Swapping 424 with 531 VR Statesman

[Icey83]

Hi All,

Thanks for all the valuable information and tips from this site. It’s been a great help.

I have just completed the install and patch over of a VT 5.0 harness, dizzy and sundries into a VR Statesman including a MR Module BCM emulator.

So far so good, every thing is working and car fires up with still a bit of work to do to finish off 100%.

Questions I have for someone that might know:

1. In some documents I read the 531 should have a Trip wire like the 424. However the pin on the VT loom is not filled (F7 I recall, but don’t quote me). If I install a pin, will that pwm signal be there for the VR Trip Computer?

2. The engine is a non roller engine and I have read the knock sensor might struggle with slightly more noise from the valve train. Has anyone seen this actually?

3. If I tie the ALDL data line to the VR BCm and module what will this do? I am hoping by some miracle It might solve the BCM wait issue it has engaging starter motor.

4. Can you mod the Speedo ratio on the 531? Eventually this car will be getting 3.7’s.

Finally, this car has a slighty warm motor ie: flat tops, 286 cam (the usual goto mods for a 304). What’s the chances of it starting and holding idle once base timed? The LSA is 111deg instead of 110 for the 286. Should I go 10deg BAse time or aim for 12?

Once basically running the next step is to begin playing with the tune. Cheeky question… does anyone one have something close to suit (automatic). I will start another thread when I get there regarding tune anyway.

Thanks in advance.

[Knackersjewels]

It's probably too late at this point, I'm a bit late, but here's my 2c:

2. Get some knock ears and see if it detects actual knock, and adjust the attack rate and ignore time to suit. It won't be perfect, but if it's a noisy engine, you may be able to get it close. If not, tune it safe.

3. You'll have problems, as VT PCM and VR BCM are both bus masters, so will be sending signals across each other.

4. It's not listed in the enhanced mod, but it could be done. It won't affect the VR dash though, it'll need a speedo adjuster

5. It should run somewhat on the factory tune. LSA has nothing to do with the base timing. Set it to 10 degrees, as it should be, and use the computer to adjust. You'll need to take a little bit of timing out under load because of the higher comp, so advancing the base timing just adds 2 degrees everywhere, which will make it more likely to ping. Don't try and cheat it, it'll hurt you later.

[Icey83]

Thanks mate, answered nearly all my questions.

Wasn’t too late, this car is literally a side project for a mate. I tinker in the evening when I have a moment or on Saturday.

Think it’s time to get the NVRAM on order.

[Icey83]

A question for the brains trust on this site. I can get this car to fire up with the O2 sensors unpluged. This indicates to me (based on what i read) that the PCM must default to batch firing the injectors. The problem i seem to have is when the O2 sensors are plugged in. It wont start.

I played with dizzy plug locations, setup a noid light on cyl 1 injector and everything seems ok. However what i am suspicious about and can not for the life of me find info on is if the pulse timing is right. The dizzy is a repro and i suppose i should trust its manufactured the same as an OEM item but i dont… i have followed all of the GM manuals and checked 3-4times but still no luck.

Bench testing the Dizzy, the home signals falling edge commences on or around plug 6 and rises just before 1. The plug points mentioned anre according to the GM manuals and home edges from tests. Can anyone confirm this is right so I can chase a different issue. Cheers,

[Icey83]

Slight reply to myself here, but still wouldn’t mind knowing the home reference to plug 1 on a dizzy.

For anyone else in the future…
Never underestimate how old fuel can kill spark plugs. 7 out of 8 after firing up the night before and turning the key the next morning.