I have 1997 AEB B5 that I thought was only pushing 4lbs of boost. I was directed (by this amazing forum) to a few possible problems:

1. Limp Mode - nope. The 1997 doeant have limp mode. I have 1 code on vagcom bit is for the g63 (I think. Its the one on the upper back of the block that's bad) coolant sensor. I know this will affect trims but this shouldn't limit boost that much.

2. N75 valve - I took the wastegate line off and the boost gauge read -10 inhg which would lead most to think there is a huge vac/boost leak. When I test drove it, I hit the fuel limiter at 6 psi. So I know that the engine is getting lots of boost pressure. So it shouldn't be the n75 right?

3. Huge boost leak - I originally thought that this was definetly the problem as I didn't have a dv line hooked up when I bought the car. I also thought it was a leak because it runs really rich. But I've since been told that this is also probably caused by the coolant sensor always reading too cold.

Because the boost gauge only read 6psi when I hit the fuel limiter, this is what I think. My boost gauge is t'd into the DV line. So either the DV is leaking a lot of boost, my boost gauge isn't reading correctly, or the tubing I used is garbage. The tubing is just some generic PVC tuning that I got at the local auto parts store and its a couple of millimeters too small, I had to stretch it to get it on the fittings.

Should I be getting boost readings from the manifold pressure or directly from the turbo? I'm going to isolate the DV as the issue by connecting the boost gauge directly to the IM and see what it reads.

Thoughts?

 

I have a 97 1.8t and yes they do have limp mode. Check vacuum lines for broken/cracked lines and boost leaks. Mine went into limp mode when the MAF failed the first time...only made about 5-6lbs of boost. As for the coolant sensor, I just replaced mine. Since you have access to a vagcom run a gauge test (do a sweep) this will verify the gauge works/doesn't. Check to see if you have the green top coolant sensor...the black top ones are prone to fail. If it's not either of these you most likely have a bad thermostat (just did that tonight). That's where I would start.

 

So a faulty MAF won't cause any codes? The only code I have is for the g62 sensor. Will a faulty g62 cause low boost?

I bypassed the DV so the boost gauge is hooked up right to the intake manifold and I have proper vac now (-18 inhg or lower). The DV is still connected to the TIP and the IC tubing. Just boost line isn't hooked up. Will this cause a loss of boost? I was able to freely blow through the boost line on the DV so I'm thinking this might be a boost leak.

I have a black top coolant sensor. Will a faulty g62 cause limited boost?

I had the front clip off about a month ago doing the timing belt so it would suck if I had to do it all over again to change the thermostat. But my engine ran at normal temperatures before the g62 started throwing a code.

When I disconnect the wastegate from the n75, I get full boost, so I don't think I have a boost leak. So either the engine is limiting boost or I have a faulty n75.

 

I thought stock boost was around 7 PSI...? No? Don't remember.

 

I guess you're right. I thought it was around 10-12 psi but that's for the awm.

I see spikes of 7lbs and then it settles at 5 or 6 so I might still have a small leak. Shouldn't it spike higher than 7lbs?

 

When my maf went out I didn't get any codes. 7psi is normal bone stock. I'd hook up the dv so you don't get any surging...not that it matters at 7 psi. But it should smooth out the general running of the motor. Change out the sensor...I'm assuming the temp gauge on the dash is always at cold? Coolant sensor is really easy 5-10 min tops...pull the connector and then the c clip holding in the sensor into the casing. As for the thermostat that's pretty easy as well...you don't have to remove the front. Remove the support bracket (jack up the car and it's on the drivers side) and 2 10mm bolts on the housing. It helps if you have a 90 degree 10mm wrench for the bolt closest to the front of the car. It's located towards the front of the motor. You will loose about a gallon of coolant so have a catch bucket handy. Replace with (G12, G13, G30) not 100% on that but it's a g variant (not green coolant)(make sure the engine is cold, you don't want to get scalded). But a temp sensor and thermostat will only cost you about $30.00. Get the gaskets for both as well...coolant sensor usually comes with one but my thermostat didn't.

Stock hp for an AEB is 150hp 150ft/lbs
Chip that thing...cheapest way to get 200hp and 210ft/lbs ($200-$500) depending on brand
Mine's stage 1 and boosts about 15psi

 

Im ordering the sensor from ecs soon. The dash does always read cold. I didn't have a problem with the thermostat in the summer but I'll see how it is after I do the sensor.

Its still hard to tell if I have a bad n75 or something else wrong. I'm only boosting 4-5psi with spikes of 6 and that's also what the wastegate does stock (as far as I'm aware).


Ill be doing a giactune/bigger turbo/fmic/all of the fun stuff in the spring. I just want my boost back for the winter.

 

I'm guessing worn out thermostat then...mine took a while to warm up in the summer before I replaced it. The gauge would read cold for about 5 miles and then get to about the middle or less on warm days. Most likely the thermostat is stuck open or shot so coolant is flowing through the entire system and not being allowed to reach operating temp which stock is 190-192 degrees. My s10's thermostat went out at the beginning of winter...It helps when there are numbers on the gauge...I was only getting around 130 degrees but that did throw a code which helps.

 

99.99% a bad thermostat. You can get a new one for about $10. I replaced mine... twice. The 2nd time wasn't necessary though as it was my coolant temp sensor, so I got soaked with coolant for no reason the 2nd time.

 

Changing the thermostat tonight as well as the sensor just cause its a black top as well as an oil change. Thanks for the very helpful insight.