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Fuel trims really high and no boost leaks?

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EagleTalonTim

15+ Year Contributor
833
13
Jan 10, 2007
Brighton, Tennessee
I have been battling with my fuel trims since I got this car. Here is my set up :

93 Eagle Talon A/T
Manual Shift Box
JDM 4G63T
Stock SMIC
Stock IC piping
Stock Fuel pump rewired
Evo III 16g
450 Injectors
M/T ECU to run the 450 injectors
SAFC2
Datalogger with MMCD

First off, I just installed a brand new O2 sensor today and I still cannot get it to read over .85v at WOT. I replaced the old one because I could not get it to go over .83v at WOT. It did not help at all. My fuel trims are outrageously high.

Low : 139%
Mid : 106%
High : 130%

Fisrt, I turned my SAFC up to +15% at 1000 RPM to try and get my FT02 to around 100%. The best I could get was 103%. I am worried about adding more fuel because my gas mileage already sucks. I then reset the fuel trims and zeroed everything out to see what would happen and 1 hour later, the fuel trims were back over 120% again. After changing the SAFC to +18% @ 1000 RPM and reset the ECU again, the fuel trims started going back up yet again. What is going on? The M/T ECU is supposed to be programmed for 450 injectors. I stay out of boost most of the time to keep the gas mileage as best as possible. I have set the AFPR to 48psi at idle with the vacuum line disconnected hoping to drop the fuel trims more. Nothing has worked so far. I pulled the ECU out of the car and checked for leaking caps and there was no problems at all on the board. I really need help getting this thing running right. Any input would greatly be appreciated. I am tired of buying parts for this car to hope it fixes something I can't quite get right.
 
hmm just noticed in your post.....48psi at idle???? You could be overrunning your injectors. I was under the understanding that 450 is stock in a 1g.

The EVOIII default wg spring being 1bar(14.7psi), 3-4psi higher than stock turbo I'd think you'd need to take air away rather than adding it...-5% or so should be a good starting point. When I had the SAFC with my EVOIII and 550's I was taking away 18-22% never did I need to add.
 
Also, correct me if I'm wrong here but if your TPS is not bang on and the ECU never really sees WOT, the O2 would never go open loop therefore never showing you 1v....right?

I'd check and adjust the TPS if needed.
 
The TPS never reaches 100%. It reaches at best 98.9 but if I adjust the TPS to go to 100% at WOT, the CEL comes on which is a faulty TPS code.

Edit :
The fuel pressure without the vacuum line before was at 37psi. I turned it up to try and get the FTO2 around 100%. I did notice that the fuel pressure dropped a little after revving really fast. Would this mean a weak fuel pump?
 
Are you able to use the stock FPR still?

If so, I'd try that, zero out the SAFC and look at the trims then.

Seeing as 450's are stock and there is no boost at idle therefore airflow should be the same as with a stock turbo (not like it matters for idle but anyway) and I'd expect to see trims that require very little compensation to dial in. If they are still way out there, I'd almost start suspecting a bad ECU seeing as you replaced the O2 already and the TPS seems to be fine.

However, the TPS throwing a code when you get it to read 100% has me a little baffled.
 
I will be messing with it tomorrow. Before I put the AFPR on, I had a friend hook up a Fuel Pressure Gauge and see what the pressure was. With the vacuum line off, it was 43psi. I was told to set it at 37 since my car was originally running really rich. I am thinking it is either the fuel pump getting weak or the MAF not reading right. If I can figure out how to mount and pipe the 2g MAF, I would install it and adjust the SAFC to compensate for the 450's if possible. I have a friend who has 550's but I would rather spend the money on 650's instead since I am aiming for a higher HP level.
 
37psi with vaccuum off is the stock fuel pressure. It should be around 27psi with the line on.

But really, with 450's the SAFC should be at 0 with 37psi of pressure with the line off. That would make it completely stock.

Of course raising the fuel pressure will make you have to adjust the SAFC.

That's where I'd start and eliminate from there.
 
ok, I reset everything....I reset the ECU, Zeroed out the SAFC on both High and Low throttle, TPS (99.6% WOT), Biss Screw, Timing (5°), and Fuel Pressure (38psi w/o vacuum line). Now, my FT02 is up to 165% at idle and it stays around 145% while driving normal. I have no idea what to do now :( As soon as I can get my MMCD software to work right, I will post my latest log.
 
