Knock under boost

[Favian Cuevas]

Well i did a coversion on my 85 a while back an since i did tje swap motor the car runs good but i keep geting knock under boost ived done the following
Injectors
Plugs gaped at 35
Wires
Coil
Control module
Ive tried 3 diff chips
2 set of injectors
Adj regulator
An i only get knock under high boost

 

[~JM~]

What is: "High Boost"?

What fuel are you burning?

 

[Favian Cuevas]

What is: "High Boost"?

What fuel are you burning?

91

 

[psycho6cyl]

As stated above what's high boost? On 91 you should be doing17lbs max. I'd turn down boost. If anything you don't have enough octane

 

[Favian Cuevas]

Im running 14psi i xhecked with a gauge an powerlogger

 

[fastblackracing]

Do you have a fuel pressure gauge that you can watch while you road test the car?

You need to verify that you have a base fuel pressure of 43# vacuum line of the regulator
and the pressure must rise 1 to 1 with the boost so you should have 57# at full throttle.

I have seen on three cars where the fuel pressure would not keep up....
one car a section of the steel line had been replaced with rubber hose and
the rubber hose was pinched under another line......
one car the steel section of the boost reference line from the throttle body was
completely rusted shut inside and this was a low mileage car....
one car the fuel pump was simply worn out....

I have also seen where the boost gauge line was leaking and the turbo was
making much more boost than the gauge showed....

You might want to list any mods that are done to the car and also
when does the knock happen? as soon as boost comes on....or on a gear change
and how much knock is it showing?

I am assuming you are stock or close to it with the stock injectors....
And a stockish engine with a knock problem is usually fuel pressure or boost pressure related.
You want to make sure your pressures really are what you think they are going down the road.

Also if the car still has the cat converter on it is another potential suspect.

 

[Favian Cuevas]

Im running 14psi i xhecked with a gauge an powerlogger

Do you have a fuel pressure gauge that you can watch while you road test the car?

You need to verify that you have a base fuel pressure of 43# vacuum line of the regulator
and the pressure must rise 1 to 1 with the boost so you should have 57# at full throttle.

I have seen on three cars where the fuel pressure would not keep up....
one car a section of the steel line had been replaced with rubber hose and
the rubber hose was pinched under another line......
one car the steel section of the boost reference line from the throttle body was
completely rusted shut inside and this was a low mileage car....
one car the fuel pump was simply worn out....

I have also seen where the boost gauge line was leaking and the turbo was
making much more boost than the gauge showed....

You might want to list any mods that are done to the car and also
when does the knock happen? as soon as boost comes on....or on a gear change
and how much knock is it showing?

I am assuming you are stock or close to it with the stock injectors....
And a stockish engine with a knock problem is usually fuel pressure or boost pressure related.
You want to make sure your pressures really are what you think they are going down the road.

Also if the car still has the cat converter on it is another potential suspect.

I dont have a outside mounted fuel gauge just the one on the rail its also set at
42 of vacuum
Knock ive seen it around 14 all the way to 16 not good ..
New walbro 340 pump with hot wire
Its running straight pipe to a pitbull muffler
. Ama have to check boost again when i get home..
I did forget to mention as well the engine is pared up to a 85 t type transmission and torque converter .. an also in first gear i have no power whats so ever not until boost kicks in ...im not sure if that has something to do with it ..

 

[Sinister CO]

What does your O2 voltage look like under boost?

 

[TTA976]

Use the fuel you have but 91 sucks. Id only use Eric's or Bob's chip these days. You need a WB to check the A/F @ wot...I'd stay around the 11:5 -11:7 and that boost level. I'd check the valve train too. Does the knock hit like 1-2* then go away or does it climb (4, 6,10 etc)...

 

[Favian Cuevas]

I will load some files when i get home ... but if i remember it normally stays at hi 700 an mids 800 if i remember correcly..
At times it also drops dead when its around 13.9 pounds of boost with 7.9 of knock

 

[Wahoo]

Whats your TPS sensor read at wot?

Whats your scan master numbers.

I would stop running that much boost until you can figure out the problem

 

[Sinister CO]

I will load some files when i get home ... but if i remember it normally stays at hi 700 an mids 800 if i remember correcly..
At times it also drops dead when its around 13.9 pounds of boost with 7.9 of knock

It should stay pretty steady the whole time. If you're getting big dips it could be your fuel pump.
I always like to start with the simple things first so I'd put a new fuel filter on it if you haven't done that lately.
Assuming that doesn't help, you'll probably want to get a fuel pressure tester to check it under boost. I think you can borrow them from some parts stores but I don't know if you'll find one with a long enough hose to get it to your windshield. You might have to buy a longer hose.

 

[Favian Cuevas]

Hey guys i havent had time to run the car an logg some runs due to work an also the heat in arizona but as soon as i do i will post them on here ...
Something else that i forgot to mention from dead stop if i go to WOT the car will fall in his face starts to sputter an sounds like it wants to die untill the boost builds up it starts to take off but till then it wont even go ...

 

[Favian Cuevas]

Hey guys i havent had time to run the car an logg some runs due to work an also the heat in arizona but as soon as i do i will post them on here ...
Something else that i forgot to mention from dead stop if i go to WOT the car will fall in his face starts to sputter an sounds like it wants to die untill the boost builds up it starts to take off but till then it wont even go ...

Use the fuel you have but 91 sucks. Id only use Eric's or Bob's chip these days. You need a WB to check the A/F @ wot...I'd stay around the 11:5 -11:7 and that boost level. I'd check the valve train too. Does the knock hit like 1-2* then go away or does it climb (4, 6,10 etc)...

Yea the knock does climb as soon as i get on it ...

 

[TexasT]

Turn the boost down and get off the throttle at any Kr. You are gonna get a lesson in hg replacement.
Stock maf? These are getting old and the replacement units don't have a very good track record. Is it showing the full 255 when you go wot?

Fuel pressure and volume is crucial for keeping the heads on the sealed up. As above you need a fuel pressure gauge on there so you can see the pressure ruse with boost.

Stock turbo? Stock
Intercooler?
What brand/type plugs are you running?
Resistance on the coil?
Let us know how you do.