Hi guys I'm having a problem car is 86 trans am with 305 tpi it backfires in park only which is strange fine in drive. What I noticed is that the oil pressure on e guage drops in conjunction with the rpm drop from the back fire. You can literally feel e backfire travel underneathe you while I'm waiting in park. I also have a hard time starting the car after its driven. Started after I threw in the Bosch iii injectors and ad fuel pressure reg ... Not the backfiring, the hard starting.

 

You probably got your wires mixed up, about 3 mins ago I read a post on this same thing, guy mixed up wire's one and 3.

Could also be a hole in your exhaust!

 

I may be wrong here, but if that was the case it would be worse in gear, itd feel much weaker and would be louder backfiring in gear too. If its ok in gear just not right in park, i dont think that would be it. It definetly doesnt hurt anything to double check tho! Also make sure all connections are good and theres no corrosion or rust on any.

I think what i would do is check fuel pressure first, make sure the fp regulator is adjusted correctly. Maybe adjust it some and see if it helps any. Even though theyre new, Id ohm out the inj's too, just to rule that out.

Timing can cause these problems too.

Are the new injectors a bigger #?

The hard starting when hot is a very common problem with these cars due to the Y pipe being so close to the starter soliniod.

 

Double checked wires, fine. Had the timing done when my mechanic was diagnosing a stalling issue (turned out to be the prom). He said when I changed the cap and rotor I didnt do the timing right so it was off. He fixed it. Had an old hypertech chip I gave it to him and it fixed everything but the hard starting. Fuel pressure I checked with a guage a solid 42.5, these are the bosch iii 19 lb injectors. The prom burned out but the car was backfiring from the factory when new. When I have it in drive you could never tell it had the issue. It's only in park and after is has been run 10-15min. Idk if this is normal or not but a plume of white smoke comes out on the cold start up smells like burnt chemicals. I was thinking the ignition coil or the spark plug wires are getting hot but I can't see anything. The mechanic raped me for 300 for all that work so I'm broke right now. Gotta do the work myself

 

Im a little confused, to change the cap and rotor doesnt affect timing.... Unless you pulled the distributor out, or tried re-timing it and did it wrong. If you did the firing order wrong when hooking the wires up to the new cap, i could understand that tho.

The smoke, its probably bad valve seals allowing oil to go thru, into the combustion chamber. My car does it too, its very common for these cars. Only way to fix it (that i know of) is a rebuild and replacing the seals.

How many lbs of vacuum do you have?

 

He said that the metal piece wasn't touching right and that the timing was a bit off, I didn't change any of that. The wires were on right I had my mechanic friend look at them and he said it was good. Now today it did it a bit in park waiting for my gf, then after I went on the highway and a little stop light race, it went away. only once in a while it would do it in park. How bad is the re build for those seals? Also, is it normal when you have the ac on and fan on for the car to drop down to 500 rpm after stopping and then creep back up?

 

Im not quite sure what your asking, just because of how its worded lol but, just to cover my bases ill explain for both possible answers. You cant get the seals rebuilt, im not sure if thats what you were asking. You have to replace them, and to do this you have to tear into the engine (remove intake, exhaust headers/manifolds, heads,ect) and get the heads cleaned up/rebuilt. Its when the heads are off and in the machine shop that they can put the new valve seals in. Its not a cheap or easy process, so to go thru all that just for the valve seals is a bit overkill imo. If you plan on doing a rebuild down the road anyways, just put it off until then, or do the rebuild now if it really bothers you lol. but it doesnt really hurt anything, just make sure you kep an eye on your oil level. You can also buy smokeless motor oil, so even though the problem is still there, you wont see the smoke.

As far as the ac question goes, i really cant answer that with 100% positivity. My cars ac needs to be recharged, and i havent gotten around to it yet. I ususally ride around with windows down and maybe even t-tops out I could see that though, these cars idle very low to begin with. the addition strain of the ac system could feasble make it idle a bit lower for a few seconds until the computer raises the idle back up. This could also indicate improper timing though i suppose, if that isnt normal.

 

Oh I see, as long as it doesn't hurt the engine I'm fine with it. Strange how the backfiring comes and goes. I was asking about the whole rebuild process which you answered perfectly. With the hypertech chip in the cars fans turn on at 175 and off at 160. So it's always on. Its just that i'm paranoid about it since the old prom was burnt and the car kept stalling at every light. But it seems like my dads tahoe 2012 does it to, just the only thing is in the ta you can feel the engine and hear it drop down then up. Don't you get sunburn with tops off? I get burnt to a crisp when I do parades and shows. Ah one more question. I have a grinding noise when I turn the wheel from a stop (only stop) and when I turn slowly like moving around in a parking lot at like 10 mph the steering wheel shakes and sometimes snaps can be heard from the front end. What could this be? Thank you for all your help I really appreciate it I know this is a bit off topic too. Ah one more thing, I heard of a TSB for the 1986 proms that there was a replacement, do you know where I can find these replacement proms?