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Old 07-17-2005, 01:54 AM
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*** 383 Sparking Problem 2500 RPM under pressure

Hello!
I'm still having problem with this New Engine.

I went to my tuning shop and he checked my engine with Sun MCS.
All the 8 cylinders are o.k.
The carb and fuel system is also fine.

The engine starts back firing when in 2nd or 3rd gear, around 2000-3000 rpm.
When under load.
And this happenes when the engine becomes warm. Not when cold.

So the tuning shop told me that this is a very small electricity cut off.
He sujested that I change my Ignition Key, Because he has experienced this problem to be from worn out ignition keys!

Can anyone help me on this? It's becoming a pain in the ***!
I haven't run the engine for even 50 miles, and like this can't break in the engine!

Thanks,
Houman SS '70

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Old 07-17-2005, 04:57 AM
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Quote:
when the engine becomes warm. Not when cold.
what octane fuel?

flat top pistons?

what cc heads?

what size carb and more specifically jets & power valve?

are these new plug wires new?

pull your plugs and run an AC44 or AC45 for now.

are you sure the rockers are set correctly?

have you ran a compression test when cold vs warm?
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Old 07-17-2005, 05:28 AM
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Thanks NXS for your reply.

Actually, I have Edelbrock RPM Heads 64 cc + 4 relife flat tops ( 345np) + Fel Pro 1003 0.49" thickness + 1.5 ratio rockers + Holley 600 CFM DP + Lunati VOODOO 219/227 @ .50 & .468/.489" lift.

I use 95 octane ( as claimed by the gastation) but I anyway pour 1 octane booster in the tank.

I have Accel 8.8 wires + Splitfire Triple platinum TP 392 c.

All the above are brand new.
First day when I got the car out of garage to take home, I faced this problem after getting stucked in Traffic for a while, when the engine got warm.

When, I got home I called my Mechanist and he told me to check the plugs or wire boots in the dark to see if there are any bad plugs or bad wires there. So I did it and I say #1 and #7 glowing in the dark.
But actually I pushed those boots further in and I don't see any spark glowing around those two plugs any more, but the problem still exists. So I thought that the problem was somewhere else.

Now NSX, I have not run a compression test, for two reasons. First is that I don't know how to do it?

Second is that, as you know and we spoke earlier, I'm in Iran and we don't have such tuning specialist for hi performance car and specially for V8's.

What do you suggest? And why do you think that the SUN tuner/scanner didn't show anything?

Thanks for your comments.

Houman SS '70
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Old 07-17-2005, 05:39 AM
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FPP 1003 is a .041" head gasket

That is just over 11:1 but with 95 octane and aluminum heads you should be fine.

If the vacuum advance is hooked up disconnect it and drive it.

If not bump the timing down a few degrees.

Is this under very light throttle, mild acceleration or just touching the secondaries? Does it happen under full throttle?

What jets are in the secondaries? is your fuel pump up to the task?
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Old 07-17-2005, 05:47 AM
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Quote:
Originally Posted by NXS
FPP 1003 is a .041" head gasket

That is just over 11:1 but with 95 octane and aluminum heads you should be fine.

If the vacuum advance is hooked up disconnect it and drive it.

If not bump the timing down a few degrees.

Is this under very light throttle, mild acceleration or just touching the secondaries?

Does it happen under full throttle?
NSX, It happens mostly under mild acceleration. You when?
It happenes, when the rpm is lets say 2000 and going up hill in 3rd gear! If I wot the trans will shift back to 2nd gear and there'll be no probelm, but if I don't WOT and just put some mild acceleration raising 2000 to 2500 and sometimes to 3000, then it will have this problem.

It's like having one cylinder not working for a very small portion of a second and then working again. You know how I mean?

Thanks,
Houman
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Old 07-17-2005, 05:52 AM
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Quote:
Originally Posted by Houman SS '70

It's like having one cylinder not working for a very small portion of a second and then working again. You know how I mean?

Thanks,
Houman
Not exactly, is it spark knocking/pinging/rattling? or is it bucking/surging?
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Old 07-17-2005, 05:58 AM
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Sounds to me like a weak ignition problem. When the engine is under load is when spark energy is most important. Tell us more about the ignition system.

Chris
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Old 07-17-2005, 06:00 AM
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Quote:
Originally Posted by NXS
Not exactly, is it spark knocking/pinging/rattling? or is it bucking/surging?
I really don't know what bucking and surging means.

I know what knocking and rattling means, it's the condition when the dist. is too adv. and when under acceleration you'll have the rattling noise. Right?

If yes, o.k. my engine doesn't rattle.

You know it's like, when you have fuel shortage? You know how it is? It works and it does not work at the same time?

This is what happenes to me as well. You hear the exhaust sound changes as well. So kind of back fire. or Sniff ( as we say it here) but not in the carb. in the exhaust.

But over 3000 when the secondaries are open this will not happen.

I myself, think that it's some type of elec. shortage. But where? and why in 2000-3000 rpm? Why when the engine is completely warm?

I don't know really.

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Old 07-17-2005, 06:04 AM
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Quote:
Originally Posted by TurboS10
Sounds to me like a weak ignition problem. When the engine is under load is when spark energy is most important. Tell us more about the ignition system.

Chris
Yes Chris, at least this is what the tuning shop said as well. But he couldn't prove it

I've got Mallory HEI dist. and Coil.
Accel 8.8 wire
Splitfire TP 392c.

A freind told me that the tuning shop could be right. Because there's a ignition control under the steering column that could cause such a problem sometimes. What do you guys say?

Could it be plug gap??



Thanks,
Houman
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Old 07-17-2005, 06:13 AM
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Big cams and 4-speeds are known to do this from time to time, but your cam's not too big. Still keep it in mind.

On the HEI, is it powered by the stock wire that ran the old ignition system? It has a resistor in it to keep the voltage down to 10V or so. The HEI needs 14V.

Where id you come up with that style of plug? I like the AC45 or AC44 but I'm not sure if the RPM heads take them or not.
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Old 07-17-2005, 07:47 AM
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You can verify if this is a power supply problem to the distributor by disconnecting the stock ignition wire from the distributor, then run a 10 guage wire from the positive side of the battery to the distributor. This will provide full voltage directly from the battery to power the ignition and will totally eliminate all of the stock ignition wiring and switch. Then test drive the car. If the problem is gone you now know the problem is either in the wtock wiring or ignition switch. You'll need to disconnect the temporary wire to get the engine to quit running.

AC R42 is a good heatrange plug if you're fighting detonation with the high compression.

Another problem could be your spark advance curve, any idea what the timing is set at now? how much total advance? at what rpm is total advance? Bob
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Old 07-17-2005, 01:23 PM
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Thanks to all of ya!

Actually, I'm somehow used to Splitfire plugs, it seems that nobody really likes them over there!

Well, regarding the total advance, I don't know. Haven't checked yet.
I am using the stock ignition wiring at present, but will definitly try what you suggested.

I hope one of these is the solution to my problem.

Thanks to all.

Houman
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Old 07-17-2005, 01:48 PM
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Is the backfire coming from carb or exhaust?
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Old 07-17-2005, 11:16 PM
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56Maynard,

The backfire is coming from the exhaust!
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Old 07-18-2005, 05:59 AM
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Stock HEI can be the issue. I would get an MSD and add it to the system. Pick up a used one and it wont cost you much to try. It certainly will not hurt anything and will give you better performance even if it does not solve this issue.

Chris
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