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3 DEG SPARK


adallak

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I am chasing hot engine knock under slight acceleration. It sounds like a spark knock. I ran diagnostic today and snapshot data showed 3 DEG SPARK . I know it should be 10 DEG.

Can the car run OK with 3 degrees instead of 10? Unfortunately, I do not have a stroboscope to check the timing directly.

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Sounds like poor EGR flow causing detonation. It took me a long time to fix and I would not get rid of it unit I cleaned the hell out of the EGR ports in the TB, replaced all vacuum hoses and replaced my EGR. Don't overlook the EGR system when you get light pedal detonation.. If you do a search under the old archives for light pedal you will find my thread...

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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I am chasing hot engine knock under slight acceleration. It sounds like a spark knock. I ran diagnostic today and  snapshot data showed 3 DEG SPARK . I know it should be 10 DEG.

Can the car run OK with 3 degrees instead of 10? Unfortunately, I do not have a stroboscope to check the timing directly.

If those readings are correct, and I understand what you're saying, it's seven degrees retarded. That condition will help reduce 'spark knock' (detonation). Advancing beyond (greater than) 10 degrees would increase the probailities for detonation.

'93 STS.. opened, dropped, wide...fast.

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Sounds like poor EGR flow causing detonation. It took me a long time to fix and I would not get rid of it unit I cleaned the hell out of the EGR ports in the TB, replaced all vacuum hoses and replaced my EGR. Don't overlook the EGR system when you get light pedal detonation.. If you do a search under the old archives for light pedal you will find my thread...

Scotty, I saw your post as well as many others concerning 4.9 detonation. Checked and rechecked , cleaned all the tubes, TB and passages... no luck... The only thing I did not touch was the EGR valve itself. It might be the culprit... I remember a post stating you cannot check the EGR operation while idling in Park. Is it true? I do not have an assistant at the moment to put it in D or R....

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QUOTE (adallak @ Apr 26 2005, 05:53 PM)

I am chasing hot engine knock under slight acceleration. It sounds like a spark knock. I ran diagnostic today and  snapshot data showed 3 DEG SPARK . I know it should be 10 DEG.

Can the car run OK with 3 degrees instead of 10? Unfortunately, I do not have a stroboscope to check the timing directly.

If those readings are correct, and I understand what you're saying, it's seven degrees retarded. That condition will help reduce 'spark knock' (detonation). Advancing beyond (greater than) 10 degrees would increase the probailities for detonation.

Bob D, so the computer takes 10 degrees as a reference point? If so, 7 DEG is just what the doctor ordered for 89 octane. But I had the same knock when I used 93....go figure.

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I was thinking like you that it was pre-ignition or spark knock that it was related to overheating, low octane, or a distributor that was too far advanced.. It ended up being EGR flow, pull your EGR and clean the heck out of it, and see if you get any difference. I have been told that they are hard to clean and its best to replace them but you may have someluck.. Guru will chime in on this, he was a huge help to me

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Thanks bbobynski for the instuctions.

The tubes are clear - I can see the bottom edges of both of them and through tem the bottom of the TB. The two passages from TB to solenoid and EGR valve are claera as well. The only thing I did not like is that the smaller tube was kind of loose I could move the top about 1/4"... The big tube was OK. I'll check the EGR valve as you described, no helper unfortunately at the moment.

I never played with timing and pretty the setting is original. As I said the octane does not make diference - I get the same knock with 89 and 93....

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The tube being loose is normal.

It sounds like the EGR may not be getting vaccuum to the solenoid or the solenoid is not activating when commanded by the PCM. If you have a vacumm guage you can tee it temporarily into the vacuum line between the solenoid and the valve and drive the car. YOu should see vacuum to the valve when the throttle is opened with the car in gear....or, if the engine is warm, just do a gently brake torque in drive and you can see the vacuum signal

bbobynski,

Here are some inconclusive results since there is no neither helper nor vacuum gage.

1.There is vacuum to the EGR solenoid from the TB (loud hiss) while idling.

2.There is no vacuum after the EGR solenoid while idling (which is good).

3. Disconnected EGR solenoid to open it fully - there was barely noticable vacuum after the EGR solenoid, no hiss just barely noticable vacuum which is I BELIEVE is not right, since that low vacuum cannot drive the EFR valve IMHO.

4. Have bypassed the EGR solenoid and attached the vacuum hose from the TB directly to the EGR valve. Drove the car with engine hot (more than 200 degrees under load) - NO KNOCK!

The only conclusive result so far is that the hot knock was really spark knock and full vacuum supply to EGR valve enabled enough exhaust volumes to the combustion chamber to cool it down and prevent detonation.

Inconclusuve result are that:

1. The EGR solenoid probably does not work properly since even being disconnected did not provide noticable vacuum to EGR valve (REALLY WEAK) or compareable vacuum to one from the TB. Here may be some electrical problem (unlikely) or just deffective solenoid. It measured 33 Ohm which is within specs though.... And the test light connected to the hurness cycled while in diagnostics as it should have done.

The EGR valve works most likely OK though may need some cleaning. The two bolts are unreachable without a special wrench so I left the EGR valve cleaning for future.

Does these results tell something to you, or all this just waste of the time?

As always your input is highly appreciated!

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Another observation - the EGR solenoid's input has very small diameter something like 0.5 mm. It means EGR valve should be pretty sensitive device which makes it very vulnerable to failures because of carbon deposits in all kind of locations such as EGR tubes, passages and the valve itself as well as vacuum leaks and obstructions in related hoses. Looks like serious attention to the EGR system should be paid even in absence of related codes such as ECM 48 for 4.9 engine.

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Sounds like you are getting there Adallak

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Sounds like the EGR solenoid has failed....or the wiring to it is damaged. You can cycle the EGR solenoid in the PCM output cycling mode of the onboard diagnostics...or....just replace it.

The vacuum to the EGR valve is restricted to allow the vavle to control by "leaking" vacuum internally. The backpressure transducer inside the valve is a mechanical pressure transduce that controls the vacuum bleed inside the valve to control the height of the pintle valve.

I would say that from what you have done that the EGR solenoid is failed and needs to be replaced. That is what I would do at this point.....

Nice job on the diagnosing.

Thank you, Bbobinsky for the reply. I have planned some additional test while I am on EGR system. Yeah, looks like the solenoid needs to be replaced. It is not in my short list though.

Scotty, my alternator started whining... Looks like the bearing you have given me was right in time! :lol:

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