Backfiring thru TB

[B.O.B.]

Just finished my efi swap and trying to tune it a little and it is back firing through the TB. Could that just be a timing issue or the valves not adjusted right.

i did put new heads on and new cam, lower end is still stock 302 from 71 with about 79,000 miles on it. What do you guys think?

[Viperwolf1]

Could be a lot of things. Is it a regular backfire or does it only happen when you open the throttle?

Check the timing with a light and SPOUT unplugged. 10 BTDC is fine.

Check fuel pressure. About 39 psi is correct.

Check for codes.

[rtreads]

...check your upper intake!

Do you by chance have a typhoon intake???? ..ask me how I know to check that intake.

[B.O.B.]

I DON'T THINK I HAVE A TYPHOON INTAKE. JUST STOCK AS FAR AS I AM AWARE OF. WHAT IS THE DIFFERENCE.

[B.O.B.]

fuel pressure sitting at ~40 psi. Timing set @ 10 degrees btdc. Still backfiring and won't idle. PLEASE HELP. Or maybe someone will come on over for a little brew and some troubleshooting.

[Viperwolf1]

What parts went into the EFI mix? Part numbers from MAF, ECM, etc.

[Viperwolf1]

What is you throttle position sensor voltage set at? Using a digital multimeter, at idle, you should be as close to .98vdc as possible. Also, with someone in the vehicle, give it steady gas, disconnect the harness at the MAF, if there is no change, you have a bad Maf. Lemme know if ya dont know how to check the TPS.

TPS voltage doesn't need to be set to an exact value. It just needs to be in a range of about 0.8-1.2V. The system measures and determines the exact idle voltage at each startup.

[B.O.B.]

Everything came of a 91 gt mustang. A9L computer, stock tb (looks 55mm to me). I will try to get some of the other part #'s later. If I do not have vacuum hoses right would that cause this?

[Viperwolf1]

Everything came of a 91 gt mustang. A9L computer, stock tb (looks 55mm to me). I will try to get some of the other part #'s later. If I do not have vacuum hoses right would that cause this?

Yes.

[B.O.B.]

anybody know the correct vacuum hose diagram. tried to find one online but nothing really helps because of whole mustang intake / bronco retro fit.

[Viperwolf1]

There are only a few vac hoses needed. Fuel pressure regulator and PCV valve both get connected to the upper intake. Also a vent line from crankcase/valve cover needs to connect to filtered and metered air. All other vac ports should be blocked.

[GSMITH]

If you a older cam 15426378 ignition order you need to change the injector harness ingnition order to spray fuel at the right time. Just reminder double check spark plug wire order.

[Viperwolf1]

If you a older cam 15426378 ignition order you need to change the injector harness ingnition order to spray fuel at the right time. Just reminder double check spark plug wire order.

This is a bad idea. It will cause both O2 sensors to be reading from 2 of 4 wrong cylinders creating problems that cannot be fixed. Don't worry about injector firing order. If your cam (and ignition) firing order is 15426378 it will still run better than it ever did with a carb.

[GSMITH]

The mustangs are sequential fuel injection. This means the injector fires fuel with ignition timing.If it is the older firing order the injectors are not firing at the same time as the valve opening and spark timing. If injectors are firing at the wrong time fuel is being put into cylinder at the wrong time and will make it run poor. I change the order at the 10 pin plugs that are black and white.

[Viperwolf1]

The mustangs are sequential fuel injection. This means the injector fires fuel with ignition timing.If it is the older firing order the injectors are not firing at the same time as the valve opening and spark timing. If injectors are firing at the wrong time fuel is being put into cylinder at the wrong time and will make it run poor. I change the order at the 10 pin plugs that are black and white.

I might know a thing or two about mustang SEFI. Welcome aboard.

[GSMITH]

OK just trying to help. Thx

[B.O.B.]

Thanks Viper. Need to reconfigure the vacuum lines and should be good. Cross my fingers. I want to drive it again.

[B.O.B.]

Thanks GSMITH. I do have a new cam with the ho firing order. Welcome to the board.

[airbur]

Great thread.....will be doing something similar one of these days.

GSMITH.....in case you were wondering...Viper is the be-all-end-all EFI master (among most everything else Bronco:).....

http://classicbroncos.com/forums/showth ... write+book

[Viperwolf1]

Bob, shoot me a PM if you'd like me to take a look at it. I think we're in the same area of town.

[B.O.B.]

Great thread.....will be doing something similar one of these days.

GSMITH.....in case you were wondering...Viper is the be-all-end-all EFI master (among most everything else Bronco:).....

http://classicbroncos.com/forums/showth ... write+book

I read those posts on cb.com and they are hilarious.

[B.O.B.]

Still popping through tb. All vacuum lines hooked up correctly. Timing is set to 10 btdc with spout out. Anything else?