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Topic: strange problem with my 5.0 (Read 772 times) previous topic - next topic

strange problem with my 5.0

i know this is a T-bird/Cougar forum but i have an 88 mustang gt that i did an engine swap to that i havent seen done befor and im having a lil problem with it. the original 5.0 HO blew on me and being 18 years old and makeing 8 bucks an hour i didnt have alot of money to spend on and exspensive high performance engine. i had an 86 crown vic that i used in a derby with a 5.0 but it wasnt HO. i swapped that in. i used the crown vic block and heads, i put the HO lower/upper intake manifolds on it. i used the HO fuel rail with the crown vic injectors, i swapped the computer, map sensor, and tps. i have hooker shorties, dual 3" with flowmasters, a 3" cold air intake, the throttle body/egr plate is 75mm, holly adjustable fuel pressure regulator(set to 45 psi), msd coil, cap and plugwires, and the emissions stuff and a/c is ripped off. now all that being said. the car runs great... most of the time. i can drive it all day long without a problem. but some times outta nowhere my car will just buck and vibrate and carry on like crazy. it useally happens cruiseing in 5th gear between 50-60. but it will do it in any gear at mostly lower rpms. if i get on it, it will usually go away but it will bog a little. if i push in the clutch it will go away instantly. and if i come to a stop the rpms will just bounce up and down from about 700 to 1200. ive tried swapping the map and tps, and that didnt help. i got the msd stuff incase of it being coil but that didnt help either. then i tried adjustable fuel pressure regulator and no help there either. im outta ideas and i was wondering if anyone else had this happen to them. its hard for me to figure out because it only happens when it wants to.  thanks...

strange problem with my 5.0

Reply #1 –
Few problems off the bat,fuel pressure sould be set at 39psi with the vacuum off and the 75mm tb is HUGE and is way to big for running an 86 engine the heads are just to restrictive,also 3" exaust is a ton over kill,your losing alot of torque there.
If your previous engine blew a rod then you should of swapped the heads,camshaft,intakes and injectors,this would have once again given you an HO motor and you could have used your ho ecm and would probably not be experiencing these problems.
Your crown vic engine had 150hp tops and your HO had 225,swapping only the intakes and tb will only net you like 160ish and would be a big drop in power.
Your problem lies in the throttlebody area,your trying to introduce to much air and are not suppling enough fuel(your engine does not need this)as it is now an SO motor(slow output).
Your ecm is trying to compensate for this as it does not understand the airflow increase,hence your fluctuating idle,5.0s already had a hunting idle and you've made it a ton worse with that TB.
If i where you i would pull the engine again, swap the cam,heads and get yourself a stock TB,this should solve all your problems.
On a side note when you change your tps you must set it to around .98 volts,just swapping it will not do.
Anything over .96-.98 and the ecm will think it's in off idle mode and be suppling more fuel than normal.
One last thing i just thought of,the crown vic was an automatic and you have now but it in front of a t5 manual.
Your ecm will be overly rich at idle,and again your engine does not need this.

strange problem with my 5.0

Reply #2 –
i know its a hell of a combination. it may not me the quickest stang out there but i was getting low 15's with it back in the fall after the engine swap. the thing that i cant figure out it is some days it runs great, the idle is fine, it wont buck at all, and its real smooth. but then sometimes outta nowhere it will just buck and jump. if im driving along about 55-60 and let off the gas it jerks the whole car around... feels like the whole rear axle is gunna fall off. it does the same thing when my foot is on the gas at times too. theres an 88 cougar 5.0 5 spd. at the local junk yard i might try useing the ecm from that.

strange problem with my 5.0

Reply #3 –
No 87-88 Cougars came from the factory with a 5-speed so if there's one in it, it was something somebody else did. If that car does indeed have a 5-speed in it, it probably has had the HO conversion as well and is using a 5-speed Mustang computer which you already have.

I think dominator hit the nail on the head mentioning the computer. You can use a manual computer in an automatic car but cannot use an automatic computer in a manual car. That's what I've heard, now I'm sure someone else here can clarify it for me.
 
Basically what you will need to do is convert the crown vic motor to an HO and just run with your existing Mustang computer.
 

strange problem with my 5.0

Reply #4 –
I did hit the nail on the head,the problems with his combo are due to the things he's changed on the so motor,That TB is way to big and i guarantee causing alot of problems as well as too much fuel pressure.
The auto computer can be used on a stick but not the other way around.
The 5 speed ecm has no enrichent at idle to compensate for the spinning of the big ball of fluid(torque convertor)and would cause intermitten stalling at idle.
The auto computer won't cause stalling but can cause a hunting idle due to not needing the enrichment at idle,causing the ecm to see a rich condition and trying to lean it out(ie:hunting idle).
On my wideband i can clearly see the ecm try to adapt when the idle is hunting(lean then rich,lean then rich)it trys to adjust to a perfect 14.7 to 1 at idle,if to lean or rich you get hunting idle.
Now i have the ability through my pms tuner to adjust for running huge 42lb injectors on my 5.0L when not in boost but you are very limited.
The only thing you can adjust is fuel pressure,and without a wideband this is very difficult to get right.
If i were you i would put the factory SO intake and TB back on,set the pressure to 39psi with the vac off(only to set,reinstall when set)then it should run alot better,the 5-10hp you get from the intake and TB are not worth the hassle and driveabilty problems.
With those restrictive e6se heads your running you are getting little to no benift to running those mods,hell i run around 450hp in my blown 5.0L and i'm only running a 70mm TB.
Or as fred said above,use the heads and camshaft from your old HO, then run the 5.0ho ecm and all your problems should be solved,and you'll be out of the pitifull 15s and back into the much more respectable low 14s where you belong.