Installed the ubiquitous billet adjustable fuel pressure regulator on my 85.5 autoXer recently. All went well and theory of the mod seems sound...as we didn't make the move until I did a cat removal custom 2.25 exhaust (to keep torque) with a Delta 40 Flowmaster and wrapped the header. Seemed to me that the motor was sounding "lean" above 4,500 rpm so we decided to up the fuel flow at little.

Ran great and really surged as rpm's climbed. All good.

But about two weeks ago, the motor developed a skipping burbling miss on decel. It was spooky as it seemed to be a function of trottle angle and sometimes effected idle after hard passes. After messing a little bit with the theory that fuel pressure was too high for the OE injectors, we found a bad vacuum connection at the "T" on the passenger side firewall. Reinserted vacuum line and problem went away.

Now I'm starting to get it again, intermittantly, and the motor will begin to miss badly when I get back on throttle after a skipping decel event. Goes away as soon as I feather the throttle and get back on it.

Any similar experiences? Maybe still vacuum? Failing injector? Martians? Small toad or dwarf in my stomach?

 

Have you checked your spark plugs or your ignition system? If the engine is missing I could only assume it would be because there is not sufficient spark to ignite the fuel.

 

Checked spark plugs, wires and distributor...all new within the last 24 months, but checked anyway. Pulled plugs looking for signs of misfire, no fire or oiling. Found nothing, swapped out from platinum Bosch to copper Bosch just in case with no impact one way or the other is the skip.

I'm assuming (perhaps not a good thing) that I'm losing a cylinder due to fuel availability since stuff started happening after I upped the fuel pressure from 36 to 41 psi and because the first time the situation occured it went away when we reconnected an open vacuum connector, which effects the FPR's response to open and closed throttle.

Can anyone post a laymen's version of what happens when an injector stops pulsing in the face of excessive fuel pressure? And could this be my issue?

 

What type of p-car do you have?? I dont think you are maxing out the injecotrs, Im running 45psi at idle and I have no problems in my 87 924S, the injector will not stop injecting if there is too much fuel, What happens when a injector has maxed out its flow is it will just reach a plato and not be able to get any more fuel in. I dont think the miss is because your injectors cant get fuel in, Sounds to me like a vacuum leak or bad ignition component. You might also want to run some injector cleaner threw the fuel system. What else have you done to you ride??? If you havent increased the air flow into the motor there should be no reason to install a FPR. Also you might want to get your hands on a A/F gauge so you can see whats going on.

 

I have an NA. Good ideas, all. I've improved the scavanging with new custom exhaust from the down pipe back, cat delete and flowmaster 40 and we wrapped the header. Only change on the intake side is a K&N in the stock box...which I'm not all that enamoured with anyway and often run a fresh paper filter instead. Have run a couple loads of injector cleaner as suggested, but haven't really taken the time to install a fuel rail gauge. As you say, its time to get serious about the vacuum and A/F. Do the various rubber vacuum fittings loose their seal to the vacuum lines over time? None of them look shaky at a glance, but I'm tempted to get one of those fancy blue line kits and replumb all the vacuum stuff while I'm at it.