Idle/accel problems

little5.0 · Aug 28, 2010

I have an 88 gt 5.0, stock block/head, just changed out the intake for a ford racing cobra GT40 intake, 21lb injectors and a cam fuel pressure regulator. I'm having problems with it idleing right and when you accel it start backfireing and bucking, also has lost power. Ive reset motor to TDC and reset the timing and ive tried advancing and retarding the timing but nothing just yet. any help please respond

jrichker · Aug 28, 2010

You have 21 LB injectors? Have you done a Mass Air Conversion? If not, there is your problem. Do you also have an aftermarket MAF calibrated to match the injectors or custom tune to match the injectors to the computer? Stock injectors are tan or orange 19 lb units.

Diagrams courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 86-95 5.0 Mustang wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 94-95 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

Vacuum Diagram 87-93 Mustangs
The diagram says 88 Mustang, but except for the vacuum line connected to the MAP/Baro sensor, it is the same for all 5.0 Mustangs from 87-93. The 89-93 Mustangs vent the MAP/Baro sensor to open air.
http://www.veryuseful.com/mustang/tech/engine/images/88Stang5.0Vacuum.gif

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

little5.0 · Aug 28, 2010

they are 21lb injectors out of a 99-04 mustang, they look sort of like the ones shown for the t-bird, they are pink tops. The stock injectors where shot. its just got me wondering, it back fires in the intake from what i can tell when i get on it, and is really sluggish. its the stock maf that cam with the car, i believe its a california model due to having a maf and being an 88. havent tune it or messed with the computer

Kdubslugga · Aug 28, 2010

Ive never heard of anyone using 21lbers before, dont know about that, but, if you changed injectors without changing mass air meter to a calibrated unit calibrated to your injectors, theres ur problem!!

Mustang5L5 · Aug 29, 2010

little5.0 said:
they are 21lb injectors out of a 99-04 mustang, they look sort of like the ones shown for the t-bird, they are pink tops. The stock injectors where shot. its just got me wondering, it back fires in the intake from what i can tell when i get on it, and is really sluggish. its the stock maf that cam with the car, i believe its a california model due to having a maf and being an 88. havent tune it or messed with the computer

Those may be 19s or 21s depending on who you talk to. Lots of arguements in 4.6 tech on what they are.

I think they are 21s, which means there is no calibrated maf for them. You need a custom tune, or you could try a 24# maf and see if the car can adjust its fuel strategy to the 21.5# injectors.

Also, what did you set then fuel pressure regulator to?

little5.0 · Aug 31, 2010

problem solved, it was a user error on my part, i miss read the haynes manual for the firing order and had it set for a non H.O. 5.0 instead of the H.O. 5.0, runs smoothly with no problems.

Idle/accel problems

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