1994 Nissan Sentra SE-R going VEMS, then turbo.

[BenFenner]

The EGT was giving what looked like good readings, just maybe uncalibrated (never calibrated it).

I drove it around all day yesterday and tuned a bunch in the evening and it didn't skip a beat (EGT disconnected).

You want me to see the voltage between the engine block and what exactly? The metal probe, the braided shielding, one of the thermo coupler wires? While the EGT is connected to the ECU or disconnected?

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The EGT probe and the block - I'm thinking perhaps the engine is finding a ground path down through the egt probe, the ECU might not like that...

[BenFenner]

The EGT probe and the block - I'm thinking perhaps the engine is finding a ground path down through the egt probe, the ECU might not like that...

So you want me to take the EGT probe out of the exhaust manifold and check the voltage between the probe and the block while the probe is plugged into the ECU and the engine running? Maybe give it some revs, etc?
Gotcha.


Not sure if/when I'll get around to that. I've decided that losing the EGT measurements isn't a huge deal, and I have racing to do. I'm pretty sure you're right about the grounding thing. I'll let you know if I get the chance to check that out. For now I'm just excited to have the car working properly and boosted. =D

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It will be great to see what sort of power you get with the boost.

If there is a ground path via the EGT probe you could do a load worse than sorting it properly and making up a grounding kit for your car - it will certainly help you clean up any noise issues, and the EGT would be more than a little helpful for wringing out every last drop of power from your engine.

[BenFenner]

When you say grounding kit, you mean a typical engine grounding kit? Because I have a home-made one. The engine grounds were missing on the car and the starter wouldn't turn because of it. Swapped starters before I realized what was going on. Ended up running a beefy ground where the stocker had failed, then added another to the rear of the engine. There's one on the exhaust from the factory by the catalytic converter that was sheared when I bought the car and never replaced. Maybe I should do that, but from my view I should have at least decent grounding... =/

I'm also excited to see what kind of numbers I get out of this thing. I have high hopes for it. Not numbers-wise but efficiency. I won't ever make any real power because the transmission is a weak link I don't plan on grenading any time soon. The T28 (Pulsar GTi-R) turbo is known good to 300-320 WHP or so at around 18 psi (224 kPa) on the ragged edge. I'm running an 8 psi (155 kPa) wastegate and seem to get boost creep up to 11 psi (175 kPa). Stupid free flowing downpipe is making the turbine look much more appealing than the wastegate.

Most people make around 215 WHP or so with 11 psi. I know I'm making over 240 to the wheels, maybe a lot more. We'll see when I hit the dyno. =]

Then comes the progressive boost control. 

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When you say grounding kit, you mean a typical engine grounding kit? Because I have a home-made one. The engine grounds were missing on the car and the starter wouldn't turn because of it. Swapped starters before I realized what was going on. Ended up running a beefy ground where the stocker had failed, then added another to the rear of the engine. There's one on the exhaust from the factory by the catalytic converter that was sheared when I bought the car and never replaced. Maybe I should do that, but from my view I should have at least decent grounding... =/

The grounding kits all ground to a single point on the chassis, it would be good to ground the block, head, starter and alternator all to a single point, and if that single point is the same one that the ECU uses - theres a cluster in the middle of the firewall on the S14 I don't know if theres something similar on your chassis.

[BenFenner]

Okay, thanks for the help. I will add it to the list of minor details I'd like to iron out.

FYI my factory ECU grounds are at two bolts on the top of my intake manifold (as far as I know). Sorry for bad pic.

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Where do those grounding points connect to the chassis?

[BenFenner]

That is a very good question. I have no idea. I will check as I'm curious too, just never took the time to follow them. Also, will check to make sure they actually are the ECU grounds. They might go through a grommet in the firewall directly to the ECU? *shrug*