‘90 GSX

[Yaakob]

This is the Build Thread for ‘90 GSX. Reply below.

 

[Yaakob]

Ill start this off by saying I almost strictly lurk on forums. I love using them for information and such but I’ve never been someone who gets super involved in it. However, I will try to keep this somewhat active even though progress will be very slow due to recently getting engaged. So the fiancé is much less keen about me spending car part money and much more interested in saving for a wedding. Weird.

Anyways, I bought the GSX about 2 months ago, picked it up locally for what seemed like a pretty good deal. Coming from Maine, we don't tend to see a lot of local gsx’s and ones that are around are either kept forever by their owners or completely rotted out. So when this one came up for sale I pretty much bought it hours after it went up. Its decently clean, obviously needs paint work, but super clean interior and mostly rust free with a pretty good little mod list to boot.

At the time of purchase it had 133K original miles and a fp manifold, evo III 16g, kelford 272’s with stock cam gears, precision 780s and just your other general supporting mods. (Fuelab fpr with -an lines, wally 255 rewired, afr gauge, fmic etc etc) it was “street tuned” by the previous owners buddy allegedly at 23psi. Which honestly had me a little concerned since that sounds a little bit like a recipe for disaster. Regardless i picked the car up, drove it 40 miles home without a hitch.

So that was that, right? Fun little gsx that makes somewhere around ~300hp that I can have fun with for the summer before working on it in the winter? Well no. About 2 weeks into ownership it started to throw the CEL randomly. A little bit of digging and I found I was getting some pretty good knock spikes, so as a quick fix I started pulling a bit of timing out on the top end to see if that could help. Unfortunately it did not. So I did what I thought would be best and started the process of getting it retuned. Reached out to Sixsigma and Kevin took a look at the logs. He determined Im having fueling issues, primarily running lean at the top end. So after some discussion I set off to absolutely confirm that there is in fact a Walboro 255 installed, cause you never know. While doing this i took a look at all the fuel lines or anything that could potentially look damaged or the cause of the issue. I found a nasty oil leak from what I can only assume is the oil pan, but other then that things looked pretty good, and I was once again surprised by how (generally) rust free the car is for spending 30+ years in the Northeast. So much so that I’m convinced between the paint fade and lack of car cancer, that the car spent a lot of time down south. All in all, there was a 255 installed. Which honestly was a bit disheartening because I would have much rather spent a few hundred dollars to throw a 255 in it, rewire it and be back on the road

So whats next. Well, Kevin and I decided on swapping out the fpr gauge for a fuel pressure sensor. At least that way we can datalog all fuel stuff and going forward it will be a good tool to have, and can also help determine the issue at hand. So I went and ordered an aem 0-100psi fuel pressure sensor. It arrived last weekend and so i set out to install it. Using images on the forums and the ECMLink mfi, I ended up using the no longer utilized EGR sensor, as well as the standard 5v power and sensors ground.

Once that was all soldered, heat shrunk and wired, I plugged it into the sensor and tossed autometer 2246 into my displayed values. Excited that we were going to possibly be getting answers to my fuel problems soon. However the car had another plan. No reading on the sensor. Of course, i must have wired something wrong. So myself, being the way I am, I pulled it all out and did it all over again. This time I also cleaned up a bunch of things and used non conducting butt connectors because my soldering iron is old and awful, and I had a feeling it might have been the reason for the sensor not reading. However, once all finished, again no reading on the sensor. Just a constant 99psi. So again with the help of Kevin, we looked into what could possibly be going on. After a few hours of trouble shooting we determined that the sensor was receiving only 4.47v of power while plugged in, and while unplugged, we were only getting 4.49v. So not the 5v power were looking for. And that is sort of where the first update comes to a close. Further back from where we started just due to seemingly very unfortunate situations, and 30 year old cars. Not only has the fuel issue not been sorted but now its a matter of fighting other issues that are prohibiting us from determining what is causing the fuel issue in the first place.

Next step for this week is to order up a GM LT1 tps pigtail connector, and see if possibly that could give us some sort of different reading. Then after that hopefully continue forward and get the car back to a happy, safe and reliable state to finish out the summer.

 

[Yaakob]

Not much to really update, got the GM tps sensor installed and wired with no luck. So still trying to figure out why I'm only reading 4.47v

 

[yokotabrat]

Maybe we can help you figure it out. Where are you measuring 4.47V and how are you measuring it? I'm assuming you have 3 wires connected to the sensor (sensor 5V from ecu, sensor ground from ecu, and EGR input)? Are you measuring 4.47V from sensor 5V to sensor ground? You wouldn't happen to be measuring to chassis ground instead would you?

