Thread: Driveability issues

Tweet

Need some advice. My 351 Windsor just will not run smooth or drive smooth. It has a Gearstar AOD which won't shift out of 4th gear until almost stopped causing severe bucking and it shifts too soon (needs more pressure I think). The real problem is the FAST EFI on the Edelbrock Performer RPM air gap manifold. It just won't run smooth and stumbles just like a carb would. It runs rich no matter what I do. FAST says the O2 sensor is too close to the 4 pipes as the come into the collector (I'm about 1 1/2 inches away just like many other headers I've seen with O2 bungs). My muffler and extension hook on about 3 inches from the O2 sensor and I've done everything I can to stop the leaking at the slip joint. If I can keep the engine above 2000rpm the car runs decently. Opinions? Too much manifold for the application? The car is a cruiser. The engine only made about 365hp on the dyno with a 650 carb. The dyno shop couldn't hook up the efi for tuning purposes.

I don't think the manifold is an issue. Certainly the manifold is not causing the rich run condition.
If the oem says the sensor is to close, then you'll need to follow their suggestion(s).
But you can also do things like verify the timing and the vacuum in the intake. Also verify the plug wires and they're location, fuel pressure?? any of those basics will influence the motor.

Did the oem say how far back to install the bung for the O2 sensor?

Have you checked for a vacuum leak? What do you have for an ignition system?

a Friend had a supercharged 454 (1990) that the cam was off 3 teeth it would show in time with the efi but it ran eye watering rich, had to tear back into it, correct cam, efi acted perfect after that.
I think the efi was hunting for the right signal/nixture. I cant believe it ran as good as it did.

Keep us posted what you find out.

Godspeed
MrC.

leaky slip tubes=faulty AFR at the sensor showing lean so the efi tries to richen the mixture----------

You need to get a better collector to muffler connector that seals tight. Your FAST system is self learning on the tune, right? And you're running a wide band O2 sensor, right?

Thanks for all your input. I have checked for vacuum leaks, the car is properly wired, new O2 sensor, etc. That is what is driving me crazy. The only way I can correct the O2 location is to make up some new headers with shorter runners, longer collector, to get the O2 sensor farther away from the 4 pipes, closer to the engine, and farther away from the slip joint of the muffler. I think I'll just hang a carb on it and be done.

an O2 sensor will work anywhere in the exhaust, from the first 2 inches to the end of the tailpipe---------------I have seen dozens (maybe hundreds) of deals such as your talking about-------and almost everytime the problems are caused by some poor assed install work where there are sloppy fab or install work-----------you talk about slip joint header tubes collector length---------------your probably got some leakage along the tubes/joints and are sucking in air at slower speeds which then is sampled by the O2 as a lean mixture and the ecm self learn richens up the mixture to compensate----------of course tho, it could be a leak anywhere in the system where as the sensors aren't measuring it----------mass air flow, throttle body, idle air, map---or defect on a temp sensor---water, inlet air, etc----------

I don't see any problem with the O2 sensor being in a primary, and if the slip joint is downstream of the sensor it's not likely the source of your problem. If the O2 were two or three inches from the open end of the pipe you might be getting backwash, but not likely with a slip joint leak. The only issue with having your sensor in a primary is that you're only sensing one cylinder but that's generally not an issue unless you happen to get a firing problem in that one, like a bad plug or wire. Looking back at post #6, is your FAST a self learn/self tune system and is your O2 sensor wide band or narrow? Also from post #3, what ignition are you running. Keep the dialog going and we'll try to get some focus to your solution process. Hanging a carb on should be a last resort, IMO.

well, actually, having an leaky slip joint downstream of an O2 sensor that is close to the junction of the primary header tubes can and often does, create an much more vulnerable source for the backfeed caused by the backflow of the exhaust on overlap to a particular cyl.


I am not saying that is the cause in this case because without seeing the particulars first hand-----------

Proeagles, as I read your initial post you have four primaries that are tightly welded into the collector, and your O2 sensor is in one of the primaries just before it flows into the collector. Then you have a slip joint reducer that's over the collector, flowing into the exhaust pipe/muffler, is that right?

Jerry, can we let Proeagle answer this question, plus the questions in #9 before we jump into the "what if's" again? We need a better understanding of the system to engage in any discussion of substance, IMO.

You maybe looking at this from the wrong end if there is an eng. misfire unburned fuel charge and unburned o2 are sent down stream the o2 sensor sees this o2 as a lean condition and tries to correct the a/f mixture the thing I would do is check compression to eliminate a mechanical misfire like valve too tight flat cam broken piston ring then be sure there is not an ign. misfire like spark plug, plug wire, dist. cap rotor or coil diagnose the problem so you not running around chasing your tail ok that's my 2¢ worth ......ted

The O2 sensor is not in the primary tube, it is in the collector 1 1/2 inch from where the 4 pipes come together. FAST is the one saying the O2 sensor is too close to the 4 tubes but unless I completely remake the headers which are from Sanderson, the O2 sensor is where it has to be. The slip joint is leaking and it is less than 2 inches from the O2 sensor. I'm thinking of getting some header wrap and putting it around the joint to test the theory of the leak downstream of the O2 sensor. I remapped the computer today and it is better but the system just doesn't seem to be learning like it should. A quick check at the exhaust showed a 16:1 AFM and so I changed it back to about 14:1. I'm using a MSD distributor and MSD box to brighten the fire, I'm on my second box. The plugs have been changed, regapped and I corrected the timing to about 10 degrees at idle. The timing was way off, have no idea how the builder could have done that, that bad. I'm almost there engine wise after today's tuning. My biggest problem now is the damn transmission won't down shift soon enough lugging the engine, not to mention that it upshifts at 5KRPM at WOT. It also won't stay in a gear I've selected for it. For example if I place the lever in low, it will shift up three gears. At least I can keep it out of 4th which presents the biggest problems. As long as the engine is purring along at or above 2K RPM, it runs nice. Anything below that and it surges, even at 40 mph in 4th. With the car sitting still, in neutral or park, blipping the throttle to 4 or 5K rpm the engine sounds awesome, no miss firing.

What transmission?

Proeagles, I don't know the specifics of the FAST system, but your base timing is an important number, as the ECU spark maps will add to the base value that's in their programming. My Edelbrock unit requires the timing to be set at 10 BTDC. Having it a few degrees later will just affect performance, but bumping your base timing more advanced could be more catastrophic if you're pushing the limits on total timing in the computer. It might not be convenient, but can you weld on a three bolt collector end plate, and a corresponding one on your exhaust for a gasketed, leak free joint at the collector? I don't like the idea of a slip joint there, given the proximity to the O2 sensor. Or better yet, fix the leak and move your O2 sensor down into the exhaust pipe as opposed to the collector?