I recently had the ecm replaced in my caprice after the car mysteriously started backfiring one day while putting load on the engine. The shop also replaced a couple other sensors and the EST module.
The car runs so much better now, but the engine now makes a rattling noise going up hills on the highway. But this only starts occuring when the engine reaches operating temperature because on the drive to work there are 2 hills on the highway I take, it doesn't rattle on the first one but it always on the second one much farther down the road. I replaced the EGR valve and the vaccuum solenoid and they are working now as per the dianostic tests in the shop manual. I tried to check the timing but alas my timing mark is no longer readable so I really have no idea if the ignition timing is correct. I'm pretty sure the rattle is due to pre-ignition because it is reduced when using premium but it doesn't completely go away. I also tried Seafome and that didn't do anything either. Does anyone have any suggestions as to what I should check next or what might be the cause because I really can't afford to take this car back to the shop and have them charge me and arm and a leg and keep my car for 4 days trying to figure out the problem.

I recently had the ecm replaced in my caprice after the car mysteriously started backfiring one day while putting load on the engine. The shop also replaced a couple other sensors and the EST module.
The car runs so much better now, but the engine now makes a rattling noise going up hills on the highway. But this only starts occuring when the engine reaches operating temperature because on the drive to work there are 2 hills on the highway I take, it doesn't rattle on the first one but it always on the second one much farther down the road. I replaced the EGR valve and the vaccuum solenoid and they are working now as per the dianostic tests in the shop manual. I tried to check the timing but alas my timing mark is no longer readable so I really have no idea if the ignition timing is correct. I'm pretty sure the rattle is due to pre-ignition because it is reduced when using premium but it doesn't completely go away. I also tried Seafome and that didn't do anything either. Does anyone have any suggestions as to what I should check next or what might be the cause because I really can't afford to take this car back to the shop and have them charge me and arm and a leg and keep my car for 4 days trying to figure out the problem.

EST module? EST is handled directly by the ECM, an "ESC module" (electronic spark control) is external to the ECM but uses a detonation (knock) sensor. If your car has a knock sensor, it has ESC - no knock sensor, no ESC.

Well, the rattling you are experiencing definitely sounds like detonation! If your car has ESC, your new module may be improperly hooked up, malfunctioning, incorrect for the car, or the knock sensor itself may be tango uniform. FWIW, knock sensors are extremely fragile!

Use a higher test gasoline, or retard the timing a couple of degrees (your power will drop) until you get the ESC taken care of. Serious or prolonged detonation can result in damage, including but not limited to:

*Broken spark plugs
*Bent valves
*Broken pistons
*Melted pistons
*Blown head gaskets

Thanks for the quick reply and for correcting me, was reading about how the EST works in the book so I guess thats why I called it that. The ESC module is the one in the distributor correct? The shop I took it to replaced that and the map sensor. The knock sensor should be on the intake manifold somewhere should it not? I will retard the timing a couple of degrees and see what happens.

You're on the right track trying to check the timing, but if it turns out to be correct, you should take a llok at your EGR system. If the vacuum lines get cracked, or the solenoid is unplugged or stops woking, the valve won't open, and you'll get high combustion chamber temperatures that will cause detonaton. Also, the exhaust passages on the intake manifold can clog and cause the same problem.

I'm 98% sure the egr system is working properly. I replaced the valve and the solenoid and I spent 20 minutes cleaning a ton of crap out of the egr passages. When I lift up on the valve the RPMs drop and when I rev the engine in park the valve doesn't move. Also with the 4 pin connector distonected from the distributor and the test terminal grounded the valve moves exactly how its supposed to according to the shop manual. Would it be possible that I maybe didn't get all the crap out of the egr passages? There was a ton of stuff that came out of it when I cleaned it. Is there any way to clean it out other than scooping it out with a screw driver that works better?

Thanks for the quick reply and for correcting me, was reading about how the EST works in the book so I guess thats why I called it that. The ESC module is the one in the distributor correct? The shop I took it to replaced that and the map sensor. The knock sensor should be on the intake manifold somewhere should it not? I will retard the timing a couple of degrees and see what happens.

No, the ESC module I believe (Blue Bowtie can correct me here if I'm wrong) it is on the inner right fender with the MAP sensor. The knock sensor is on the block near the oil pan rail on the passenger side - it replaces one of the cylinder block water drain plugs.

Well it seams that it was the timing that was off. I only retarded it slightly and the rattling seams to have gone away. You think the shop I where I took it would have checked the timing on it before they gave it back to me after having to for 4 days diagnosing a back firing problem but oh well. Thanks for all the help guys.

Well it seams that it was the timing that was off. I only retarded it slightly and the rattling seams to have gone away. You think the shop I where I took it would have checked the timing on it before they gave it back to me after having to for 4 days diagnosing a back firing problem but oh well. Thanks for all the help guys.

Did you put a light on it, or did you "do it by ear"? If you put a light on it, you MUST disconnect the 4-wire connector on the distributor while making the adjustment.

Yes I did disconnect the 4 pin connector, I did a search on the forum here and found a post on exactly how to do it. Thanks for your help silicon212.