I have a 1986 f250 460 it has a holley sniper tbi with the holley hyperpark ignition and distributor it has flowtech headers no smog pumps or egr weiend stealth intake manifold and top dead center timing gears it was running great but I decided to swap the cam out for a little more power I ordered a comp cams xtreme 4x4 camshaft with lifters and valve springs after replacing the camshaft and ordering pushrods I started the motor today it is crazy loud out the exhaust and not in a good way it sounds like it went from a full exhaust to a straight pipe the idle is not good very choppy feels like it is misfiring and the engine is shaking whole truck I checked timing multiple times and have the base timing at 16 degrees wich is what it was before the swap I tried adjusting it from 10 to 20 degrees and no change getting to 5 it starts having a hard time running and 25 it starts getting worse and louder the afr is 13.5 to 1 at idle wich is where it ran before I have not tried giving it more/less fuel at this point as I didnt feel it was the problem I have no vacuum no accessories and no power brakes I have checked multiple times for leaks and everything appears to be sealed up I tried driving it and it sounded like a straight piped idi diesel it has no power past 1300 rpms and it runs terrible chugging and really loud but the sound seems to be all from the exhaust not from engine bay when I put the cam/crank gears on I turned the crankshaft till I felt pressure pushing my thumb from the spark plug hole then put the crank gear on and turned the crank a little more till the dot was directly up I then put the chain on and installed the cam gear with the dot facing down towards towards the crank gear dot I then installed timing cover etc. I put the engine back to tdc cylinder 1 and installed the distributor I had made two timing mark's one on the distributor and one on the engine when it was tdc before removing so I put it back in the same spot i removed it. Could I have the crank gear 180° out? Would that actually effect anything? Could my pushrods be to short or long? I didnt feel very confident when measuring them. Also I have stock rockers non adjustable the pushrods I installed are 8.450

 

Try beaking in the cam with a carb could be to much of a change. Did comp say this cam will work with EFI? might need to narrow down the issue. I would toss out not as many Have experience with Holley sniper EFI and likley even less in a cam swap situation just .02$

 

If your AFR is 13.5 at idle then you don't have a fuel problem at idle. What is it when you drive down the road at part throttle?

Some cams are aimed so much to make power at high rpm that idle really sucks because of the lack of vacuum. But a 4x4 cam shouldn't be like that.

 

Did you check lifter preload ?

 

Thank you for the reply I have not checked the afr at part throttle only because it was idling so terrible but I will check. I am thinking it may be lifter preload. I measured and ordered pushrods but I think I messed it up. I ended up to busy this weekend to look at it so I'm hoping soon I will be at it again. As far as the holley sniper i know it adds a lot of variables but people are running this setup on way more custom builds than mine with larger cams and it comes with settings specific to large cams with holley saying it will work (for what that's worth). So for now I'm putting it on the back burner for ideas.

Also I have no vaccum with zero leaks in the system and comp cams said this cam should have adequate vacuum for accessories. So I'm fairly sure it's a mechanical problem at this point.

 

If its getting 13.7 AFR at idle I wouldn’t think it’s the pushrods. If they’re too long the valves are hanging open and it be running very rich. Does it smell rich? If they’re too short it would be making quite a racket.

 

Yes the afr was reading 13.7. I have been thinking tho and with it being a closed loop system it can correct the afr very well from my experience. And I have it set to something high like almost 200% correction allowed. So it seems like it may be possible that even if one cylinder wasn't firing or they were all rich it would just keep cutting/adding fuel till it dropped to the set idle afr parameter. I wonder if I should drop the allowed correction and see where it really is? But I think I am still going to recheck the lifter preload anyway just to be certain plus I want to rule it out. Thank you for the reply!!

 

Yeah that certainly could be. When I rebuilt my 351w a few years back the pushrods were not properly measured. I kept the stock cam but had a refurbished set of GT40P's. Upon the first start-up, it was running very rich. I had to set the base timing to something like 30 degrees ATDC just to get it to idle. It was way down on power. The pushrods ended up being about 0.050" too long. It caused the valves to hang open. Once I got the proper size pushrods, all was well. The cam had a real lopey sound to it, thanks to the pushrods being too long hanging the valves. Again, this was the stock F4TE camshaft. Does the Holley Sniper run closed loop even at a cold start, or does it run closed loop after the engine reaches a certain temp? I don't know anything about that system but the PiMP ECU I have enters closed loop after 160 degrees coolant temp. Is there a bad misfire can you tell?

 

If one cylinder isn't firing the fuel system will not be able to cover that. The oxygen sensor will be so far off that you wouldn't see 13.7. I suggest getting a degree wheel, pulling a valve cover and verifying your cam timing.

 

Solved!

So my valve spring retainers were to tall. I didnt know that was a thing, but they were allowing the spring to relax too much to a point where it took minimal force to open the valve about a 16th of an inch. This made the lifters overpower the valve spring and hold the valve open. When I first started the truck it would fire up build oil pressure then die and have no compression. I could turn it by hand a few times and it would get compression again then repeat cycle. I then got pushrods that were .05 shorter thinking my pushrods were too long as it appeared that way. This is where my post was made. The noises I was hearing were valve lash but with he truck back in on the side of the house all I could hear was exhaust. After replacing the valve retainers with factory ones same seats and springs and going back to the longer pushrods I have full vacuum and the truck is running again.