Swap running very lean. Help Please.

Hi Everyone!

I purchased a ST185 with a blown motor back in September. In October, after a lot of research and finding a good deal, I purchased a ST205 WRC swap for it. After 6 months of cursing and looking at electrical diagrams, I finally got the car running. Initially I couldn't get it to boost over 5lbs, but it had a CEL for the Intercooler pump. I managed to go back in and play with wires and get the intercooler pump functioning properly and the CEL went away. I read up on the troubleshooting and managed to figure out why the car wouldn't boost over 5lbs, I've been so frustrated lately that I've completely forgotten why it wouldn't, a valve was bad on the car that I had to replace and I also installed a manual boost controller. I only had the boost set at 10psi (per my boost gauge) because I had to order and AFR and Water Temp (stock is not working) gauge. I decided to take it to my friend's shop yesterday to monitor AFR and such to crank the boost and see what the car would do. I figured with the DynoPak he has, I can at least monitor AFR, which is the biggest thing I was worried about.

Upon strapping the car to the dyno, first pull was 191.97 AWHP 185.22 AWT. Before we adjusted the boost controller, we decided to look over the graph and I'm getting an abnormal AFR so I'd like some advice. The car is running very lean. From about 2k RPMs when the turbo is starting to build boost, until about 4800 RPMs where I'm at about 7psi, the AFR is stays at about 15.35, then goes down to about 13:1 by 5500 and finishing at about 12:1 by the time i'm at redline. I'm working on getting my friend to email me a copy of the chart so I can post it for you to check out. I'm in a rut and really don't know where to even start. I know the basics to engines, how they work, and where things should be. I have a 91 MR2 with a JDM 3SGTE and CT27 turbo that I did everything on and I've never had any issues or things to monitor.

What i'm really looking for is just some guidance. I planned on checking fuel pressure and fuel pump when I get a chance, but then part of me says if that was bad, i would be running lead all the way through the RPMs, not just the mid-range. The last thing I want to happen is to experience detonation and have to put the car out of commission until I'm able to fix it. I really am in love with this car. This was supposed to be my project and ever since I got it running I haven't driven my car i'm making payments on haha. I also was going to look and see if I had a bad ground somewhere and the ECU isn't reading the map correctly, but I moreso wanted to see if you guys have any insight or direction with past experiences on where I should check first. Any help is greatly appreciated.

Thanks!
Josh

Also, for what it's worth, I've got a CEL now for the 02 sensor, which I need to replace. Not sure if this could cause my issue, but I wanted to put it out there. The CEL cuts off whenever I cut the car off and doesn't come back on again until about 30 mins of driving the car again.

Sounds like issues with the fueling system, for starters change the fuel filter out since it's easy and good to do every so often anyways.

Stock wastegate pressure is 7-9psi on the ST205. Without any boost control (and with a happy stock ECU) it should go up to 12-14psi on the stock boost control system. Take off that manual boost controller for now and get to the bottom of your problems first.

Are you using all the stock parts from the ST205? (MAP sensor, injectors, etc.)
Replace that O2 sensor ASAP.

How does it drive at part throttle?

-Charlie

phattyduck":1c5nlmv6 said:

Stock wastegate pressure is 7-9psi on the ST205. Without any boost control (and with a happy stock ECU) it should go up to 12-14psi on the stock boost control system. Take off that manual boost controller for now and get to the bottom of your problems first.

Are you using all the stock parts from the ST205? (MAP sensor, injectors, etc.)
Replace that O2 sensor ASAP.

How does it drive at part throttle?

-Charlie

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Will do, I'll get the boost controller off and see what it does. I am using all stock parts from the 205. The only thing is an ATS Racing 3in Downpipe, 3in exhaust, and I had to make an intake for the car. other than that everything is stock.

The car drives great, It doesn't give me any issues. Pulls great, boosts fine, I just didn't want to really get on it hard until I was able to monitor AFR and water temp.

Does the car have a cat? Where was the O2 sensor when you were checking the AFRs? Do you have an EGT gauge to check how hot the motor is running?

I think it will be fixed when the O2 sensor is fixed...

-Charlie

phattyduck":34rtgz0u said:

Does the car have a cat? Where was the O2 sensor when you were checking the AFRs? Do you have an EGT gauge to check how hot the motor is running?

I think it will be fixed when the O2 sensor is fixed...

-Charlie

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Car doesn't have a cat. The O2 sensor is mounted right on the downpipe. probably about 5 inches from where it bolts to the turbo. I'll have my wideband in next week and when I install it I plan on doing the o2 sensor then also. I do not have an EGT gauge. Just Water Temp, AFR, and Boost.

Where was the wideband lambda mounted when you were on the dyno. With that high afr (16:1) it should hesitate and not run smooth. Are you sure there are no exhaust leaks that could have fooled the wideband. If it leaks out of the exhaust it will also pull fresh air into the exhaust due to pulsation causing the wideband to show lean afr.

Pipedreams":2oa7nz95 said:

Where was the wideband lambda mounted when you were on the dyno. With that high afr (16:1) it should hesitate and not run smooth. Are you sure there are no exhaust leaks that could have fooled the wideband. If it leaks out of the exhaust it will also pull fresh air into the exhaust due to pulsation causing the wideband to show lean afr.

Click to expand...

I'm going to check for an exhaust leak today. I got the graphs and I just realized I typed 16, when it was 15. One of the guys doing the dyno told me how it was running throughout the power ban and now that I got the graphs, it doesn't look as bad as it was explained to me. Not great, but definetly not what I thought it was. Does this look realatively normal? I'm not freaking out as much now, because even though its lean around 2800 rpms until about 4100 RPMs, it seems to get down to 13.5 area around 4300 rpms. Here are the graphs:

Those numbers are exactly what I would expect for a stock dyno pull. The slight lean is from the throttle tip-in at the start of the run. Otherwise, it is stoichiometric for a bit, then gets all the way dow to 'full rich' in the higher rpm's. Sounds fine to me...

-Charlie

phattyduck":1dxabea1 said:

Those numbers are exactly what I would expect for a stock dyno pull. The slight lean is from the throttle tip-in at the start of the run. Otherwise, it is stoichiometric for a bit, then gets all the way dow to 'full rich' in the higher rpm's. Sounds fine to me...

-Charlie

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I've only got it at 10psi right now, would it be safe to turn boost up some on my MBC once i've got the new o2 sensor installed?

clevrname":1eoyl6hh said:

I've only got it at 10psi right now, would it be safe to turn boost up some on my MBC once i've got the new o2 sensor installed?

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The factory boost is 12-15psi, so yeah. I run 14psi daily and 17psi in high-boost mode, and it seems to do fine even on California 91 octane gas. It is much happier with some 100 octane in the tank.

-Charlie

phattyduck":3k0wjf72 said:

clevrname":3k0wjf72 said:

I've only got it at 10psi right now, would it be safe to turn boost up some on my MBC once i've got the new o2 sensor installed?

Click to expand...

The factory boost is 12-15psi, so yeah. I run 14psi daily and 17psi in high-boost mode, and it seems to do fine even on California 91 octane gas. It is much happier with some 100 octane in the tank.

-Charlie

Click to expand...

Awesome, thanks for the help. I was just worried initially because the guy who had it on the dyno said it was really lean and he wasn't comfortable upping the boost until we figured out if there was a problem or if the car is supposed to be like that from the factory.