Massive Knock with E85

[TheHydro]

Hey guys. I need some guidance with my current issue. My set up is a gen 3 whipple with 3.375 pulley, fore twin pump fuel system, mak cat deletes on E85. I have a custom tune from a well known local tuner and when I was running the same set up with a 3.625 pulley I had no issues. I dropped to the 3.375 pulley and went to get a retune and my car was knocking on the dyno. I took my car home and made sure both fuel pumps were working and fuel pressure is right where it should be. Did a couple pulls on the freeway. First pull made around +5 degrees of knock. The next couple pulls had no positive knock and hauled ass. The last couple pulls I made got up to +10 knock so I didn’t do any more pulls since then. Car runs great except for the massive knock at WOT. I know fuel pressure is good and fuel quality is good, where should I start my search to fix the problem?

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[SolarFlare]

How do you know fuel pressure is good when making street pulls?? Was tuner or you watching FP gauge when on the dyno?

 

[SolarFlare]

With something as simple as a pulley change I’d go back to what you previously had and test it for a couple days. If there are no issues, then I’d say for whatever reason (lack of line size, weak pump or just too small of a pump, etc) the fuel system is not keeping Up with higher fuel demands vs lower demands.

 

[Roh92cp]

Make sure your hobbs switch wires are tight in the controller, had a friend this happen to and the hobbs switch was going on and off and he was mostly on one pump. In fact make sure all connections are good. Also I would be logging the A/F and see wha that is doing while your getting knock.

 

[TheHydro]

I have a fuel pressure sensor connected to my zeitronix zt2 that I monitor on my ngauge. My fuel pressure sensor is spot on with my regulator gauge. I was thinking my next step would be to go back to my original pulley and see what happens.

 

[TheHydro]

Make sure your hobbs switch wires are tight in the controller, had a friend this happen to and the hobbs switch was going on and off and he was mostly on one pump. In fact make sure all connections are good. Also I would be logging the A/F and see wha that is doing while your getting knock.

My tuner was originally thinking maybe there was an issue with the Hobbs switch but I ruled that out by jumping the Hobbs switch and having the pump run full time and still got a lot of knock.

 

[bluebeastsrt]

Are you getting the knock. Thru the entire pull? Or do your logs look like a stair case? My tuners just told me to never use a Hobbs switch. More trouble than there worth. Anyway. If both pumps are pumping. And your sure there is no short to a pump. The regulator would be the next thing to check. Dialing these fuel systems in. An be a pain.

 

[TheHydro]

Are you getting the knock. Thru the entire pull? Or do your logs look like a stair case? My tuners just told me to never use a Hobbs switch. More trouble than there worth. Anyway. If both pumps are pumping. And your sure there is no short to a pump. The regulator would be the next thing to check. Dialing these fuel systems in. An be a pain.

I have not reviewed a data log as I’m not familiar with reading them. I have just been reading the real time data from the ngauge. My tuner also said he recommends not using a Hobbs switch but I still have that same problem with the pump wired directly. I had 70lbs of fuel pressure when I got +10 knock so that’s why I’m not sure where to look. The only thing I can think is maybe some type of clog at a fuel injector but my ID1050X injectors only have a couple thousand miles on them and I run Lucas fuel injector cleaner and ethanol stabilizer in every tank. I also don’t let my car sit for more than a week at a time without driving it.

 

[bluebeastsrt]

A log will go a long way. To figuring out your issue. I don’t own an Nguage. But you can log directly from that using HP tuners or live link. Software. A stair case looking log. Most likely indicates false knock. I just dealt with this issue recently. Turned out. I had a header that not only was cracked at the collector. But was also rubbing. The vibration drives the knock sensor crazy. False knock is pretty common. A clogged injector would most likely throw a lean cel on which ever bank the injector is located. A quick and dirty way to check. Is to start the car and feel the exhaust manifold. If you have a clog. One cylinder will be colder than the others. Have someone rev the engine. And shoot all the exhaust ports with a temp gun. That’ll also indicate a clog. If one cylinder is colder than the others. It’s possible the injector is bad or clogged. But I’d bet on other issues first. I’d double check that both pumps are working. You’ll have good fuel pressure on one pump. And go lean at wot if the second pump isn’t working. Ditch the Hobbs switch. Youve direct wire both pumps. So it’ll be easy to check and see if your getting power to them.

 

[TheHydro]

Today I switched back to my 3.625 pulley, belt and tune I was using before to try and rule some things out. I made several pulls and about half of them had negative knock or zero knock and the other half the pulls had positive knock up to 4. Fuel pressure was spot on throughout every pull. I’m confused how half the time I don’t have knock and half the time I do. At this point I don’t believe it to be false knock as going back to the bigger pulley brought the positive knock down from 10 to 4. Anyone have any ideas why I am seeing knock intermittently and not on every pull?

 

[silver50]

Can the intermittent knock be from the heat? You are in Vegas, what's your IAT?

 

[TheHydro]

Can the intermittent knock be from the heat? You are in Vegas, what's your IAT?

I considered this but all my logs had 97-99 IAT and some had knock and some didn’t. I ruled out heat soak because the first couple pulls on different days had knock and then a pull or two later no knock.

 

[Roh92cp]

I feel for you guys trying to find this phantom knock that some get. I on the other hand lucked out I guess and early ever see any knock ever with PBD 22 degree on 93 plus 10 oz boostane and 7 gph meth. It sometimes is scary to see nothing, makes me wonder if the knockers are even there.

 

[Tommy V]

I know this is going to sound crazy but knock sensors have to learn also.I have noticed especially when locking the car in sport mode and doing pulls starting from 3k and just flooring it,i would get knock also.Especially when on a new loaded tune.Also if you are getting any wheel spin it will cause knock.You have to look at a data log to really tell whats going on.Everytime i do a log and see wheel spin in the log,i see knock and timing pulled.Also if your really getting 10 degrees knock your plugs will show it.

 

[TheHydro]

I know this is going to sound crazy but knock sensors have to learn also.I have noticed especially when locking the car in sport mode and doing pulls starting from 3k and just flooring it,i would get knock also.Especially when on a new loaded tune.Also if you are getting any wheel spin it will cause knock.You have to look at a data log to really tell whats going on.Everytime i do a log and see wheel spin in the log,i see knock and timing pulled.Also if your really getting 10 degrees knock your plugs will show it.

Thanks for the input. I will check my plugs and see how they look.

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