MR2 Boost when hot

[matt dunn]

just a guess but I would have though it would be knock sensor related, as if it detects a more than normal amount of knock, and it drops a bit of advance and it's still there, it may drop the boost,
and knock would be worse when th IC is hot????

[MR2SIK]

If it was knock then the check engine light should come on?

[sergei]

If it was knock then the check engine light should come on?

Not really. If it was large enough for ECU to register as faulty sensor then CEL would come on.

[fivebob]

Without accurate intake temperature readings it's a bit difficult to determine if there would be excessive knock caused by a heatsoaked I/C. At such a low boost level (8-9psi) the CT26 is running near peak efficiency, and, assuming that there is not too much time spent at low speed, IME the I/C should be able to cope without too much heat soak.

Also the situation of excessive knock causing the ECU to reduce boost should result in the boost fluctuating as the knock level reduce. I seriously doubt that knock would continue with if the ECU retarded the ignition (about 15°) and reduced boost. So therefore boost should return to normal.

[fivebob]

Another possibility is an exhaust leak. Cast manifolds can warp and unseal but only when excessively hot. No you won't nessecarily hear it either.

While prior to Chassis # 59266 the manifolds had a warping issue, it's not really possible for the manifold to leak enough to reduce to boost to the level that an open wastegate would.

Given that the wastegate would remain shut, as there would be insufficient boost to open it, then the leak in the manifold would have to be huge and IMHO you would hear it loud and clear. Generally speaking when the manifold warping issue manifests itself on those engines the first thing you notice is the sound and AFAIK there is no discernible loss of boost, certainly not to the extent described here.

[Akane]

Akane do you run an aftermarket boost controller AND the vsv plumbed in together?

Yes I was. It's okay on the street but once I hit meremere on a hot day it goes haywire.