Part throttle detonation

hytorksc

Registered User
I seem to be revisiting this problem again after i though i nabbed it. Maybe it's the winter time gas mix. Question: Can old worn out fuel injectors cause part throttle detonation? My SC runs really good otherwise- no other drive ability issues. My fuel system including the pump is healthy, it's at 52 psi at idle and 62 psi under load and i don't have EGR. At first i thought it was the MAF, i put the stock one back on and it still pings.

Any suggestions?

thanks-
 
Does anyone have advise on this?

Can I eliminate my part throttle detonation by installing fresh, new fuel injectors, assuming the fuel system is otherwise healthy?

thanks-
 
I should think that if the injectors are incapable of delivering adequate fuel then a resulting lean condition could cause detonation. I would think other symptoms would appear if they were this bad however, such as leaking & rough idle.
 
Digitalchaos-

You've got it exactly right! My SC does has a rough idle just after a warm start, but it goes away about a minute later indicating an injector leak. I also noticed that i don't get part throttle detonation consistently all the time which tells me that there is an intermittent problem with fuel delivery. Fuel pressure is good and i'm not having any other major drive ability problems. The car runs very strong.

What kind of drive ability improvements should i expect if i replace all the injectors with new ones (30#ers)?
 
I am thinking that if you have part throttle detonation, it is at full throttle too but you just can't hear it. The only things I can think of that would cause it is, knock sensor, bad gas or injectors and hot weather, even with an od pulley you shouldn't hear it.
 
Try a couple bottles of injector cleaner before replacing the injectors. I doubt it will fell any different if you replace your injectors with ones that are the same size.

Why not go up to 36# if your going to change them. BTW, why are you running such high fuel pressure ?

Increasing the fuel pressure will only work on a temporary basis to provide more fuel, because the adaptive feature in the EEC will slowly dial the extra fuel out. If it's been more than a couple months since the battery has been disconnected, you may want to try doing that first. Doing so will reset the EEC and provide more fuel again.

Leave the negative cable off for ten minutes to reset it.

David
 
I have a question about the pressure for you. How does the EEC know to dial back pressure? How does it know that pressure is up if the car is getting the right amount of fuel?
 
Fuel injectors are probably the least likely problem, and most difficult to check, so don't start there. Start with the easy stuff first. Have you done KOEO and ER tests, any codes? Use a DMM to directly check sensors that effect the fuel system - MAF, TP, ECT, ACT, O2. Any of these could cause a part-throttle lean condition and detonation. You have to check directly because sensors can go bad without causing a code.

BTW, "52 psi at idle and 62 psi under load" sounds way too high! How was that measured?

Aaron - the EEC doesn't dial back pressure, it lowers injector pulsewidth to compensate for the extra fuel pressure while in closed-loop mode (this is Short Term Fuel Trim). Over time, the Long Term Fuel Trim table is updated with short term values to provide correction in all modes.
 
To Rob Noth

I used a standard fuel pressure gauge and those were the readings i got. I measured static fuel pressure at 52 psi. Then i measured again while driving (load) at 62 psi at WOT, unless i read it wrong or the gauge was broken. I did recently repaired a gas tank leak (re-sealed the o-ring) and cleaned the fuel pump- maybe that had something to do with it.

It's possible that my FPR is not working correctly- perhaps that's why i'm getting 62 psi.
 
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To Dave Neibert

I always thought that with stock calibration you can't use larger injectors and expect drivability to be the same. My C&L MAF setup is for the 30# injectors. Are you saying that i should upgrade to 36#ers with the tube that goes with it? Will this improve anything?
 
last night

I switched my 5% OD pulley for the stock one to see if the pinging would go away. It did-
But i don't think you should have to do this just to eliminate pinging. It's just a 5% pulley. But then again, that heavily ported supercharger is pushing in 16 psi at 4000 rpm with a slightly modified stock exhaust (perhaps heating up things too much- clogged cats?- intercooler too small?)
I mean the car still runs fantastic from low end to high end (runs out of breath above 110 mph in "D").
 
Are you saying that i should upgrade to 36#ers with the tube that goes with it? Will this improve anything?

Yes it will supply more fuel. While your at it, you should install a new fuel pressure regulator. The pressures your getting are way too high. You need to figure out what is wrong before making any upgrades.

To measure static fuel pressure, you have to remove the vacuum/boost refrence line from the fuel pressure regulator. With line off the pressure should be 39-40 psi. With line on and engine idling you should be seeing something like 32-35 psi. For every pound of boost added the fuel pressure should increase a pound. So if you seeing 10 pounds of boost you should see 50 pounds of fuel pressure.

You can also test the static fuel pressure without removing the vacuum line and without starting the car, if you have a service manual that shows which wire from the EEC test port if grounded will keep the fuel pump running more than a couple seconds.

If you also provide a list of your mods it would be easier to tell if you are at the point of needing more fuel.

David
 
Here's my complete mod list (bolt on and custom)-

removed air silencer
fabricated an air director (a piece of plastic curved upward to the enlarged hole leading to the air box)
modified stock air box (enlarged inlet thru frame, moved MAF 2" closer to TB for better metering and lessen stock box flow restriction)
k&N panel filter
C&L 73mm MAF w- 30# tube
custom 3.5" intake made from pvc plastic
BBK 70mm TB, trimmed butterfly shaft
inlet to stock intake plenum port matched
intake plenum outlet port matched and enlarged
enlarged sc inlet
significantly enlarged sc outlet vee
MP raised top, enlarged throat
800cfm IC fan
port matched intake to IC tube
5% OD pulley from sc performance (kinda weighty)
new cheap all copper radiator with a high cfm 16" fan
cooling fan wired to run all the time
torquemaster spark plugs (jury out on this one, improved high end performance)
3pc set of underdrive pulleys
ported stock exhaust collectors
slightly enlarged resonator outlet (not much)
octane plug still connected-
moved DIS module to passenger side firewall and grounded it (eliminated quirky hot start issue)
0w-30 mobil 1 synthetic oil

everything else is stock.. i think i'm close to 300hp and definitely near 400 ft lbs at the shaft. 0-60mph in the 5's, and mid 14's.
 
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