Help! Backfiring and loss of power

[spuckie]

Looking for any insight or help someone can offer...sorry about the length

I have an 88 LX Conv 5.0 automatic that's I've had for 2 years...

Car started backfiring a month ago. Took it in thinking a tuneup would fix it. Took it to a friend of mine who owns a shop (he's driven mustangs for about 10 years, so I figured he was a good choice) and he tuned it up and said it was driving great. Couple of days later, it starts backfiring again. This would happen usually around 50mph when I tried to take off. Took it back in and he made some adjustments and said, once again, it was fine. Couple of days later, same thing. Now it seems worse. Backfiring at all speeds when I try to go faster. It was at this point that I'd have to enter a highway at a slow speed and letting it build up instead of taking off. I was in a mustang driving like an old man.

Gave it back to him again. He made some adjustments yet again and told me it wasn't shifting properly. He says he brought it to a tranny guy he knows and they went over it. He also tells me that I'm gonna need a tranny sooner or later.

I've now had the car back for a week. Overdrive slips like crazy. So much that I hardly use it. I couldn't go over 65 on the highway yesterday afternoon. Last night, it seemed like 55 was the limit. It also seems to shift from 1st to 3rd. If I manually shift it, it will go into 2, but only if I delay shifting it. Also, after building up speed a bit (to about 35-40), if I give a good push to the gas pedal, the car does nothing...no backfire...no engine revving...nothing! I'm wondering where the gas is going if I do this. I've held it like this for up to five seconds and no increase in power or backfire.

The car is also backfiring like mad still!

My mechanic...my all knowing mustang mechanic...says it's got to be related to the transmission. That because the car is not shifting correctly, it's causing all the other problems.

My main concern is investing the money in getting another transmission, only to get it back and have it still backfire on me or have this total lack of power.

I don't really know what to do.

Has anyone encountered a problem like this or heard of it??

If you'd like, you can email me at jspag71@aol.com.

Once again, sorry for the length, but I'm at my wits end!

[84LX89GT]

I'm sorry to hear your car woes, it's never pleasant to have that many problems.
Did it sound like it was backfiring through the exhaust or through the intake?
There's alot of things that may cause a backfire/misfiring, so i'll list as many things as i can think of. unfortunately the only way to single things like this is out step by step diagnosis.

It sounds like no matter what your transmission is shot if it's actually slipping. Although when you have drivability problems that can cause erratic shifting, but your trans problems sound deeper than just shift scheduling.

Lean (intake) backfire:
The MAP sensor (manifold absolute pressure) can cause a lean misfire especially under load because all engine calculations are based off of that sensor and it measures air density, they can fail and read that you're at say for example 30,000 feet when you're at sea level, which air is thinner so you need less fuel - causing the engine to run lean. Some ford dealerships have a diagnostic tool called a SBDS that can test MAP sensors, or you can read the frequency being generated by the sensor by backprobing the connector and measuring with a multimeter. It should read around 159 Hertz around sea level.
Also if it's a lean misfire/backfire, fuel pressure is vital and if it drops under load and isn't able to supply the proper amount of fuel, this could be a result of a plugged fuel filter, bad fuel pump, bad fuel pressure regulator or kinked line.
Is the engine running hot at all? Excessive heat in the intake manifold/head can cause the air/fuel to light before it gets in the combustion chamber.

Rich (exhaust) backfire:
A backpressure sensor could be used to test if the catalytic converters are plugged. If the converter(s) are plugged it will kill power especially under high load and cause exhaust to push against outgoing exhaust eventually pushing it back in the cylinder/intake manifold when the intake overlap begins.
If you're engine is running really rich it will dump fuel into the catalytic converters and they will light there and can cause backfiring in the exhaust, and eventually melt the catalytic converters by super heating them.
To test for it running really rich a fuel pressure test is the first thing i'd do (it's one of the first tests that should be done since it's the least intrusive.) If fuel pressure is really high the processor will be unable to comprensate for the extra fuel by cutting back fuel trim and your car will run rich. High fuel pressure can be caused by a bad fuel pressure regulator or kinked return line.
Another test that can be done is block off the fuel return line and measure fuel pressure leak down to see if any of the injectors are stuck open dumping fuel.
Has your mechanic done any diagnostic scan tool tests to see what the processor is reading, diagnostic trouble codes help alot in determining the possible cause.
These are the biggest things i can think of and i hope it helps you out, good luck.