engine rattle on acceleration-help
 

hey everyone
i'm having a problem with my daughter's fuel injected throttle body 302. while its not in a cobra i need some help. the engine is in an 88 full size ford bronco. the engine has been rebuilt and has all new parts including computer, injectors, sensors, distributor, coil, etc. she has had different mechanics work on it and still there is a problem. under any kind of acceleration the engine makes a terrible clattering noise. i've reduced the timing to '0' and it will run ok around town for short jaunts. once on the road after 30 or so miles then it starts with the chatter under load. even going to 93 octane doesn't seem to help that much. if the timing is set at around 10 degrees the engine will not accelerate without clattering. what is going on. the engine worked fine before the rebuild. but since it had over 225,000 miles i thought it best to rebuild. now i am frustrated with the results. help!!
thanks,
paul

Hey Paul,
I'm no EFI expert so I'll stick to the basics. Given the things you've tried, it appears you're convinced it's pre-ignition/detonation knock.
When this engine was rebuilt were stock parts used? No high compression pistons, etc?
Were the heads milled and/or the block decked? Was the cam changed? Do you have the equipment on hand to check whether the cam is in time?

It seems like the 'controller' is not listening to the parameters of the motor and not making the necessary adjustments. Do you still have the original parts? I would swap the sensors and computer in one at a time to see what changes if anything.

Which 302 firing order are you using?

Sounds like pre-ignition (detonation) from too much timing. But, is it really? Put a timing light on it, and run the rpm's up to 2,500'ish. If your timing goes above 34* or so, then that is the problem. If not, don't waste time (and money) changing distributers and ignition parts.

The engine probably does not have headers. But run it down the highway in 3rd gear (high rpm's for a few minutes. Pull over quickly, jump out, and put a infrared thermometer on the exhaust manifold - as close to the head port as possible. If one is hotter than the others, it's running lean, and that's the cause of the detonation.

Are we sure it's detonation? Could it be a noisy lifter under a load? Stock heads probably use a pedastal rocker. Maybe the engine builder just bolted it together and didn't check valve settings properly.

Hey, Paul, does the setup have a knock sensor? Did you change it? Is it connected? I think a bad (inoperative) knock sensor will cause the computer to keep adding timing looking for incipient (or insidious?) knock. Just trying to think of simple stuff that might be worth checking. Good luck, and let us know what you find.

During this work that was performed on the engine, were the heads taken off and gone through? On a high mileage engine, deposits can exist in the combustion chamber that can cause inaccurate information to be furnished to the efi.

hey guys
thanks for the quick replys. a breif history. the engine ran fine, even with 225,000 miles. the tranny went out so i decided to rebuild the engine while the tranny was being rebuilt. my engine builder has been my builder for years and has built all the engines both for my cars and for my customers. i've never had a problem with an engine he built no matter how radical the build. this engine showed almost no wear. my daughter knows how to take care of her cars by maintaining regular maintenance. the engine was built back to stock specs including cam. as for as i know the new computer is correct for the vehicle. i'm sure the noise is not the lifters or rockers. they are of the pedestal type. with the timing set at stock specs of 10 degrees, when you try to accelerate the noise from the engine sounds like someone shaking a tub full of cans. i had to back the timing down to 0 to get rid of the nose. at 10 degrees after tds there is no noise even under load. but it runs like a dog and gets horrible gas mileage. i am a little suspicious of the knock sensor. the boss in the block cracked so it was drilled and tapped with a brass fitting and then the knock sensor was screwed into the fitting. it has the shorty tube headers. i will be seeing her this weekend for fathers day and would like to check out possible solutions while i'm there. can the knock sensor be by passed to see if that helps with the problem? i'll check the total timing as well. dad is getting tired of working on this car.
thanks for the help and happy fathers day,
paul

Paul,

I'd nearly bet the incorrect fitting of the knock sensor is your cause.

They need to be fitted in the block by the correct depth to the specified torque.

Is the valve timing correct?

try pulling the spout connector to limit timing. set base timing to 10 degrees an take a run. it shouldn't advance timing therefore shouldn't knock.
the knock sensor detects the timing advance and the computer maintains maximum advance for maximum economy.

Paul, hook up a timing lite, and with the motor idling, rap fairly sharply on the block near the knock sensor...if it is working the computer should retard the timing.

thanks guys. i'll try the tests this weekend when i see my daughter and report back on the results. ken-when are you coming back to texas? hope you are doing ok. give me a call when you get a chance. usually get home by 9 PM and i stay up late. 361 549-9525.

Have you checked the cam to crank timing? If the clattering is that bad is seems more generic not related to FI.

Paul,
Have you turned the engine to top dead center and checked the balancer for being on the 0 mark? I just changed one because it came loose and turned giving the wrong timing mark.

Just to get everything possible on the table:

Intake leak causing motor to go lean under acceleration might be a possibility.

Might check for higher than expected oil consumption (not sure your motor is susceptible to this so others might have good info). If the motor can suck oil, it will cause hot spots as well and really make a noise under almost any kind of acceleration. You should see a bit of smoke on early acceleration on the side leaking (again, if that motor is susceptible to internal intake leaks).

Does sound like the knock sensor though doesn't it.

Good luck.

hey guys
sorry for just now reporting in. got back late from austin and then it has been a busy week. anyway, the timing was off. it dawned on me to check my timing light dial and sure enough it was set at 16 degees instead of zero. i loaned it out to a friend and didn't think to check the dial. reset the timing and things are better. still not sure about the knock sensor. my daughter is coming into town next weekend so i'll try to do more checking. thanks for all of the help, and i agree that it still could be the knock sensor.
thanks,
paul