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96 351w supercharged problems

5K views 43 replies 11 participants last post by  Nemean 
#1 ·
Sup guys,
Well this is my brothers truck. He bought it has a power dyne supercharger on it. It ran great for awhile and started to buck around 30 mph 3rd gear. I took it to my local mechanic and they thought it was fuel injectors since they were stock and it was supercharged. Well we called a guy in town that tunes so,he said its needs 42 lb injectors so I get them and put them in and it would start just ran like crap. Well we took it to him he tuned it says it has a good tune and it would idle great you could rev up and dent things would turn up....well when u go to put in gear and get on it will shut right off....we replaced module coil pack and distributor ....none of it has fixed it and it also has great fuel pressure...anyone that's knows these computers or trucks....we need help don't understand what goin on....sry this is so long just running out of options...thanks any help is appreciated

Jason
 
#2 ·
i have experience with forced induction and I can say that one really had to know what they are doing to be able to make it work right, or have the money to pay someone who does. What your bro is trying to make work is not a trivial endevour.
 
#3 ·
Ok first of all you need a wideband on that thing or you are just guessing. Take off the belt and floor it. Does it fall on its face? What are the plugs gapped at? Did you remove the FMU when you went with larger injectors?
 
#4 ·
If it's hard to start and runs bad then he didn't adjust for the 42's right. Sounds like its dumping too much fuel. I'd throw a 12:1 FMU and the 19# injectors back in there.
 
#7 ·
If you have 42's and a tune there is absolutely no need for an FMU. If the tuner looked at it and didn't notice it then he sucks bad and I wouldn't use his tune. As soon as you hit even a little boost you are waaaaay flooding the engine with that FMU. Options.....

Reinstall the stock 19's and keep the FMU. Lets hope it's a 12:1 FMU disk.
Or
Remove FMU, have the tuner decrease the injector minimum pulse width during crank mode.
 
#8 ·
A few questions:

What did the "tuner" use to tune it? Did he actually change the computer settings?

A 96 is OBDII, do you have a check engine light? Engine codes if you do?

This is a Mass Air truck right? Normally the mass air is calibrated for a particular size injectors, was there any change to the mass air meter?

And you say it ran great at one time, how long did that last? Days, weeks, months?
 
#9 ·
Months it ran fine...he actually has a dyno and computer software not sure what though....no engine codes......no change to mass air.....it ran great before it started bucking and we changed injectors amd tuned and wont run when u go to get on it. Could too much fuel from fmu be making the computer shut it down
 
#10 ·
It should be throwing codes and a cell. These rigs will usually tell you what's wrong. You can, in some cases tune around a faulty part, but you shouldn't. The engine has to be mechanically sound and all the electronics working right before a tune.

Sound like something with the EEC, ignition, or even a relay if it just shuts down.

I tried a Powerdyne on a 1990 with speed density. It never ran to it's potential and once I pushed=it up to 9lbs of boost I lost a head gasket from predentonation. I had a bunch of problems with it till I did a mass air conversion, added a higher volume fuel pump, larger injectors, and a good tune with a Tweecer. Anything less thana good tune with a custom chip, Tweecer or Moates tuner is a band-aid!

The problem came before the tune, something else is wrong and the tuner should have caught that.

How much boost?

Did your tuner burn a chip, make a custom tune and install it?
 
#13 ·
Now we are getting somewhere. So when you floor it the Bronco dies completely and you have to restart it? This only happens at wot? What about part throttle but using half like trying to go 90mph?. I would suspect a bad tps or MAF Meter.

Why did the tuner leave the FMU hooked up with 42's? What MAF meter does it have? Can you list all the mods?

Since the tuner couldn't go to full throttle he really tuned almost nothing. I would resolve this and ask for another tune.
 
#14 ·
Well i went there yesterday to check it out they put the new distributor in and pulled it out and went to go not full throttle like 1/4 throttle and dies like u turned the key off....so i jump in it and go in reverse it idles fine and revved it to about 3500 no problems. Put it in drive and shut off...started back and put in drive was good and gave it a bump of gas and it shut off...will sit and idle all day but once under load nope. As far as maf its the oem one.....and i always wondered what the fmu was and finally figured out it had one when he bought it....as far as mods just injectors power dyne and headers . Its just super weird cause it never did what it was doin....the only thing it did before was kinda the same thing it woulf shut off randomly at like say a light or whatever but u could go 1 day or 7 without it doing it.....and i dont want him to keep sinking money in it if they cant figure it out but we just cant take it because of the tune on it after we already put time into the injectors....
But 42s do seem very drastic for 5 lbs of boost.....and thanks guys for the help i know alot of u know a bunch about these motors....
 
#15 ·
is the blow off valve working properly? get that fmu out of there, you didnt really say if you did that or not.

only 5lbs of boost? perhaps those 42's are to big as well? I also didnt think the stock fuel pump in our broncos could handle forced induction fuel needs and thats why folks have upgraded to the walbro pump???
 
#16 ·
Fuel pressure needs to be verified first. First when u rev it at idle and again when it stalls.
 
#22 ·
if it were for my friend I would put the 19's back in and hook back up the FMU. They will take you all the way up to 12#'s of boost with a good 255 inline pump and a 190 in the tank. Stock tune, no chip, pull the spout and set the timing to 16º. Leave the spout out. Then buy an MSD with the timing retard. Set the base timing to 10º and retard dial to 1.25º's per pound of boost. Always run 93 and call it a day.
 
#25 ·
The spout is next to the TFI module. Unplugging the spout takes the computer control out of the timing. Pull it and set to 16 degrees until you get a BTM. Do not reinstall it until timing is back to 10 degrees later down the road. Don't forget to remove any chip the tuner put in the J3 port.
 
#26 ·
This was already mentioned by kemicalburns but I didn't see any response.

Have you verified the fuel pump is maintaining Adequate pressure at WOT?

I had this same problem with a SC 4.6L SVT Thunderbird I had.
I threw all kinds of parts at it until we finally threw a wide band A/F meter on it and had it dynoed to figure out what was going on.

It turned out to be the 255lph fuel pump wasn't keeping enough pressure at WOT. Replaced the fuel pump and the thing ran like a raped ape after that!

Since you are OBDII you shouldn't require any other programming adds so don't waste your money there.

I am having a tendency to agree with a few others here that you may not be using the right shop if they can't tune this thing. They should be able to program your EEC to do pretty much anything you desire.

We did go with 42lb injectors in it. Ran great afterwards but since we discovered the problem post injector change I suspect the 35lb may have been adequate. I didn't want to change back at that point just to find out.

Keep us posted, you have an awesome Bronco there if you don't give up on it.
:beer
 
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