detonation in third gear????

[mysvo71]

hello,
My 86 seem to detonate in third gear. I've been through the all the tune up steps, checked fuel pressure, and even put in new injectors. But with all of this it still seems do baffle me. any help will be greatly apriciated.
thanks

[SVOeric]

what ignition timing are you running, and is your knock sensor hooked up?

[mysvo71]

10 deg, knock sensor hooked up.

[SVOeric]

interesting.. normally the knock sensor is very sensitive to knocks, and pulls timing enough to keep that from hapening.

are you sure what you are hearing is detonation?

what rpm range is it starting?

the next place I can think to look would be the vAM, possibly letting in too much air ??

[svobud]

ok....how bout - what's your set up? Stock or modified? stock bcs manual adjustable boost valve? If so, the psi setting? fuel pump? stock or not? fuel pressure regulator...stock or not - and what's the psi? helps a little more when you explain to us what we're looking at instead of 'it's detonating in 3rd gear (only?) even with the knock sensor hooked up...know what I mean? Btw, when was the last time you changed your fuel filter?

[SVOeric]

ugh.. too many similar posts, I thought he had already said most of that stuff...
:)

thanks Bud, for asking the right questions..

[mysvo71]

definatly detonation! starts as soon as i shift from 2nd to 3rd.(3500+) seems to be at the point of highest load. also to much air??????

[mysvo71]

car is stock all but a K&N filter. has 40lb at idle and with a guage hooked up presure seems to stay right at 40lbs and replaced the fuel filter 4 2 months ago.

[SvoTy]

Originally posted by mysvo71
car is stock all but a K&N filter. has 40lb at idle and with a guage hooked up presure seems to stay right at 40lbs and replaced the fuel filter 4 2 months ago.

A couple of things to look at.

Your fuel pressure should climb by 1 pound of fuel pressure for one pound of boost.

If you have a 40# base pressure, and add, say 15 pounds of boost the pressure should rise to roughly 55 pounds.

Also you need to pull the plugs and look at them to see if one injector is leaning out. That is the problem that I had with my car not too long ago.

The #4 injector was weak and the # 4 plug was a nice white compared to the other 3 that were tan.

This is kind of a hard thing to diagnose over the internet. There are so many more varibles from sensors going out to oil finding its way into one cylinder.

Just take your time and check things out one by one and you should find it.

[GT350R]

Originally posted by SvoTy


A couple of things to look at.

Also you need to pull the plugs and look at them to see if one injector is leaning out. That is the problem that I had with my car not too long ago.

The #4 injector was weak and the # 4 plug was a nice white compared to the other 3 that were tan.



Exactly the advise I was going to give!

[mysvo71]

thanks guys for all of your help. I'll go back through and check everything again and see if I can fix the problem.
thank again

[ccst stang]

ive had the same problem and i cant figure out what it is
any help for me?

[NavySVO]

Originally posted by mysvo71
car is stock all but a K&N filter. has 40lb at idle and with a guage hooked up presure seems to stay right at 40lbs and replaced the fuel filter 4 2 months ago.
40 psi.........is that with the vacuum line connected, or disconnected to the FPR? It should be around 38-40 disconnected when checking base (idle) fuel pressure.

ive had the same problem and i cant figure out what it is, any help for me?

read the advice and ideas given to mysvo71 then get back to us.

[SVOeric]

check the dates on the posts -- that post you replied to was from 2002...

ccst stang -- Read the question Bud asked -- that's what we would need to know.

[NavySVO]

Doh!:tomato:

[under pressure]

I know it's an old thread but it came up in the search for fuel pressure. I adjusted my fuel pressure to 40 psi. I taped the F.P. guage to the windshield and went driving to check WOT pressure readings. I'm running a hair into the red on my stock boost guage. I figure 15-16 lbs of boost. My engine has a ported 86 head & cam, cam set at 0*. ing. at 9*, brown injectors, PE computer, .63 turbo, no cat. 255 lph FP. I replaced a leaky injector. It's flowing a lot of air. I pulled 52 lbs. the first time. I turned it up a 1/2 turn on the AFPR it went up to 54 lbs. The engine is not missing on the top and is pulling stronger. It use to hit a flat spot above 3500 rpm. I noticed at 54 lbs on holding the pedal at WOT the pressure backed off about 2 lbs. I'm going to turn it up so that at WOT I've got 55 lbs. minimum. I also used the Shell V-Power high test and added about 1 qt. of Touline so I've got good octane. After I get the WOT set I'll check the base setting which I think might be around 43 psi or higher. The base setting is one thing but I'm going by WOT from now on. I won't be running WOT 99 % of the time but if Eric pulls up next to me at the light I'll need that extra 1 % of V-Power! Don't make me do it Eric! Rick