Heavy miss/cut out as I cross over from vacuum to boost

Jaker · Post by **Jaker** » Sat May 08, 2010 9:53 pm

I cannot get my engine to accept any boost. As soon as I transit past zero vacuum, it bucks and spits and will not work. I fear damaging my freshly rebuilt motor, so I always let off when this happens.

The only thing that I can think of is that I messed with the settings under the options tab - settings - units:

I set the vacuum unit to " (inches of vacuum like the readings on my boost gauge), vacuum unit base to atmospheric and the pressure units to PSI and the pressure unit base to atmospheric.

Here is the tune (using a Motorola 2.5bar sensor) and a datalog:

Jaker · Post by **Jaker** » Sun May 09, 2010 11:12 pm

I've played with it a bit, and now know that the settings in the Options menu are not the cause. Here's the most current version and still no dice.

Post by **Spunkster** » Mon May 10, 2010 9:45 am

Why are your intake temps so high?

Jaker · Post by **Jaker** » Mon May 10, 2010 11:59 am

Non-intercooled M62 blower. I think because it's not getting to open up much it's getting hot.

Post by **Spunkster** » Mon May 10, 2010 1:42 pm

Do you have a map relocator so the map sensor is actually seeing boost?

Jaker · Post by **Jaker** » Mon May 10, 2010 3:07 pm

Yes. MAP sensor is located inside the ECU (Motorola 2.5bar mounted on a small plate, hard wired into the ECU), and vacuum line goes to the intake manifold post blower (between the blower and the head). Datalogs are showing boost occasionally, but only a couple PSI, and that's usually when I let off.

This is the way I ran the car back in 2006 (last time the setup was running) and it worked perfectly.

Jaker · Post by **Jaker** » Mon May 17, 2010 6:59 pm

After much troubleshooting and part swapping my trouble ended up being spark plug wires. I didn't try that right off the bat because the wires (Magnecor 8.5mm) only had about 20 hours of driving on them, tops!

locash · Post by **locash** » Mon May 17, 2010 10:09 pm

We only use OEM wires, even on high hp cars..

scttydb411 · Post by **scttydb411** » Thu May 20, 2010 11:55 am

oem or ngk wires. msd as a last choice.
been there done that...spent hours troubleshooting one of my oldest customer's car and didn't check the wires since they were ngk and this is 5th high hp car i've tuned for him. it turned out he was using the same wires from the first car I tuned for him 5+ years ago.

don't forget to rule out the simple and normal checklist items.