Valves clack when warm

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Jun 3, 2004 | 09:31 AM

GWTarpon

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Valves clack when warm

OK crew, here is my latest problem...

I pulled my rear cat and replaced it with straight pipe. Noticeably more power when the engine is cold and warming up. When the engine gets hot, I hear the valves clacking at highways speeds ;if I try to punch it, and I have noticeable less power. By "hot" I mean that the temp gauge is at about 3/8 to 1/2 tank of heat. Not really hot. Only happens on warmer days. I have a new thermostat and recently flushed the cooling system, also have a new coolant temp sensor. I suspect that replacing the cat with pipe is causing it to run a bit too lean when warmed up, and that is causing cylinder head temp to be a bit too high . Also could be an ignition timing issue. Any ideas, any fixes ???

Jun 3, 2004 | 08:06 PM

ronbo862

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The valve "clacking" may be pre-detonation, did you check your timing? You may have to back it off a bit. The heat and loss of power is also another indication. Good luck!

Jun 4, 2004 | 08:44 AM

GWTarpon

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That [timing] is one of my theories. I would think the computer would adjust it, but maybe not. I do not have a timing light, so I pulled the SPOUT connecter and times by ear. Replaced the spout and went on my merry way. It just doesn;t sound like the ping of pre-detonation., though...

Jun 5, 2004 | 02:44 PM

javi2001

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Unfortunatelly, the age of "times by ear" is very away, Computer makes changes on timing asuming the Base timing is right ( 10°) so you should get a timing lamp and set it...

Jun 5, 2004 | 08:46 PM

ronbo862

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I've never totally gotten rid of valve clatter in this engine. You could try and advance it a bit so you definitely know the difference between valve clatter and ping, then back it off. You definitely have to set it to base to make it work right though. The curve in the distributor is also designed to work with the base timing AND the computer.

Jun 6, 2004 | 03:18 PM

javi2001

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From: Venezuela

Note: TFI-IV module is a dummy ignition system, it means; ignition module and/or distributor doesn't have ANY controll over ignition time, module just provide a base timing for computer, wich makes calculations base on air temp, TPS, engine vacum, RPM, engine temp and knoking sensor to provide a signal to module to advance timig know as SPOUT (Spark Out)

In case there is no SPOUT signal present, TFI-IV module reverte to a test mode and use base timing as ignition timing so mechanic can adjust base timing without computer interference.

Jun 7, 2004 | 03:14 PM

GWTarpon

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Actually,Javi, Ronbo, etc, you are almost right. The computer does adjust ignition timing within a certain range, I think it is up to 20 degrees plus or minus from the mechanical setting. The nominal mech setting is 10 deg btdc. That is why you have to remove the spout to keep the computer from modifying the timing while you are rotating the distributor. Once you are set to 10 deg btdc mechanically and the spout is in place, the computer uses the PIP signal to electronically adjust timing to the optimum setting for driving conditions and the fuel.
I was thinking that I had it set so far off that the compter couldn't compensate, but I suspect is is just something making me run lean when the engine is hot.