sounds like u have a valve hanging open and not closing properly.

 

Try bumping up the timing alittle

 

ditto, timing causes backfire through the intake.

 

The motor is fresh from top to bottom. I rebuild the motor including rod, main bearings, new valve springs, seals, and retianers, with a 3 angel valve job, they are iron gt40 heads that are ported and polished. They only have maybe 1000 miles on them. I did it a couple years ago then went to school and it sat, getting driven every couple monts or so. I have the timing at 10 degrees for the 100 shot of nitrous that is on it and is rarely used. Is it safe to give it anymore timing?

 

An intake vaccum leak can cause that easily. Check the gasket seal between the lower intake manifold and the cylinder head by spraying carb or throttle body cleaner at the line where they meet with the engine running. If the idle suddenly changes (ramps up), you've found a leak.

 

Popping through the intake is an indication of a lean condition or too low of timing.

 

Awesome thanks guys, as soon as I get home Ill try those things and report back.

 

I had the same problem with my TFS kit (24lbs) when I was N/A.... I tried everything, until someone told me to clean the MAF and that did the trick.

Here's my post from 05 with my checklist and post #15 did the trick.

http://forums.corral.net/forums/showthread.php?t=661457

 

I had the exact same problem with mine and it turned out I blew out one of my intake gaskets.

 

Okay so I put fuel pressure at 44lbs with the line off and timing at 14 degrees, but to no avail. I am going to look for a blown intake gasket, anything else it could be. It seems to go away after about 5 minutes of driving.

 

it could be a slow o2 sensor

 

Check you fuel filter as well. Mine does that when the filter starts to clog.....

 

My hesitation and intake manifold backfire go away when the car warms up, usually about 5 minutes into the dirve. What does that mean?

 

Same

I have the exact same issue. :curses:

Only under load, and only when cold (first 5 minutes or so) I get a moment of hesitation when I hit the gas, then a pop out of the intake, then she takes off. After a few minutes of driving, as the engine gets up to temp it pretty much goes away (once in awhile it will happen when warm, but its rare) The car pulls hard otherwise and does not smoke.

I currently have no computer codes.

I have a Walbro 190 pump I just put in (no difference) and rebuilt and bench flow tested OEM 19lb injectors, new Ford wires, new Motorcraft plugs(gapped properly), new upper and lower intake gaskets, a few new vac lines, new fuel filter, IAC, fuel pressure is currently set to 43psi with vac line off and thumb over (backfire seems less pronounced the higher the fuel pressure I've tried 38-46 or PSI and noticed its slightly better with more pressure). New ECT, ACT and Motorcraft O2 sensors. I have a pretty steady vac reading with no sweeping.

I have swapped other known good parts with a buddy too: TFI, coil, distributor, EGR, MAF and a handful of other items.

Timing is currently at 12 deg with SPOUT out, I have also tried 10-15.

My timing does not jump around at idle, but I do hear some timing chain noise at low rpms. I have also checked for timing chain slop by turning the crank back with a breaker bar, then forward and watching the dizzy. There is no slop to speak of.

My best guess is I have an intake valve or two that is not seating properly.
My car currently has 90,000 miles on it.

 

I had the same problem on a 5.0L I was working on and solved it by bumping up the fuel pressure (to 45psi) and running it with the vac line off. I know it's not the right way to do it but it worked lol

 

I had this issue last year when I put the engine back in mine, drive fine for 2-3 min. then hesitate and pop for a minute then it cleared up. I checked every sensor/ vac leak nothing.
I swapped my O2 sensor connectors left and right and the problem was gone! Drives fine now, Hope this helps you

 

I am not a fuel injection expert...but here is what I understand. When the engine is cold it is "open loop" operation. That is to say that the computer is controlling things from a map that is contained in the computer...it is not using inputs from the O2 sensors. Once the engine warms up the O2 sensors come into play and are used to trim the Air/Fuel ratio. Having played (aka big pain in the a$$) with Fuel Injectors, Mass Air Meter, sample tubes, etc. my guess is that the mapping in the stock computer is off a bit when its cold for your current set up. If the suggestions above don't remidy things there are a couple of solutions that I would recommend. Put the 19lb injectors and Mass Air Meter back in. If this corrects the problem there is your answer. You could also take the car to a tuner in its current form, and get it dyno tuned. That's a bit pricey...like $650 or so for the chip and the dyno pulls. I have also heard of people mail ordering chips for their set ups...can't recommend it as I never did it. Good luck.

 

I had the exact same problem on my 87 GT. It turned out to be the computer. I too got no codes when I should of had a 45 and 46 since I had removed the air injection.

 

i know its an old thread....but I was wondering if you ever figured it out?