[urq] What cause overboost ?

[Louis-Alain Richard]

On Eric's 1985, I tried 3 ECUs:

- the one that came with the car. Cut-out at near 4000 rpm. When I opened
the ECU, one of the chips (OEM stock is :HITACHI R21021 2332(A) 421 MAC02V1)
looked it had been replaced with an unmarked chip except for a paper tag
(AXJ103 <04>). So it might be chipped. No one knows for sure.

- Brady's chipped ECU. The same chip (HITACHI R21021) is obviously replaced
with a (LD2732A25, paper tag L24E Mo2) chip which is mounted on longer
"legs". With this one in the car, we were able to push the engine over the
4000 rpm for a short period then the cut-out came back. 

- My own 1983 not-chipped ECU. With this one, cut-out is at 3000 rpm under
load, but the engine can go over 3000 rpm if we feather the throttle.


Now, this leads me to believe an overboost situation that cause any ECU to
stop the fun at different RPMs. But, if there is no obvious leaks in any
hose, as I found last night, what can cause overboost ? 

If the timing is way off, could it be enough to cause overboost ?

By the way, at idle, the engine is VERY smooth and quiet. This made me
wonder if the head was replaced (hence my question about the vacuum pump
boss) with an hydraulic one. 

Is there a way to identify a correct WX head from another hydraulic head
easily ? Without removing the valve cover, obviously...

Last question: could it be a failing fuel pump relay, or a failing
distributor ? It does feel like an ignition cut-out.

Thanks in advance,

Louis-Alain