Detonation suspected! (1 Viewer)

Joined
Jun 26, 2004
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I hear what seems like detonation.

A little history, I have done a bunch of work to this engine. Front crank seal, oil pump seal, dist seal, new wires, plugs, cap, rotor, valve cover gasket, spark plug seals, all vacuum hoses.
PAIR and EGR delete. TB cleaned along with intake manifold. O2 sensors good, 1 new one. Injectors cleaned and flow checked by local shop installed with all new seals.

Base timing as per fsm set to 3 degrees.

TPS, when set where it use to would cause about 800 rpm idle. When I adjusted it just a bit it idles at 650!

I set the base timing to 0 and still sounds like detonation.

What I am hearing: at about 1500 when accelerating I hear a not loud subtle rattling sound, rapid in pulse. If I slowly apply throttle I can increase speed and not hear the sound, but if I put my foot into it the detonation returns, so it’s a load related sound and not a RPM based sound.

Reading the FSM to adjust the TPS they talk about applying vacuum to the “throttle opener”. Where is or what is this? I see a dashpot but throttle opener?

Any ideas? Thanks!
 
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TB cleaned along with intake manifold. O2 sensors good, 1 new one.
A little off subject, but anytime I've worked on an engine that runs O 2 sensors is pairs, that have high mileage on them, and you have one of them that fails, or starts to develops issues, I've always replace them as a pair. YMMV
 
Joined
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Messages
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Location
east coast Canada
A little off subject, but anytime I've worked on an engine that runs O 2 sensors is pairs, that have high mileage on them, and you have one of them that fails, or starts to develops issues, I've always replace them as a pair. YMMV

When I first drove it after the work and had the cel, code was aft bank sensor. I measured it and sure enough it was dead. Front bank checked fine as per fsm.

Is it possible to have put the dist in off one tooth and still get it to time at 3 degrees? Then the computer is unable to correct once under load?
 
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So I pulled the distrutor, but first I set it to TDC #1 and the rotor was where it is supposed to be.

However this is an aftermarket distributor and it does not have the chamfered tooth like the OEM unit.

There is a dot on the dist gear though. When I line dot up with the dist body mark it is not pointing at the same position as the FSM shows. It points at #5! Great! But when I slide it in and rotate body to engage gears it lines up with #1. I marked dist before removal and it lines up with that mark when timed 3 degrees with the procedure in fsm.

However when I rapidly race engine from 1200
To 2500, pulsing the throttle I get the sound I am hearing, sounds like it is coming from catalytic area! I am going to pull it all apart there and reseal!

There is no CEL and no codes stored, I followed the FSM procedure.

Fawk me! So it may not be detonation after all...

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Last edited:

ppc

M Go Blue
Joined
Aug 18, 2003
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Nashville, TN
However when I rapidly race engine from 1200
To 2500, pulsing the throttle I get the sound I am hearing, sounds like it is coming from catalytic area! I am going to pull it all apart there and reseal!

That sounds like the PAIR valve is functioning like it should be doing.

As far as timing goes, you should be setting it with a timing light. As long as you have jumped the connectors in the diagnostic connecter to place the
ECM i n base mode then timing is just a mechanical adjustment of the distributor.
 
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So cats removed and when I look through them I see plenty of light. So they are not plugged and no holes. I think they are the original cats and have the TEQ stamp on them.
But it looks like the downstream gaskets were leaking a small amount and maybe the new gaskets on the front, which were leaking badly, once replaced made the rear gaskets reveal their leaks?
Gonna re-seal and test drive.:meh:
 
Joined
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Well that did nothing :bang:

Good news is I don’t think it’s detonation :clap:

I managed to replicate it in the garage, it’s more like a high pitched squeak and it definitely is coming from the exhaust area around the head pipe to cat connection. I have plates where the O2 sensors use to be as I put those in the PAIR holes.

Maybe tomorrow :meh:
 
Joined
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east coast Canada
Problem solved :steer:

Drum roll please.....I did the O2 sensors in the PAIR holes on manifold. I have a rule, if you did something and it caused a problem simply undo what you did:bang:

Okay, lots have done the O2 relocation and I have never read the issues that I was experiencing so I went through a step by step troubleshooting process. Rule one is always do the easiest, and that’s what I did when it came to a suspected detonation experience, especially with a engine with 285,000 miles.

When those did not resolve the problem I I decided to step away, relax with a GandT and sleep on it. I woke at 0700 and decided to reverse the O2 sensor mod. And it worked!!

Now I have the whistle that I have read about and I am fine with that.

Here is my theory, the O2 mounts on the down pipe is about 3/4” high, this vacant space with the O2’s removed caused turbulence which caused the noise.:meh:

It’s gone now so I am super happy, sorry for long winded reply but I have a big dislike for people who start a thread and it goes dead with no resolution, those should be deleted IMOP.

Cheers
 

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