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Old 05-01-2004, 20:34   #1 (permalink)
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detonation and regraphing distributor

I'm running a 302, C4, LPG - single Gas Research throttle body, I don't know too much about the engine specs, it was rebuilt professionaly about 3 years ago.

I've got a real problem with detonation, I have to retard the timing so much that the car's really got no go, particularly down low. It doesn't seem to make any power until about 2300 rpm. My wifes 93 Nissan Pintara beats it off the line :(

If I advance the timing up any further, it starts detonating at about 3000rpm (down to 2000rpm if it gets hot). So I leave it retarded and drive around like Granny on her way to bowls :(

When it was first rebuilt, I had it on petrol (It always detonated right from rebuild), and the guys who built it said that they had added some extra compression 'cause I said that I was going to run LPG and that the detonation wouldn't be a problem with LPG, but even with LPG now it still denotes really badly.

I've read on this forum about regraphing the distributor, would this help? Does anyone know of anywhere in Canberra that can do this? I've got the standard electronic distributor.

Cheers.
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Old 05-01-2004, 20:47   #2 (permalink)
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Re: detonation and regraphing distributor

Being a 302 it can't have that much compression.

What is the static timing?
What is the total timing?
Is the vacuum advance working?
Does the cam sound stock?
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Old 05-01-2004, 21:41   #3 (permalink)
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Re: detonation and regraphing distributor

Quote:
Originally Posted by xbgs351
Being a 302 it can't have that much compression.

What is the static timing?
What is the total timing?
Is the vacuum advance working?
Does the cam sound stock?
I don't really know what's in the engine sorry to be vague on the details.

The vacuum advance seems to be working fine, the distributor was replaced new when the engine was rebuilt. I don't know what the timing is, I just turned the distributor until it stops detonating. If I advance it up it has HEAPS more pickup down low, but detonates early.

Once again I don't know what the cam is although the shop said that they had used a "good cam suitable for gas". It was a reputable "performance" shop in Perth, I just can't remember the name of the place (I moved to Canberra). It's on the South side of Leech HWY out Kewdale way anyone from Perth know the place that I'm talking about?
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Old 05-01-2004, 22:10   #4 (permalink)
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Re: detonation and regraphing distributor

My 351 had a few probs like this, and i sent the electric xd dizzy to Melbourne to performance ignition systems(i think thats the name) and it acted like a new car ever since. My timing is 14 initial and total of 34. They also told me to leave the vacume advance disconected. As someone else said, being a 302, you can't really have too much compression if you are running flat top pistons. I would get the dizzy looked at, and maybe even cam timing. But, please check with timing light and see what it is, and where you are having problems. I bet the total is going wayyy too high. Let us know where the timing is when it doesnt detonate.
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Old 05-01-2004, 22:11   #5 (permalink)
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Re: detonation and regraphing distributor

Don't you own a timing light?
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Old 05-01-2004, 22:14   #6 (permalink)
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Re: detonation and regraphing distributor

Make sure no oils getting into the combustion chamber as it'll cause detonation. Gas hides smokey engines unfortunately. A smokey engine on petrol won't blow smoke on gas. I've seen quite a few like this.

Too much advance too early? You can bend the tabs which tighten the springs for the mechanical advance a tad. This will make the mechanical advance come in later.

Another thing it could be is worn bushings in the distributor. The shaft would slop side to side and if you put a timing light on the balancer/timing mark. It'll be all over the place.

Did the detonation just start happening suddenly? ie no detonation for the first few years then just started pinging?

Problem is with gas it they reduced the RON so all these engine built with high compression no longer liked gas. I've heard around the traps that gas is getting put increased upto a higher RON level but it could be just a rumour.

So you have a few things to do/check;

a) plugs
b) check the mechanical advance springs in the dizzy aren't too loose. Bent tabs out slightly if necessary.
c) bushes in the dizzy
d) finally have the timing properly set. You can static time it if necessary but a timing light is a better option.
e) make sure you haven't got worn guides or stem seals

To static time you turn the crank to the desired timing point. Turn the ignition on but not to the start position. Turn the distributor till is sparks. Turn it back and forward more than once to make sure your as close as possible to the point of spark/timing.

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Old 05-01-2004, 22:38   #7 (permalink)
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Re: detonation and regraphing distributor

Nah, I don't have a timing light, I'll try to take is somewhere and get the timing checked, but it has always done this right from the start. I've taken it to a few different shops and they always say that it has a problem with detonation, so they have to leave the timing retarded. When I ask about the detonation they generally just say something about compression, or bad fuel and that you'd have to pull the engine down to find out.
The distributor is only 3 years old so there shouldn't be any problems in there, the moving bits move freely and the solid bits are nice and tight.
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Old 05-01-2004, 22:42   #8 (permalink)
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Re: detonation and regraphing distributor

Quote:
Originally Posted by spaceman347
Nah, I don't have a timing light, I'll try to take is somewhere and get the timing checked, but it has always done this right from the start. I've taken it to a few different shops and they always say that it has a problem with detonation, so they have to leave the timing retarded. When I ask about the detonation they generally just say something about compression, or bad fuel and that you'd have to pull the engine down to find out.
The distributor is only 3 years old so there shouldn't be any problems in there, the moving bits move freely and the solid bits are nice and tight.
Don't rely on mechanic workshops. Find a decent Ford Cleveland dyno tuner to find the issue if you cant? I had pinging issues when I got my engine done. Mechanic couldn't stop the pinging but a very average dyno tuner did. I soon after went to another dyno shop and got a smoother a/f throught the rev range and picked up 50rwkw.

It won't be that hard to sort.

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Old 05-01-2004, 23:21   #9 (permalink)
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Re: detonation and regraphing distributor

don't static time it........this'll just suck you in to false point, use a light. run the vacuum advance, change your leads and make sure they're seperated properly.if it's points make sure your dwell is correct.
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Old 05-02-2004, 00:38   #10 (permalink)
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Re: detonation and regraphing distributor

make sure you don't have a vacuum leak too
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