ok here isthe deal i had problems with my Bronco and i fixed those ( had to replace the starter, battery, plugs, 1 plug wire, both battery cables and the solenoid) got the damn thing started then the gauges went bonkers,.. couldnt drive it without it dying out. .turns out a ground strap wasnt attached ( never was IMO since the motor was replaced) so I reattached it drive fine. except i noticed that a couple vacuum lines were broken. . fixed those,

Now .. here is what is wrong now, the thing accelerates fine up until 4th gear then it get sluggish as hell until i build up speed.

I replaced the fuel filter what now /> any Ideas ? plus it seems like it is out of time but you cant time a tfi-iv system can you ?

Help

 

We need more info on your bronco, like year, size motor, type of tranny things like this. go to your control panel and update your signature with some info so we know what you have. because this could be a result of many things

later

 

it is a 1987 Bronco, the motor was replaced with a new one back in 1997 when I bought it

<a href="http://motorhaven.autoanything.com/">302 </a>motor, with 36,000 miles on it

4 speed tranny, replaced the throw out bearing, pressure plate and clutch last summer

5.0 EFI.

 

what size <a href="http://service.bfast.com/bfast/click?bfmid=37919709&siteid=39251846">tires </a>are you running? you could have a clogged catylitic converter. those have been known to cause problems like that

 

I am currently working on a similiar problem. There are so many things that it can be. After a correct tune up of course, does it still do the same thing. I have been researching this same problem for over a year now. Changed O2 and MAP sensors, cleaned throttle body, checked all hoses for leaks, new fuel filter, every gosh darn fuel injection cleaner made. After a second look at spark plugs after changing, I noticed the rear cylinder on the driver side, forget which that one is, that the plugged appeared burned, ie no electode and oliy/carboned, so I replaced all again and it ran a lot better for a few days, now back to the way it was...that is seems the run fine with rpms higher than 2200, but lower than 2200 it is sluggish with no power....HELP...lol
John
90 Bronco, 302

 

to follow my last post... I have kicked around the idea of cutting the exhaust in front of the cat to see how the performance changes, if it does, I hope that that is the cause.

 

The fouled #8 plug is not uncommon. There are a couple of schools of thought on the problems that the 302 and 351's experience with the #8 cylinder. Oiling difficulties and/or excessive EGR gases causing the cylinder to run rich. EGR feeds the #8 cylinder first as I understand it.

Clogged/broken catalytic converter could be part of the problem.

EEC-IV systems can have the base timing set. You must warm the engine to op. temp.. Shut it off. Remove the SPOUT connector (small grey two pin "plug" that interrrupts signal from the ignition control module). Restart the engine with the connector removed. Set the timing according to specs. (usually 8-12 degrees BTDC but check a service manual to be sure). Shut it off again. Replace the connector. Restart the truck. Guys, if I missed something here, please, correct me.

As has been said, this could be and most likely is, a compound problem. I am still chasing a loping problem that occurs in the same RPM range. But I have an obvious "tick" at the #6 injector...going to replace all of 'em when I have the $$$.

I know part of my problem with the sluggishness at highway speeds is the fact that I still have stock 3.55 rear end gears on 33" tires. Throws the 302 well below its power band of 2500-2800 rpms once the E4OD drops into OD.

 

Greystreak...sounds like you have a similiar problem. Not that it is a good thing, but it helps others with similiar problems. Timing was done as you said with no change. would a picture of the spark plug help?
John

 

Kilted,

Got a pretty good idea what it may have looked like. I had a Bosch Platinum do something like this in my #8 cylinder as well. All this has happened to a 302 that is less than two years old. the original engine in mine had blown a hole in the #8 cylinder which was obviously letting oiling into the combustion chamber and slowly killing the whole motor. One of the guys, Pig Farmer maybe, recently posted something that he did in an attempt to reduce EGR flow to that cylinder. I don't recall exactly what it was or how he did it. I have gotten my problem narrowed down to a fuel injector and/or the necessity to change rear end gearing.

I initially thought maybe I was dealing with a transmission problem because of the shuddering the truck would do. But I replaced fluid and filter on a rebuilt E4OD and it did little to improve the situation.

 

you mention shuddering. At what rpm range does this occur? Is it rpm range right before the tranny downshifts to next lower gear?

 

Any idea what a good method for checking for a plugged converter is short of cutting the exhaust work? I've heard that if vacuum drops off for the first minute or so after starting up that there's an exhaust restriction. Any thoughts?

 

Kilted,

Yes, just before the upshift to OD most of the time. Feels almost like its starving for fuel at the low end of the power band. Pulling codes from the computer might yield something but it hasn't done much for me in chasing this problem. Evidently the computer doesn't think there is anything too far out of whack. Someone suggested replacing the knock sensor at one time. Since the knock sensor tells the computer to alter fuel mixture to compensate for knock, if it fails or isn't working properly, the computer may run a "default" mixture since it is getting no reading from the sensor. That "default" may be too lean under acceleration but will deter the possibility of more damaging "knock and ping". I have yet to crawl back behind the intake to swap the sensor. Sorry I forgot to mention this point before. I had forgotten about it until the wife saw me typing and asked if I had ever "fixed that stupid sensor that you have been grumbling about". But thats why I'm married. Her memory is better than mine.

 

I will look at the knock sensor tomorrow also...Thanks for the idea. Can anyone add to the question just posted in this thread about testing the cat short of cutting the pipe before it?

 

A couple of Cat tests

Pull the O2 sensor out and go for a drive, see if it helps

A vacuum gauge that also has a fuel pressure gauge, or a pressure gauge that has a 1 to 10 pound scale, may also assist you in diagnosing a clogged exhaust.


If you connect the gauge upstream of the converter, either in an emission test port or by fashioning an adapter in the oxygen sensor hole, you can measure the exhaust backpressure. A general rule of thumb is no more than 1.5 pounds of backpressure. Another test, using a vacuum gauge, is to measure the engine vacuum at curb idle and at 1600 RPM. If engine vacuum is 21 inches at curb idle and 15 inches at 1600 RPM then there is a good possibility your catalytic converter needs to be replaced.

 

Thanks mgillete...will take a look at those ideas in the next few days..