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View Full Version : SR20DET - boost problems


triumph_013
10-11-2011, 05:59 PM
Ok, I have this same thread posted on another forum, but only one guy is trying to help and it's a slow process. Hopefully I'll get more attention over here.

1990 fastback
Red top SR20DET
Factory turbo
3" turbo back exhaust
Greddy FMIC
Greddy BOV
Greddy PRofecB Spec-II

This is my first turbo car. I don't know much about them, but I do try to do as much research on my own as I can. I can't find much on my issue, so I'm hoping someone else can help me. I didn't build this car, I acquired it with the swap already done. The first night I got it the boost controller was set to 13psi and did every bit of it. Spooled up quick and pulled hard to redline. A couple days after I got it, it didn't want to go past 10-11psi. I didn't change anything to the car, I just drove it. I also drove it easy, I wasn't hard on it at all except the night I test drove it. The boost was inconsistent, it wasn't going to the same psi every pull (using the peak boost feature on the boost controller). It also felt like it was pulling hard, then slacking off after about 5k rpms. I tried to play with the controller to see if I could change anything, and nothing I did helped, or made it worse. Since then I've kept the controller turned off and peak boost is usually around 7-8psi, but it is still inconsistent and it feels like it pulls hard, then slacks off. At this point my vacuum reading at idle on my pillar gauge was pegged out, over 30 in/hg. The PRofec said -9.9 at idle.

Last night I had a guy help me with a boost leak test. He knows 240s more than I do, and noticed that my MAF connector was ziptied. He told me that it needs to be replaced, and is a common problem with 240s. More on this later.

When I did the boost leak test, I took off the filter and MAF, and pressurized the system using the PVC cap method that I've seen many people talk about. I didn't cap off the cold pipe end, couldn't remember if this was recommended or not. Using an air hose, I pressurized the system to about 10-12psi (tried to keep it below 10psi, air hose didn't have an adjustable regulator). It leaked down super fast, but the only leak I heard sounded like it was going past the TB into the engine. I repeated this 2 or 3 times, and couldn't hear any air escaping anywhere else but at the TB. I also don't think it was leaking out into atmosphere, but I'm not certain. It leaked down too fast for me to be sure.

Today, I noticed some changes. The car seems to shudder at lower RPMs, and when I try to hit the gas and go faster, it will shudder for a few more seconds and finally spring to life and go into boost. My vacuum readings have also changed, 27-28 in/hg on the boost gauge, and -8.9 on the PRofec. I did notice that the connector for the MAF was a little loose, do you think this would cause these problems? Why do you think my vacuum readings have changed?

I don't know if it is throwing any codes, the CEL doesn't work. None of the lights on that side of the cluster work. I'm assuming the previous owner unplugged them. I need to fix this, eventually.

Also, there is an AEM UEGO wideband installed in the car, but it isn't installed properly. I think he tried to use the "door ajar" ground as a ground, because the door light stays on constantly, and when you open the door the gauge turns off. It doesn't read properly, it flashes on and off and the readings bounce from 14-17, then randomly it will turn itself off and reset, counts from 1-10 and flashes some weird codes, then goes back to reading 14-17. Does this over and over. I noticed the location of the wideband sensor while I was under the car, but I didn't notice an o2 sensor installed anywhere. Maybe I didn't look hard enough, or maybe the idiot just took out the o2 sensor for the wideband gauge. I haven't had time to figure out this issue yet, but fall break is coming up and I may be able to work on it then.

Sorry for the novel, I just wanted to make sure I covered everything I could think of.

ultimateirving
10-11-2011, 08:52 PM
boost leak will cause all ur boost fluctuations, it should not leak out fast after prssurized. so fix that issue first as it will wreak the most havoc. See if fixing the boost leak if it fixes ur idle issues as well(vacuum leak could cause ur issues)
check back in after u've fixed the leaks.

triumph_013
10-11-2011, 09:04 PM
boost leak will cause all ur boost fluctuations, it should not leak out fast after prssurized. so fix that issue first as it will wreak the most havoc. See if fixing the boost leak if it fixes ur idle issues as well(vacuum leak could cause ur issues)
check back in after u've fixed the leaks.

Well, like I said, I couldn't find any leaks to atmosphere. It sounded like the air was going past the TB into the engine. I plan to cap off the cold pipe and retest sometime this week

triumph_013
10-12-2011, 10:14 PM
Ok, I did the boost leak test again capping off the cold pipe at the TB, and I think I may have did something wrong, or I have a big problem. Nothing happened. I could tell that it was getting some pressure because the intake was expanding, but my friend sitting in the car said the boost gauge didn't move. It wasn't holding pressure at all, and I didn't hear any leaks. I was testing from the intake by taking the filter and MAF off, should I remove the intake completely and test from the turbo inlet?

cotbu
10-13-2011, 12:02 AM
The boost leak test is to test the intercooler and piping. You don't what to pressurize the crankcase. So block off, IACV, hose, valve cover Tee to intake hose, you can leave you BOV recirc'd.
I know some people boostleak test, without capping those off, but they're doing it wrong.
And something is wrong if your dip stick doesn't pop out! XD!

You also shouldn't be leaking past the throttle body, if you are look and see if it's fully closed.
This would also make me check the tps voltage, because tps close signal would be wrong. DUH!

triumph_013
10-13-2011, 12:30 AM
The boost leak test is to test the intercooler and piping. You don't what to pressurize the crankcase. So block off, IACV, hose, valve cover Tee to intake hose, you can leave you BOV recirc'd.
I know some people boostleak test, without capping those off, but they're doing it wrong.
And something is wrong if your dip stick doesn't pop out! XD!

You also shouldn't be leaking past the throttle body, if you are look and see if it's fully closed.
This would also make me check the tps voltage, because tps close signal would be wrong. DUH!

Well I blocked off the IC piping at the TB, and it still wouldn't hold pressure. And I didn't hear any leaks. It's like the air went out as fast as it went in, or I did it wrong. The BOV is vented to atmosphere

I was kinda pushed for time when I did it tonight. I may have more time to mess around with it tomorrow. Kinda hard to work on my car when I'm using tools out of the Formula SAE garage here on campus, not sure if I'm allowed to do that or not haha. Fall break is coming up, may have to wait til then