new motor-getting knock/detonation...

wmu-sc

Registered User
I just installed a freshly built new motor, all new parts inside, balanced and happy.

Runs smooth, but when the engine is revved or loaded, it develops a slight knock to it. I actually had a guy stop me on the road and ask me if my car was detonating. When the engine is at a constant RPM, it runs very smooth and quiet. I can't detect the knocking sound (doesn't mean it's necessarily not there)

This sound had existed just before I lost my crank...I had attributed it before to losing a main bearing. Now I'm not sure -

Could I be losing the knock sensor? Could it be Cam sensor? Could it be Cam Sensor positioning? Crank Sensor? All these things are unchanged since the before the rebuild. Is there a good way to go about diagnosing this?

Thanks in advance for any advice...
-Steve
collegiatepenury@yahoo.com
 
Just bored .020 over, and had new pistons & rods matched & balanced. Sealed Power Rings, Bearings.

Bought a used Crank, had it polished, opened up the oil passages (Ever-so-slightly) and rechamfered.

Stock stamped rockers & pushrods.

Heads are freshly milled, new valves, guides, seats, etc.
Stock sizes. No porting or anything.

Nothing radical, just wanted to bring everything up to par.

Stock Manifolds (Ground open), catless xhaust, stock resonator & mufflers.

Custom Cold-air intake, 9" K&N Cone.

Does that help?
 
Well, first thing I would do is get rid of that resonator. It is the biggest restriction in our system. When I added a cat to the center of my system i started detonating right away so I am sure the res is causing a bunch of problems. You probably added a little compression when you had your heads milled so that would increase chance of detonating. Also fuel may be a problem so make sure to use a good station and only premium. As far as sensors go, the only one that would create that prob would be knock sensor and I haven't heard of many of those going, but if it is cheap then may want to try. And one last thing, the conical filter, if it is in engine compartment and not shielded, you are feeding your car hot air which would cause detonation too. Try to shield it so all it gets is cold air from the wheel well.
 
I have a new 2-1/2" exhaust, with a flowmaster resonator, but it was too long, and I need to fab some new pipes to fit out the back.

I'm just a little unsure as to whether or not it's detonation. It's sorta like the sound of it, but it seems to me to be a little more of a hard knock....I could be wrong, though.

What strikes me as odd is that this knocking/whatever existed before I yanked the engine, and rebuilt it. So it's either in the top end....or another system..? I just got back from lunch, and it's pretty pronounced. It makes me cringe to drive the poor thing, but I'm not sure where exactly to start....
 
Last edited:
that res can cause a lot of problems. Our exhaust was already bad, but add on stuff and it makes it much worse. I'd say fix exhaust and shield air filter and your prob will go away.
 
I'll give it a shot....
To be honest, when I started the car with the Flowmaster (and no mufflers) I didn't hear the sound.

As for the K&N, it's in the wheel well. No warm air getting to it.

But I think you're definitely onto it. I'll let you know what happens.

-S
 
Aaron basically covered it, but you might also want to try a bottle of fuel injector cleaner and to make sure you have sufficient fuel pressure at the rail. Try the search function for "checking fuel pressure" and see what you get. I am sure there have been threads about this before.

Alex
 
Dude, I've been dealin' with that nasty detonation for quite a while now. Hopefully you have an EGR delete so you won't have to worry about that. If you do, get a vacuum on it. Pull vacuum til it stalls or near stall. If not, replace it. Also check your metal EGR tube for cracks as well as your vac tube from the transducer to the exhaust. Check for vacuum leaks. Double check your timing with a light. If possible try to isolate the bank or possibly the cyl by having someone load the motor with the brake on. Not the best way though. A dyno would be ideal with a scope and scanner. Also check your MAF output. You mentioned your running a 9in conical and MAF sensors can misread incoming air depending on how its mounted(read that somewhere). Good luck. Sound off when you solved it.
 
Last edited:
New plugs in....no difference. Sound still there.

SO - I replaced with the Autolite DBL-Platinums (764s I think is the number...I dont have them right here). NO difference. The sound is there, throughout the entire range, it's louder as you give it throttle....either loading or just revving in neutral.

Next question - is there an easy way to make sure the Cam Sensor is in the correct orientation? That would of course lead to timing issues, but I'm not convinced this is the problem as the knock sensor "SHOULD" retard the timing.

Any other suggestions?

-Steve
 
Check your PCV valve and make sure it's not froze open. I had one go bad in my car and it pinged like crazy. Besides, it's cheap and best to start with the small inexpensive things that can go bad first.

Good luck
 
knock

I had a loud knock at one time on my car. Sounded like a piston knocking. It was the plastic cover that goes around the harmonic balancer. It had worked itself loose and was knocking on the balancer. It's worth a shot to check.

mark
 
engine noise

you did all this work to that engine i hope you changed the lifters.if i were you i would eliminate base engine concerns, and get rid of those autolite plugs MOTORCRAFT only.I did read some good advise especially look for an exhaust leak....good luck....Doug
 
Leaking Injector????

Replaced the PCV....also changed over the exhaust to 2-1/2" into a 3" Flowmaster.

Knock still there.

Loosened the Cam Position Sensor, and rotated it back and forth 15 degrees or so, and nothing happened, which is really what I expected to see. The computer compensated for the timing.

I didn't change the lifters, but I gaged everything and everything is dead nuts. I wanted to go roller rockers, but money didn't allow at the time of rebuild.

So here's my thoughts - Could I have a leaky injector? The little orange "hats" on the ends of some of the injectors were cracked, but I really had no clue what function they served. Nonetheless, in theory, if I have an injector leaking, then it would cause pre-detonation that would make the sound I am hearing. I ran a KOER test, and the EEC returned the right bank is running rich. This also would lead me to believe that an injector is dumping gas into the piston.

However, would the leak be enough to pick up on a Schrader pressure gauge? Also, is there any way to know which injector is bad, or should I just replace the whole array? If so, where should I go to get a set of replacement injectors?

Thanks for all of your input, I appreciate everyone's help thus far.

-Steve
 
Back
Top