there could be some sort of extreme computer problem that is getting bad data and doesn't know exactly what to do to the engine making it go all wacky like that. There should be a spout connector near your MAF that will disable the computer from changing the timing. Not sure if you did that or not but if it's off enough that might cause an odd idle.

Vexxhoff · Jun 26, 2005

Vipersix said:
You know... there could be some sort of extreme computer problem that is getting bad data and doesn't know exactly what to do to the engine making it go all wacky like that. There should be a spout connector near your MAF that will disable the computer from changing the timing. Not sure if you did that or not but if it's off enough that might cause an odd idle.

I believe the connector you are talking about is right above the ignition module (its a little grey 2 pin jumper) and I have been trying to time it with that out.....however I did not have it out the first time I started the car....so the computer could be all screwed up at the moment. I will look for another one by the MAF and I will reset the computer to see if that helps. (unless Ford is different than all the other cars I have worked on I should just be able to disconnect the battery and pull the fuse right?) Thanks for all the suggestions guys, keep em coming if ya can...

Tim

Backfiring woes

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