There are many things I need to resolve on this car but one that has me currently frustrated is its deceleration behavior.

When I decelerate by releasing the throttle but using no brakes the engine bounces. By that I mean that it decelerates and then revs then decelerates then revs as I slow. It's not like I punched it when it revs, it's more subdued than that. Felt mostly as the deceleration stopping and the vehicle coasting followed by the forward tug of deceleration. Back and forth as I slow.

This happens wether or not I use the brakes as well, it's just more noticeable without them.

Lucas ingnition, if that's pertinent.

 

TPS is NOT set correctly for idle fuel map overrun.

 

Thanks Grant! I'll check it. It was sent to .34v but I did pull the pedestal for a new oil pressure sending unit. Maybe I disturbed it.

 

 

This isn't affected by engine temps that I can tell. But it only occurs on deceleration, and I let it warm before driving so...

She's idling at 900rpm in P 400-600rpm in D and then sometimes, for a lark, anywhere between 200-1300rpm. Depending upon her mood. Missing on a couple cylinders is playing havoc with the ECUs attempt at idle. New plug set (RS9YC) is in transit.

 

Try to get the idle stabilised at about 750 in neutral, so check the TPS, get the plugs and HT leads and dizzy cap and rotor changed if they are old. If the idle is fluctuating that could also be part of your problem as the overrun cutoff might be kicking in and out. The ECU automatically cuts the fuel if you are on a trailing throttle and the revs are over 1400 or so, then switches it back on as the revs drop. As Grant advised, the TPS setting will contribute to all this if it is off; my point is that you might have a few other things wrong as well. Eg: are the injectors of the missing cylinders firing irregularly, is the injector loom OK.
Greg

 

Greg,

Thanks, yes I likely have a few factors that are contributing to the issue. I haven't even begun to tune this car. Gapped the plugs to get it running, did the hoses and flushed rad. Found the tank leaky and fixed that. This weekend is tuneup time.

Just to confirm, would this 86 with the 16cu ECU have the ECU fuel cutoff feature or does it just have the overrun valves? I thought I read that cutoff was a 26cu addition. I could definately be wrong.

 

Yes, your car, like mine, definitely has the ECU fuel cutoff on the overrun. This is a fuel saving feature and also gives better engine braking.
The overrun valves are quite different, being a sprung loaded device on the forward end of each intake manifold, housed in a round thing bolted onto the manifold proper, which opens at a certain high manifold vacuum level to prevent too high a vac in the intakes and allegedly smooth out the situation on a closed throttle. This feature was deleted on later cars, and Grant's view is that they are completely unnecessary; he removed his.
Greg

 

That's my plan as well. I hope to clean up the engine bay quite a bit. If all goes well, relocating the Cruise bellows, Amplifier, injector harness, rerouting HT leads, and several other harnesses and hoses. It's very busy on top of that motor and I've seen some really nicely tidied-up examples that I liked a lot.

BTW what's the standard method of blanking the overrun valve end of the intakes? Does anyone sell an aluminum cap? I've seen plates fitted that I assume are shopped up at home. I suppose my friendly CNC guy could make me a nice aluminum cap that finishes the intake shape out nicely. He is friendly, but not cheep.

 

Remove the thing, make a template of the end and as you say, find someone to make a blanking plate. Great idea to tidy up the V.
Greg

 

I am also thinking that the AAV is having a serious female nmoment.

Here is a snap of my over run delete.

 

AAV is tested in a pot on the stove correct? Do I need to drain her first or can I just plug the AAVs coolant hole?

Oh I've seen your Overrun delete! And your other deletes! Your motor is largely the look I'm wanting. I may get a Sanden rather than delete the AC and I'd prefer to relocate the cruise bellows if I can find it a new home. But that opened up vee is the goal.

 

AAV is held to the head by 2 Torx setscrews, NO coolant hoses associated. The bulb out the bottom of the AAV sits in coolant inside the head. Some loss will occur, and easily topped offf when replaced.

The 90deg hose on top will split, so order a new one FIRST.

The cruise bellows will fit in the opening in front of the RHF wheel. Wedged in there with the spare vac tank. Lots of alcohol to get the angle of the dangle just right. A half decent sense of adventure is also a good thing. A cable extension will be needed. I got one from Harley Heaven here, worked a treat until I upgraded the cruise.

 

SOLVED.

This weekend I capped the overrun valves intakes and this symptom was completely alleviated. Apparently my valves are flakey. I don't care; they're going to go away soon.

 

Well done, great news.
Greg

 

Well done.

What are we now drinking???????????

 

Woodford Reserve. Kentucky straight bourbon whisky. Seriously smooth deceleration.

 

Old post from the dead.

Did u delete your fuel cooler as well since it is connected to the overrun?

Also the fuel lines go into the 2 circled items in the picture. How did u do the work around?