Bone stock car knocking on load
 

Hi everyone. I bought a 93 LHD touring model. When I bought it I noticed it knocked when I put my foot into it. I figured it was the old fuel and forgot abbot it.

I've since run 2 tanks of 91 through it and it still does it. I don't think it's the fuel.

And I can't adjust timing on this engine. SDI what an I left with?

Fuel filter? Fuel screen if any?

Not sure what wise it could be. The engine is 5000km old, built at Mazda. Boost pattern is correct. Runs perfectly side from a small stumble when accelerating lightly around 2000 rpm.

Should I check my tps? Anyone know the readings I need offhand?

Its unlikely to be knock and more likely to be the age old 2500-3000 rpm hesitation. Scholars have been trying to solve it for years with no luck, and they maintain blaming it on gremlins. Search the forum and you shall find.

I can hear the knock. Sounds like marbles for a split second when I hit it.

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I agree that is unlikely to be knock. I would first check the spark plugs, then the spark plug wires to make sure they are all in good condition.

My mechanic once described detonation as "sounding like marbles" so thread lightly

It's definitely knocking, the car runs perfectly, all wires are giving spark. the plugs are 5000km old.

you can hear it clearly through the firewall. I dont put my foot into it anymore because of this. does anyone have any insight?

Checked TPS, sitting within spec. I'm officially lost now.

(green wire with red strip) Closed throttle +V range is 0.75 to 1.25. Fully open throttle +V range is 4.8 to 5.0.

(black wire with green strip) Closed throttle +V range is 0.1 to 0.7. Fully open throttle +v range is 4.2 to 4.6.

every time i've seen a stock FD knock, its been a bad plug wire. not sure why that makes them knock, but it does.

the wires need to be the correct type, the resistance spec should be in the FSM. you also may wanna make sure the wires are on the coils all the way, people screw this up all the time/crap wires fall off.

next step is to make sure it has the correct plugs in it.

if it still does it, you might wanna check that the fuel pressure regulator vacuum line is hooked up correctly, and then maybe you need fuel filters. there is a sock in the tank

Very weird that a lack of spark would cause knock.

So i guess i should add plug wires and plugs to my list.

- Fuel filter
- Plug wires
- Platinum plugs, heat range 7 leading, 9 trailing.

it might be a cross fire, for sure i've seen more than one wire set installed badly...

That's an interesting idea. the engine was replaced 5000km ago at the mazda dealership in Vancouver. It didn't cross my mind because I assumed Mazda would know how to do something as simple as plug wires, but i'll have a look at that as well when i do the plugs.

make sure the leading coil is going to the leading plugs. I flipped them once replacing the plugs and the car knocked like your describing. Also check the condition of the leading plug, I know from experience the knock sensor reads higher when the plugs are worn

ok, so i took a look at the plugs and wires today. Everything looks like it was replaced when the new engine was installed 5000km ago. The plugs are a nice dark brown, looks like good even combustion

The plugs are in the right places. BUR7EQP Leading (bottom). and BUR9EQP trailing (top). Plug wires are going in the right places as per the attached picture.

All 4 wires show good continuity, and almost exactly the same resistance.

and they were all the way on the coils?

Yes, I felt the clips as i pulled them all off, then all clicked back into place nicely when pushed firmly.

Tried filling up with 94 octane from an empty tank, still some knock at wot.

this thing is starting to make me upset. would be a shame to blow up a brand new engine.

Just taking a shot in the dark, but maybe a clogged injector?? Do you know if they have ever been cleaned? Try running a can of BG44K in your gas tank.

Did you ever change your fuel filter and pull the pump to make sure things look okay in there?

Not sure if they have. Brand new engine though. I'll try some fuel system cleaner. No idea what the stuff you mentioned is.

No I haven't done the filter yet. Don't I have to drop the tank to get at the pump?

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BG44K is a high quality injector cleaner that mixes with your fuel in the gas tank .

There is easy access to the fuel pump from the rear cargo area behind the drivers seat.

The stock plugs run a lot of gap. About .060" if I remember right.
I found that a HKS Twinpower was the best addition to a nearly stock (and up to 550 hp) engine.
It is easy for the spark to blow out with boost and a wide gap.

Could the pick-up coils have their plugs reversed?

You might try to decarbonize the rotors... maybe you have a buildup of carbon.
Chevron Techron is a great injector cleaner but also cleans internal carbon buildup.

Also, do people still use Seafoam as a cleaner?

Some thoughts,
Barry

oOOo since the engine was just out, this is a good candidate

post a sound clip if you can

I had a loose center on the OE clutch disk which sounded similar when I first bought my FD. It also lasted only short time during accel and then would go away completely. But mine was only when accelerating in second gear.

I thought it was detonation and looked at everything I could including performing a crude version of an injector pressure drop test. Finally got to the point I concluded the running of the car was fine. After a while the disk started rattling at idle which made the diagnosis easy.

Anyway, rattling clutch disk a possibility to consider.

No it isn't. The car wont run with the pickups reversed.