Detonation

Paul Perreca · Dec 12, 2005

My car is running really lean, found out when we changed the spark plugs yesterday - today, i kept the windows up n gunned it, and heard some "pinging" maybe detonation, can running too lean cause detonation? I would think so - but not sure, and how can i adjust the fuel pressure w/o a guage to up it - i have an adjustable fuel pressure regulator - and get this, 5.0 magazine has an article that says you don't plug the vac line when you take it off, leave it open to the atmosphere and you will lose approx 4-5 lbs pressure at WOT or something of the sort -
THANKS
Paul Perreca

2002BLGT · Dec 12, 2005

Paul Perreca said:
My car is running really lean, found out when we changed the spark plugs yesterday - today, i kept the windows up n gunned it, and heard some "pinging" maybe detonation, can running too lean cause detonation? I would think so - but not sure, and how can i adjust the fuel pressure w/o a guage to up it - i have an adjustable fuel pressure regulator - and get this, 5.0 magazine has an article that says you don't plug the vac line when you take it off, leave it open to the atmosphere and you will lose approx 4-5 lbs pressure at WOT or something of the sort -
THANKS
Paul Perreca

that doesnt even make sense , the reason you pull the vacuum is to get a WOT reading so pluging the vacuum hose does nothing to change the setting ....it only helps keep the car running smoothly while you are adjusting things ......when you unhook the vacuum from the regulator you have 0 inches of vacuum , just as if it were at WOT so how would plugging it or not plugging the vacuum affect anything to do with the regulator .... you need to go by a fuel pressure tester from a local parts store ....they cost about 35-40 bucks and are well worth the money ....

Paul Perreca · Dec 12, 2005

yea i dont know how that makes sense lol I just read it - but neway, do you think that is my detonation problem? the leanness?

2002BLGT · Dec 12, 2005

Paul Perreca said:
yea i dont know how that makes sense lol I just read it - but neway, do you think that is my detonation problem? the leanness?

what plugs you running and what is your timing at ?

HISSIN50 · Dec 12, 2005

Paul, running lean can definately lead to detonation.

I read that same blurb IIRC and the difference was that they simply choose not to plug the vac line when they remove it. Removing the line simulates WOT (zero manifold vac) and the pressure does go up by 4-8 PSI.

Now they simply have a slight vac leak goin on by not plugging the line. This theoretically raises the idle a hair, which leads to a tiny difference in the setting compared to how most of us recommend setting it. It is not worth worrying about at all IMHO.

You really should get a gauge of some sort so you can see what is going on. I am not one for permanent under the hood FP gauges, so I just use the diagnostic gauge when needed.

Good luck.

Paul Perreca · Dec 12, 2005

plugs installed yesterday were the autolite 3924's requested by 99% of everyone on here that replied to me w/ aluminum heads - so i listened and got them - timing has never been set - no idea

HISSIN50 · Dec 12, 2005

Paul, you gotta check that timing. Too much advance can lead to detonation as well.

2002BLGT · Dec 12, 2005

timings the problem , that and probably dont have enough fuel pressure in it ...but timing will affect it above all else

Paul Perreca · Dec 12, 2005

yea i never even checked it cuz when i put the light on it to check it, the numbers on the balancer were painted black and i couldn't read them -

than we had to do somethin else n never got back to it

Curse · Dec 12, 2005

Paul Perreca said:
yea i never even checked it cuz when i put the light on it to check it, the numbers on the balancer were painted black and i couldn't read them -

than we had to do somethin else n never got back to it

Get timing tape, it will make reading the timing a lot easier. Also get a reading on your fuel pressure. Some AFPR are not set right out of the box, so who knows what your FP is set at.

Black1987Stang · Dec 12, 2005

Paul Perreca said:
- timing has never been set - no idea

Go check that right now lol Dont want to ruin that nice new motor you got there I have an excuse about mine, since mine says 65 degrees advanced Ive been tuning the timing by ear which isnt exactly the best but cant find out my problem ever since i put my new motor in soo its gonna have to stay like that till i find out whats wrong

Paul Perreca · Dec 12, 2005

yea i guess we kinda timed it by ear, so it's not gonna hurt, just might not be getting all the performance out of it, or it could be off enough to cause the DET

HISSIN50 · Dec 13, 2005

Paul Perreca said:
yea i guess we kinda timed it by ear, so it's not gonna hurt, just might not be getting all the performance out of it, or it could be off enough to cause the DET

Paul, man you gotta clean your ears. The whole point of 'timing it by ear' (which we all do) is to back it off if pinging is heard.

sgarlic · Dec 13, 2005

Maybe your car is like mine was.. detonated at anything over 9*

Just borrow a timing light from somebody.. it's simple.. use chalk.. just check it!

Black1987Stang · Dec 13, 2005

White out works even better

HISSIN50 · Dec 13, 2005

I use a silver sharpie marker on black balancers. Seems to hold up well.

DMAN302 · Dec 13, 2005

Paul I'd follow JT's advice..get a timing light on there pronto!..detonation is really NOT good for the engine and it's something you want to take care of early. Remember when you asked me what was on the cowl of my hood...well that was a fuel pressure gauge, it may not look pretty sitting up there, but it's a tuning tool for me and IMO you need on somewhere on that car. When running a modified car like you are you need to "fine tune" some things inorder to keep it running correctly and safely for the motor...GET ER DONE.

Paul Perreca · Dec 13, 2005

i can't just back it off by ear cuz it only detonates when at full throttle.... so i will just not floor it till i figure this out

DMAN302 · Dec 13, 2005

My father refers to such methods as half assed...I suggest you take 5 minutes and do it right, nothing but good will come of putting a timing light on there.

Black1987Stang · Dec 13, 2005

Yea and theyre like what 20-30 bucks from autozone or something? Its well worth it anyways

Detonation

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