Help With Lean Pop

[gtcobra302]

I have a 1989 mustang Gt. It has developed a lean pop at low rpms when under load. It kind of sounds like it is back firing through the intake manifold. Just when cruising at lower rpm's, if you get on it it goes on by it at about 2500 rpm's. any ideas would be greatly appreciated. This is what is on it in that department. Trick flow intake manifold, 70 mm t-body, 73 mm mass air, 24 lb injectors, fuel pressure at 40 psi, ported and polished gt40 heads, tps at .98, 255 lph fuel pump.
thanks

 

[jrichker]

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

 

[18mustangs]

I have a 1989 mustang Gt. It has developed a lean pop at low rpms when under load. It kind of sounds like it is back firing through the intake manifold. Just when cruising at lower rpm's, if you get on it it goes on by it at about 2500 rpm's. any ideas would be greatly appreciated. This is what is on it in that department. Trick flow intake manifold, 70 mm t-body, 73 mm mass air, 24 lb injectors, fuel pressure at 40 psi, ported and polished gt40 heads, tps at .98, 255 lph fuel pump.
thanks

Have you deleted EGR, and if you did delete EGR did you turn it off in the computer? How new are your sensors, specifically the ECT and ACT sensors? Also clean the MAF for good measure and maybe the ACT as well. If you haven't given the car a good tune up in a while you might want to replace the fuel filter, check your cap, rotar for corrosion and your plugs..just the basic stuff in case it is pinging instead of a back fire. Also 02 sensors can cause the ping or backfire if they're not working properly. Check the codes and see what comes up. With the setup that you have I'd recommend lowering the fuel pressure as well at least back to stock (if 40 PSI is vacuum on and you have an AFPR) or perhaps a little lower.
Tim