Warm Cruise Driveablilty Problem

[MikeO]

I'm having a moderate to severe driveabilty problem with the engine bucking and hesitating at part throttle cruise. It only occurs when the engine is warm and improves when I disconnect the O2 sensors. I got the car on the road in April (just before the "Deadline") and have had the problem from day-one. I've gone through everything to check for and repair any vacuum leaks.

I'm running a new Ford Racing Boss 302 crate motor and Mass-Flo EFI system with 30lb injectors. I'm not getting any trouble codes.

Has anyone had a similar problem or any thoughts on how to diagnose this?

[turbodon]

This would indicate you are lean at this throttle in Closed loop table.

When you remove the O2 sensors and force to open loop (or cold motor) the open loop mode VE table is richer.

What is your fuel pressure? The 30lb injectors? 2 bar or 3 bar?

[JKleiner]

You don't have the O2 sensor wires swapped side to side do you (i.e. right side wire reading left bank sensor and vice-versa)?

Jeff

[Michael Everson]

Try blocking off the front of the air cleaner and tell me if the problem goes away.
Mike

[Radar Pete]

Same prob. VSS kinda to blame. Tried many fixes, but just live with it.

[con9k@aol.com]

If your air cleaner is mounted in the fender well above the headers your intake air is too hot on humid days. You can add a 3 1/2" dia. X 18" flex duct between the air cleaner and the Mass-Flo then relocate the air cleaner up front behind the radiator into cooler air. I then wrapped the intake tube with a heat shield blanket. Intake air went from 170 degrees to less than 100 degrees. Problem solved. If you need pictures email or PM me.

[MikeO]

Thanks for all the replies. Sorry it took so long for me to respond...family stuff took a priority

I'll try to answer all the questions in one shot:

1. I'm running 40 psi fuel pressure
2. The connectors for the O2 sensors were labeled and the way the harness is designed would make it almost impossible to switch right and left sensor leads.
3. I called Mass-Flo about this problem sometime in May and the Tech Support guy I spoke with said the problem may be due to the ram air effect of the hood scoop causing turbulent flow through the MAF. He suggested I block off the front of the air cleaner to help smooth it out. I did reduce the problem, but didn't completely eliminate it.

turbodon - I hear what your saying...in fact the reason I disconnected the O2 sensors was to force it into open loop to see if the richer fuel settings would cure the problem - made it better, but didn't cure it.

[Bob Cowan]

The first thing to check is the fuel mixture. Just like any job, you need to invest a little cash in the right tools. Spend the money and buy an LM-1. Otherwise you're just guessing what your mixture might be.

Second, what's your ignition system like? Too much timing coupled with not enough fuel can do exactly what you're describing. Adding more fuel can improve it, by making it run rich.

[dale]

Same issue; keep us updated, please.