GM ECU 1227730/47: basic questions

[Shannen Durphey]

John Zarli wrote:

> Shannen, have you tried a NEWER manifold on an older bolt pattern head?

Well, not until you asked.  I just went to the shop and set some 283 heads on a 400 block
and put a 93 Caprice TBI intake on top.  This is not a problem.  I was using 2 1/4" long
bolts which were lying on the floor and there was plenty of room (lengthwise) to start
them.  The center bolt holes are at 72 deg instead of 90 (in relation to the manifold
mating surface) so your washers need to have an 18 deg. angle.  I used a rotary burr to
elongate the holes, but since the manifold's aluminum, a guy could use a drill bit.  I know
that I looked for machined washers at one time, and they're available.  I can't remember
where.  I'd start with Edelbrock and Summit.

> Also, can you clarify the your statement about watching the ECM pulse
> extra fuel?  How did the engine misbehave?...Also note that 215^ is up
> yet another notch from from the 208 of the ZZ3 cam, which by all catalog
> indications is pushing the limit for stock FI.

  At the time I couldn't find any info on max. duration for TBI apps.  I called Crane Cams,
BS'ed with the tech a while, and he said no more than 215 deg @.050.  Then I called a parts
warehouse and ordered an engine kit with special cam.  Here are cam specs:

            lift            dur(adv)            dur(.050)            overlap
lobe centerline
int        .4425            288                214                        64
107
exh       .4425            288
214                                            117

When I fired this up, it wanted to idle @ 600rpm(warm, closed loop).  At that speed, the
cam caused little reversion pulses in the manifold, which the ecm interprets as rapid
increase in load, and quickly richens the mixture with extra pulses.  Generally the engine
runs ok, but there are some bugs around 140 deg F in closed loop, like stalling at a stop
sign after rapid decel.  Also, in cold weather in open loop it really loads up.  (I've
since learned this problem is inherent to crossfire.)
If I turn up the idle speed to 850 or so, this all goes away, and when I finish the
restoration, I'm going to modify the prom to increase idle speed.

If you end up converting your vehicle, let me know how it turns out.  We had a carb'ed ZZ3
in our shop and it sounded like it had a pretty rough idle.  I've picked up more info about
the cam profiles if you're interested.

Shannen