Causes of knock in low rpms...

[89ShelbyGuy]

Hey guys...well, my shelby has been givening me a hicup with knock.

I have a flashable smec in the car with the CEL knock light activated.

I have some +20's i bought off a memeber here along with a adjustable fuel pressure regulator..set at 55psi

Most days i drive the car it drives like a beast...i've been boosting to about 17-18 psi, but on curtin days i have getting knock going threw my gears with regular city driving...no boost...i really don't think its false knock as my wideband is jumping all over the place...sometimes shooting to 17afr..

My qeustion is, what causes knock...my geuss is a fuel injector is not doing its job....could a faulty regulator cause this also? if so, how?

Last time this happened i parked the thing for a week....loaded a new cal into my smec..and the car was fine for a week....now back to the knock problem..i am sctratching my head on this one cause i am driving the car like a grandpa and i am still getting some solid knock in lower rpms...what gives...before i take the injectors out and send them out to be tested and cleaned i was going to see if any of the gurus here have any tips..

[Aries_Turbo]

could be a number of things. does it do it on hotter days more than colder ones?

i doubt its the injectors if it runs awesome when you are hammering on it.

could be a calibration setting, could be some loose stuff rattling, could be an over sensitive knock sensor etc.

Brian

[89ShelbyGuy]

The last too tips you have menstioned is not the case...muliple knock sensors have been installed....all the rattling stuff has been quadrouple checked..

As for when it happens...more on humid days i geuss...And also, when its acting up, i can't do WOT runs cause theres always knock..and the days that its doing it, i am getting blips of running lean...from 10.9 to 12.xxx but ofcoarse the knock light won't come on then...

I am going to reflash the smec today and see if that takes care of it...last time it did..


btw...when you flash the new cal, how long does it take the computer to relearn everything?

[RoadWarrior222]

Well if it acts up on damper days then I'd be checking fuel pump grounds/connections.

[89ShelbyGuy]

Yea i thought of that, but this last time is started doing it, i already had driven it over 20 miles without issue...then just before i got home, it started doing to knock crap....if it had happen after it had sat all night...yea...i could think some moisture is getting somewhere..

[89ShelbyGuy]

Well, just re flashed the calibration...no dice...still the same crap.

I don't understand the wideband though...i was in 2nd gear...going bout 2500-3000 rpm...anytime i jam the pedal..it instantly goes down to 10.9 or below no knock.....i then shift into third...and do the same thing, but knock light comes on and the wideband still is shooting down to 10.9....if the engine is seeing knock...would i be running lean?

Could a faulty Adjustable Regular be causing this?
Could a injector that is somewhat clogged and not giving a good spray be causing this?
Could my IAT sensor be causing this if its faulty?

The things i did in order last time i had this problem are the following:
1. Pulled negative cable off battery and removed smec 60pin connector and checked conutinty(sp) between the knock sensor and the pin on the connector...that was fine.
2. pulled the IAT sensor from my intake (re routed it to front of car) Check resistance on that...had a crappy tester..not my fluke...guessing it was ok....but the plastic on the sensor was in ruff shape...thought i had a different one...but didn't...so re installed....
3. Re flashed a new calibration

Started the car and went for a drive...no problems..runs great...drove it for the week almost everyday....then yesterday..coming home from an arron...and there goes my knock cel....which leads me to today.

[GLHNSLHT2]

so does the CEL just turn on while just cruising? or is it always after a shift? Does it stay on and run like crap?

The IAT sensor doesn't even work right in T-smec right now.


My daytona would flash the CEL on a shift sometimes even though I was plenty rich. It'd retard the timing too. I don't remember if I ever checked knock voltage when it did. That was using Rob's old T1 based cals. But it would just flash and go out. but it was enough to bog the car on a shift.


Then the car would flash the CEL and retard timing if I switched from low to high beams. Never could figure out why it would do that. but it did.

[89ShelbyGuy]

It turns on while cruising.......sometimes its just a blip (i hooked up a little buzzer to the cel so i hear it rather then see it) and sometimes it will stay on for 5 seconds then go off. The car runs fine when this all happens...

---------- Post added at 10:30 AM ---------- Previous post was at 10:28 AM ----------

On thing i do notice when this crap is happening is my wideband is all over the place....will crusing or deceling...it sometimes goes to 17 of afr...which it never does when it runs normally without this issue..

[BadAssPerformance]

Might be a bad gound somewhere... at least for the AF guage

[turbovanman²]

Check fuel pressure while driving.

What's your fuel system setup?

Also what JT suggested.

[89ShelbyGuy]

Walbro 255 - Accufab Adjustable Regulator - TU Custom fuel rail - +20 injectors

[cordes]

How much timing are you running? It is possible to run enough timing to have knock regardless of how rich you are. That's pretty much the definition of octane limited.

[89ShelbyGuy]

Timing was set to stock, but not checked recently.

My whole thing is....the problem hasn't always been there...it acts up at times...it seems when i start playing with crap in the engine bay, it goes away...so..my next step is checking and cleaning all my grounds....check my wideband ground...

[cordes]

Timing was set to stock, but not checked recently.

My whole thing is....the problem hasn't always been there...it acts up at times...it seems when i start playing with crap in the engine bay, it goes away...so..my next step is checking and cleaning all my grounds....check my wideband ground...

My WB was never happy unless I grounded it to the battery.

[89ShelbyGuy]

My WB was never happy unless I grounded it to the battery.

Yea, but did it give you knock readings like i am explaining?

[cordes]

Yea, but did it give you knock readings like i am explaining?

No just the inconsistency. you're probably getting knock somehow. Can you monitor your knock voltage at all?

[89ShelbyGuy]

If i were to data log it...which maps would be helpful to the advance gurus to figure this out? I'll set up my mp scan with my ftdi adapter.

[RoadWarrior222]

Somebody somewhere, should set us up a jet spray carwash with contact cleaner instead of water, then when we get these old car problems that are 90% likely to be a bad contact somewhere, we could just run the whole damn thing through

[cordes]

If i were to data log it...which maps would be helpful to the advance gurus to figure this out? I'll set up my mp scan with my ftdi adapter.

If you can look at the cal in MP Tune you can see the total timing and take a screen shot. That would be super helpful.

otherwise if you could data log the knock volts vs. rpm with no load on the motor and then again while driving around it would help.

[wallace]

What condition is the injection harness in? I've got to rewire the one on my wagon it has cracks in the insulation and if I work on the car and disturb it I end up having to move it around to get the car to run right.