 

[Yaakob]

Maybe we can help you figure it out. Where are you measuring 4.47V and how are you measuring it? I'm assuming you have 3 wires connected to the sensor (sensor 5V from ecu, sensor ground from ecu, and EGR input)? Are you measuring 4.47V from sensor 5V to sensor ground? You wouldn't happen to be measuring to chassis ground instead would you?

So the 4.47v is coming from the raw egt voltage imput on ECMlink. When i throw a multimeter on 5v power to sensor ground i get a full 5v reading. The 4.47v is only being read on ecmlink, everything else looks to be fine. I checked the pins through the ecu to verify that they are the correct ones, tried a different sensor to rule out that i might have gotten a DOA sensor. Im not sure if it could be something within ECMlink thats not reading properly? Or possibly something else.

 

[yokotabrat]

So the 4.47v is coming from the raw egt voltage imput on ECMlink. When i throw a multimeter on 5v power to sensor ground i get a full 5v reading. The 4.47v is only being read on ecmlink, everything else looks to be fine. I checked the pins through the ecu to verify that they are the correct ones, tried a different sensor to rule out that i might have gotten a DOA sensor. Im not sure if it could be something within ECMlink thats not reading properly? Or possibly something else.

Ok, good, so sensor power is verified good. And you verified that the autometer sensor output is going to pin 15 on the ECU? A good test to try would be to remove the autometer sensor output from the ecu and just measure it with a multimeter by itself. It should follow this table that shows output voltage vs pressure:

Sensor Specifications

www.autometer.com

This will tell us if it's something with the sensor or the ecu.

 

[Yaakob]

Ok, good, so sensor power is verified good. And you verified that the autometer sensor output is going to pin 15 on the ECU? A good test to try would be to remove the autometer sensor output from the ecu and just measure it with a multimeter by itself. It should follow this table that shows output voltage vs pressure:

Sensor Specifications

www.autometer.com

This will tell us if it's something with the sensor or the ecu.

So i shot continuity from sensor output to pin 15. And it does not have continuity. So i guess this means i have a break somewhere, or theres another blue yellow wire that ive tapped into guess ill have to look into this weekend

 

[yokotabrat]

Haha! Let us know what you find.

 

[Xarzor]

For your knock issue. What psi of boost are you running and what level of octane are you running in your fuel? Also have you set your AFPR to the correct psi? I don't know this forsure but I heard the 1G knock sensors are trash, possible phantom knock?

 

[yokotabrat]

I think the 1g knock sensors work fairly well. They can get a little overactive when the black silicone on the backside starts to fail but other than that I've not really seen issues with them that couldn't be explained by something external like lifters.

 

[Yaakob]

For your knock issue. What psi of boost are you running and what level of octane are you running in your fuel? Also have you set your AFPR to the correct psi? I don't know this forsure but I heard the 1G knock sensors are trash, possible phantom knock?

Per the previous owner it was “street tuned” at 23psi. I dont know who was the tuner before, I think it was possibly one of his friends. Regardless i backed out the mbc a bit and im right around 18psi on 93. I set the AFPR to 42psi pre vacuum and post vacuum if i remember correctly it settled somewhere around 36-38psi (cant remember exactly). Kevin Jewer has been working on a retune with me and from the logs I've sent him it seems to be fuel starving occasionally. We’ve yet to really trouble shoot the fuel starve since ive been dealing with the fuel pressure sensor issue

 

[Yaakob]

Haha! Let us know what you find.

Well after a little bit longer of poking around at it this weekend i finally found the issue. As dumb and simple as it may be, i ended up bypassing that original blue/yellow wire and just ran signal input straight into the ecu and it works perfectly now. So there must have been a break somewhere in the original wire

 

[jdub099]

While it may seem aesthetically right, your plug wires are ran wrong. The little arrows in the valley are there for a reason and they guide you to keeping one pair of wires away from the other. 1 and 4 should be on the passenger side of the rubber grommet and run along the top of the valley. 2 and 3 should be on the driver side of the grommet and ran along the bottom of the valley. 1+4 and 2+3 should be kept away from each other as much as possible. This prevents crossfire due to inductance. Maybe it matters, maybe it doesn't, but I'd personally do it right.

 

[Yaakob]

While it may seem aesthetically right, your plug wires are ran wrong. The little arrows in the valley are there for a reason and they guide you to keeping one pair of wires away from the other. 1 and 4 should be on the passenger side of the rubber grommet and run along the top of the valley. 2 and 3 should be on the driver side of the grommet and ran along the bottom of the valley. 1+4 and 2+3 should be kept away from each other as much as possible. This prevents crossfire due to inductance. Maybe it matters, maybe it doesn't, but I'd personally do it right.

Interesting, i havent looked at the plug wires since i bought it. Ill have to take a look at then tomorrow