joel5.0
New Member
Nothing, and it has nothing to do with the readings at the MAP sensor.
The Speed Density fuel injection system is based on an assumption of the volumetric efficiency of the engine. When you modify the engine from stock, you're changing it's volumetic efficiency, however the computer cannot compensate for this because it has no way to know.
So as you do mods like a free flowing exhaust, that ultimately allow the engine to breath more air, you're not getting any more fuel with it, and you go lean. Even with all the electronics working.
Fordguy,
Your sig says that your 87 is mostly stock. If that's true, you shouldn't have any mod-induced lean condition. The fuel pressure numbers you're getting are what they should be.
Take it from someone who worked in a shop, you don't want to take your car to one. Shops throw money and parts at cars, they catch hell trying to charge customers diagnostic labor hours to actually troubleshoot a problem so they don't even try. A bad temp sensor could be the cause, but I seriously doubt that was more than an educated guess. If you want to know what's really wrong and not pay out the nose for it, you're going to need to do the troubleshooting yourself.
Pull codes like JR suggested. Off the top of my head, test your coolant temp sensor (new doesn't mean good), your intake air temp sensor, your MAP sensor, and your EGR position sensor... a remote possibility is there's something up with the EGR position sensor, telling the computer the EGR valve is open when it's not. When the computer thinks the EGR valve is open it pulls out fuel.
If the system goes lean, lean code failures should be output by the system informing any fuel trim correction required falls above the EEC fuel trim capabilities. If this would not be true, installing 24# injectors in a SD system wouldn't be a problem, yet, it is....... with the 42 and 92 system rich codes showing in a self test...... have I done it?..... yep, found out about it back in 1992.
The generalization that SD systems do not monitor A/F and not try to correct any deviations from the optimum stoichiometry is wrong, otherwise, they would not have passed EPA regulations. SD systems "fault" is that they attempt to correct A/F "after the fact", based on engine vacuum output as a signal of their efficiency however, the O2 inputs are also used (provided closed loop is achieved)..... IOW, the EEC does have a way to know. Have I worked street SD setups with 80mm TB's, better flowing intakes, exhaust systems, cat-less non-emissions, better flowing headers (ST's and LT's)?......... yep.