ok heres my long story... my 1988 bronco with 302 efi.

i was driving along one day and then all of a sudden my truck was accelerating rather slowly. i finaly got up to the speed limit and just for the heck of it, i floored it. instead of going faster, it slowed down, almost like it was bogging down. so i let off the gas and kept speed. gave it a little bit more gas and accelerated a tiny bit. so i floored it again and saw some nasty lookin smoke come out of my exhaust. it looked blackish blue but it was spittin something fierce. well i came up to a stoplight and then it stalled on me as i began to stop. cranked it back up and floored it just to keep it running, while i did this i had it in neutral. so i threw it in gear and slowly turned and slowly accelerated. i finally got to where i was going and stoped and left my truck running. well it was acting weird, it was reving all the way from 500 to 1200 rpms, or so i remember. but it would oscilate between those ranges. like it was fixing to stall. then it started to run fine. and again it started to oscilate. well sat there and reved it with the butterfly just to see if i could notice anything, of course i couldn't. still spitting fierce blackish blue (basically dark) smoke. ive been told that this kind of smoke is because of burning too much fuel, too rich. i was able to get it home and park it there but it was one heck of a time tryin to get it there. point in case, truck no longer runs. had it towed to a mechanic after i checked for any vacuum leaks. they ran it on the computer and found no compression in 7 and 8. sucks big time. then he was tellin me that Ford has a problem with somethin called cross arcing so pistons are firing when they're not supposed to. he explained like someone with a pacemaker and how they're not supposed to go near a microwave. and something like it would melt holes in my pistions if this was the case. well im planning to replace my engine so i was pulling my motor out today and then i took off the heads and saw no holes or any sign of trouble. i checked the valves and all are lifting and closing. looked for broken shafts all i found was carbon build up. DOES ANYONE HAVE ANY INFO ON THIS??? I NEED HELP!!!

 

sounds fishy to me .. never heard of 'cross arcing' pistons. of course anything is possible ...

on the other hand, if it's firing out of sequence then we have a timing problem. and why 7 and 8 are dead, could be well worn rings, but i couldn't tell you for sure.

but if you've torn it down that far, then take time to check the timing chain.

the blackish-blue smoke could have been fuel build up from the flooring of the pedal and was nothing but a seriously rich fuel burn. just like running an over enriched carburator.

**
ambrose

 

did this problem just start or has it been slowly working up to it?did you check the fuel pressure regulator?the regulator operates on vacumn. it regulates how much fuel pressure is in the fuel rail and sends the excess back to the tank. when you floor the truck itwould lower vacumn and the regulator would close and give you more fuel at the fuel rail when you come off the gas vacumn would increase and the regulator would open and send fuel back to the tank. black smoke is way rich and the only thing that regulates the amount of fuel is the fuel pressure regulator .just a thought.

 

The cross-arcing issue isn't because of the pistons, it because the spark plug wires can induce enough voltage into each other to cause the wrong plug to fire. It's usually caused by having the wires run too close to each other in a straight line. Crossing at 90 degree angles, or keeping them farther apart eliminates the problem. Of course that won't cause a no compression issue. If there was no compression, then there has to be a problem somewhere. Did the head gasket look OK?

 

yes the headgasket was fine.

another thing, the mechanic i sent it to said that he did everything he could get the timing right but couldnt do it.

it just all of a sudden started doing this. and the black smoke only came out when i gave i floored it.

no i didnt check the fuel pressure regulator, i wouldnt know where to or what to look for.

 

The fuel pressure regulator sits on the left rear of the fuel rail. You'll find it back behind the coil; it's a silver-colored object that looks like a miniature Altoids canister held down by three allen-head bolts, and it has a vacuum line coming out the top. But, it sounds like it's a bit late to be checking that, so this is all for future reference.

 

if the mechanic couldnt get the motor timed properly , you may be needing a new timing chain set. with the heads off turn the crank so its at TDC . if the mark lines up but the piston is not at tdc then you have a bad timing chain. pull the water pump and timing cover for any visable signs of wear. you might be suprised what you find. also when you turn the crank with the heads off look at the cylinder walls on 7 & 8 . if the rings are gone you might see signs of wear on the walls. sorry to hear your mis fortune.

time to build a stroker !!!!

later

 

I agree with the fuel pressure regulator. My wife had a Silverado and it did the exact same thing you described. She didn't have smoke puffing out until I floored it and the truck surged when I did. After a few days of driving it carefully it got to the point were it would only go if you touched the gas with a hair...any more pressure would stall the motor, and it would backfire as well.

Took it to the local shop and sure enough, fuel press reg! Runs like new now. I thought it was a clogged fuel filter, but it wasn't. But atleast it got changed during the process of elimination.

good luck

 

I agree that if the guy can't get it timed he is either incompetent, or the timing chain is bad or has jumped. However, a bad timing chain would not make the timing mark on the balancer and the piston not line up at TDC. The balancer is bolted to the crank, and unless the crank is twisted or the balancer is somehow installed worng, it will always line up with the piston no matter what's going on with the timing chain. Now, you can check to make sure the chain is OK by turning the engine so the timing mark is at TDC and making sure the rotor is pointed at the #1 post in the dist. cap. (It could be off 180 degrees because of the 2 to 1 rotation ratio of the crank to cam, so if it is just turn the engine over one more time.)

 

would the fuel pressure regulator cause there to be no compression? if there's no compression then that sounds like something mechanical, and it looks like a mini altoid can? i looked and i didnt see anything that looks like a mini can but i saw a black plastic setup on the driver side of the intake manifold with three wire plugged into it so i dont know if thats what ur talking about. if im wrong can u please be a little more specific. I LOVE MY BRONCO AND WANT IT BACK SOOOOOON!!!!

 

No; if you have no compression, you have a mechanical problem and the fuel pressure regulator is of little import at this point. It's a small silver thing that has only a single vacuum line going into it, and it sits on the fuel rail near the firewall on the driver's side.

I think that the fuel pressure regulator was brought up in an earlier post as a problem that may have contributed to a mechanical failure. At this point, it seems like you need to take care of the bottom end before you start worrying about fuel delivery again. Sorry to hear about the turn things have taken.

 

At this point, it seems like you need to take care of the bottom end before you start worrying about fuel delivery again.

i think im confused, what do u mean by "bottom end"?

 

The engine block and everything inside it.

As opposed to the "top end", which is the heads, intakes, distributor, etc.