Hey tim. I am having the exact same problem with my car as you are. Only I have 550's and 2g mas currently installed. Mine and your logs are almost identical. After trying numerous things...the only conclusion I can make is that there is an exhaust leak at or around the turbo alowing the o2 to see more oxygen than the motor is actually seeing. I have learned to live with it as long as my timing is right and there is no knock. Im currently ar 16 psi and the car runs great aside from the 02 readouts being extremely irratic (sometimes I feel the car start really dragging and doesnt run right...look at the the logger and o2 volts are .00:|) Im at a loss. I thought originally it was a bad o2. Changed the o2 sesor and still the same thing...even when the car was bone stock its low trim was 139 so I just take that as a way of the beast. Like I said I just have learned o deal with it and pull the negative battery terminal every couple times out. Time for an eprom and keydiver imho for the both of us.

Greg
 
I do have a crack in the stock 1g manifold. I had to use a 14b manifold because the original manifold that was on the car only fit the 13g which originally came on it. Maybe the crack is enough to make the O2 read funny. Is there any temporary fixes for the crack? It will be awhile before i can afford another manifold. I have one that I like in mind, but it will take several months of saving to get it.
 
I do have a crack in the stock 1g manifold. I had to use a 14b manifold because the original manifold that was on the car only fit the 13g which originally came on it. Maybe the crack is enough to make the O2 read funny. Is there any temporary fixes for the crack? It will be awhile before i can afford another manifold. I have one that I like in mind, but it will take several months of saving to get it.


A crack in the manifold will give the problems that you are having. As far as the tps only going to 99.6 is fine, the ecu is in open loop at 90% or more.

I would buy a 2g manifold for 30-50 dollars and invest in ECMLink.

Steveb
 
I would be looking at your Front O2 sensor as the problem. It just doesn't seem to be cycling properly. I'm seeing a bunch of 0.08v data points and a very small number of points above 0.7v, or so. Typically, things should be cycling between 0.2v and 0.8v. It's also reading really lean at WOT, seeing that you are adding 15% additional fuel with the SAFC.

How old is the front O2?
 
I still have the stock MAF with the 450's and the M/T ECU. I have read that I need to upgrade injectors at the same time with the 2g MAF since it flows about 50% more. Since the MAF is not needed at the moment, I have held off on installing it. Before I mess with anything else, I need to get me a Walbro 190 or 255, then the fuel injectors.
 
I still have the stock MAF with the 450's and the M/T ECU. I have read that I need to upgrade injectors at the same time with the 2g MAF since it flows about 50% more. Since the MAF is not needed at the moment, I have held off on installing it. Before I mess with anything else, I need to get me a Walbro 190 or 255, then the fuel injectors.

Right on. Remember that if you get a 255 then you'll need to get an adjustable fpr also. If you don't plan on more than 400hp a rewired 190 will be fine. Some like the 255 for insurance though, and an adjustable fpr is good for fine tuning, but it's quite a bit of money.

Also I just thought of something, you might want to check your base fuel pressure, having too little will cause your ecu to add fuel and change your fuel trims.
 
I just put a ground wire on the O2 dump to the frame and it looks like that may have sort of fixed my problem. Instead of a 139% with the SAFC at 0% correction, the Low trim is now around 108%. With the SAFC set at +4% it floats right around 100%. Another problem I am running into is that even with a 192° t-stat, my engine temp hardly ever gets over 182°. What would cause this?
 
I just put a ground wire on the O2 dump to the frame and it looks like that may have sort of fixed my problem. Instead of a 139% with the SAFC at 0% correction, the Low trim is now around 108%. With the SAFC set at +4% it floats right around 100%.

Sweetness.

Another problem I am running into is that even with a 192° t-stat, my engine temp hardly ever gets over 182°. What would cause this?

Check your coolant level. Could also be your CTS (coolant temp sensor) giving a bad reading, it's located on the side of the t-stat housing.

EDIT: Have you ever done a boost leak test to check for vacuum leaks? What is your vacuum at idle?
 
I may need a new ECU side coolant temp sensor but I don't have the money right now. The coolant level is even with the cap after cooled down. I have done several boost leak tests and I only have 1 which is the valve guide seals. It leaks about 1 pound every 20 to 25 seconds. I have not done a boost leak test with the engine at higher temps lately. The last one made the valve guide seals actually seal better. The vacuum at idle in Park sits at 20 to 22 inHg. In Drive, it goes up to about 18 inHg
 
It leaks about 1 pound every 20 to 25 seconds. I have not done a boost leak test with the engine at higher temps lately.

That's excellent!! I've never heard of results that good actually. It's usually a psi every 5 seconds or so. Vacuum is awesome also. You don't have any leaks that's for sure.
 
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