Need help… no boost

[Slow998]

Oh.. you are right.. hmm.. The TPS thing seems to be real at least that there is a correlation between what the sled thinks is happening and what is happening to boost. Can you switch the scale on the left so it is boost instead of mph?

You’re right, earthling. Anytime the throttle dips, the boost spikes.

 

[74Nitro]

You’re right, earthling. Anytime the throttle dips, the boost spikes.

I think that may be normal. You just closed the throttle valves and the system needs a small amount of time to react.

 

[earthling]

The boost spikes I guess are normal but it means that the ECU really thinks that the throttle is not solid at 100%. Changing the scale just makes it more visible. No idea however why the map without the throttle dips has the boost running lower... unless. If you go back to the map that has the high boost, I wonder if the throttle dropping out is causing boost spikes giving you a false boost reading?? Changing the scale on that log to PSI on the left will magnify what is happening to boost pressure throughout the run.

 

[74Nitro]

150psi across all 3 cylinders. Cam timing is lined up.

Have you done a leakdown test on each cylinder?

 

[Slow998]

Have you done a leakdown test on each cylinder?

I have not, yet. I plan to bring the shops leak down tester home so I can do that.

 

[Slow998]

Cylinder 1

 

[Slow998]

Cylinders 2 and 3 are less than 10% leakage

 

[KnappAttack]

What makes you think there is a problem? Are you running a different wastegate than stock or shimmed? Typical boost on header tunes are not typically as high as 19 lbs. More like high 17 to 18 lbs as the wastegate can't stay shut with exhaust pressure.

You may notice more boost with less RPM I'm betting, more RPM less boost? A new belt or belt change could change the RPM and raise the RPM and drop the boost that little bit? These sleds never seem to do the same thing from day to day, one day its on point and the next and you are chasing something thats off a bit. I don't think the wee bit lower boost is related to blowing a belt unless you spit a shim, and you'd know it if you did.

 

[Slow998]

What makes you think there is a problem? Are you running a different wastegate than stock or shimmed? Typical boost on header tunes are not typically as high as 19 lbs. More like high 17 to 18 lbs as the wastegate can't stay shut with exhaust pressure.

You may notice more boost with less RPM I'm betting, more RPM less boost? A new belt or belt change could change the RPM and raise the RPM and drop the boost that little bit? These sleds never seem to do the same thing from day to day, one day its on point and the next and you are chasing something thats off a bit. I don't think the wee bit lower boost is related to blowing a belt unless you spit a shim, and you'd know it if you did.

My primary cause for concern is the 17.9 pounds of boost compared to the usual 19.4 that I typically see. Coincidentally, when I hook my boost leak tester up, that’s exactly where I can hear air start flowing the the exhaust, right at 18 pounds. Last time I tested this sled, I would get over 20 pounds before it started to leak anywhere

 

[74Nitro]

Cylinders 2 and 3 are less than 10% leakage

Leaking where?

 

[Slow998]

Leaking where?

I can’t upload the photos for those 2 cylinders but they’re tighter than the picture I uploaded for cylinder 1, which is showing 11% leakage.

 

[Turboflash]

150psi across all 3 cylinders. Cam timing is lined up.

Stock spec for 998 compression is 176 psi. If yours is really 150, either your gage is wrong or there is something wrong w engine.

 

[Fleecer]

Stock spec for 998 compression is 176 psi. If yours is really 150, either your gage is wrong or there is something wrong w engine.

Being that all 3 read 150psi, I would lean towards the gage reading low? It would be tough to have all 3 pistons hurt equally?

 

[KnappAttack]

Being that all 3 read 150psi, I would lean towards the gage reading low? It would be tough to have all 3 pistons hurt equally?

Right. Pistons don’t get hurt from blowing a belt. The valves sure can though but typically it would spit a shim on the exhaust cam side if the valves hit.

No two gauges will read the same. I had a snap on gauge that always read low like that, another gauge that read high. They will be all over the board. Leak down is fine so I’d be looking for a leak like he’s doing, but like I said the boost is right where it should be using stock wastegate actuator. 19 plus lbs boost is not normal for that header setup and typically can’t/never happens because of exhaust pressure blowing gate open. Takes more than normal stock actuator spring pressure to get over 19 lbs. it’s possible, but the majority of machines never see that high without work to get it there.

 

[sideshowBob]

Maybe you are getting an exhaust leak like a cracked header?