4th gen 3sgte running really rich

[UtahSleeper]

So, here is a question.

Do the st215's have an ECU that learns at idle/idle circuit? Or a circuit that just deals with idle? I know megasquirt has specific circuits that deal with idle and I know newer cars relearns, but not sure on these ECU's.

I also know that ECU's dont tend to be an issue, but just discuss.

I ask cause cause at idle is when I seem to be having the issues. Revving seems fine on the ECU and driving also seems to give the idea that things are fine. Its only idle.......from the data I can see.

[sergei]

Yes, they do learn, but indirectly, as far as I know. They apply the fuel trim learned from cruising to idle, they also learn the actual idle. Otherwise idle meant to be on the rich side (slight). have you tried adding a small vacuum leak to see if it affect your mixture at idle? Perhaps you have a vacuum leak to start with (although I expected it to be on lean side).

[UtahSleeper]

Yes, they do learn, but indirectly, as far as I know. They apply the fuel trim learned from cruising to idle, they also learn the actual idle. Otherwise idle meant to be on the rich side (slight). have you tried adding a small vacuum leak to see if it affect your mixture at idle? Perhaps you have a vacuum leak to start with (although I expected it to be on lean side).

I haven't tried that and I may as well. Just everything I have heard, since its MAP, a vacuum leak wont cause an issue here. I did try and do a boost leak check and it appeared to lose pressure after I would hit a positive PSI, so I may have been doing something wrong.

[UtahSleeper]

Well, here is another update with no solution.

Ran a compression check. All cylinders appear to be at 150 +/-. Seems low to me, but workable.
Removed the upper timing cover and moved the crank to 0. Both cam gear marks lined up with the back of the timing cover. This motor also had a timing belt done to it before, based on the additional purple markings on the cam gears.

This is what the plugs look like after about 50 something miles. Sorry for some blurry pics, but they all looked about the same.





And here is my previous emissions readings. My last check had about the same results.


Also had my friend rerun an emissions test and the motor is still insanely rich. I averaged 10 mpg out of the last tank.

And here is a recap of everything else done with no changes in behavior.

-Replaced coolant sensor
-Replaced TPS
-Replaced MAP
-Replaced ECU
-Replaced O2 sensor
-Added fuel pressure gauge. At idle, reads 35 psi.
-Ran a fuel rail flush/injector cleaner

And as a quick summary of car:
-ST165 with Caldina engine
-DP from prime mr2
-eBay exhaust
-Walbro FP
-Straight intake
-Some random grounds added to the block

Are there any other sensors I should look at or any other troubleshooting I should be trying? Anyone have any electrical infor where I could verify data coming in and out of the ECU and sensors? Just frustrated cause she drives great and pulls hard(for my experience) but is running too rich.

[MAC_HATER]

This is absolutely puzzling for me, I cant understand how its running so rich after all you have done

the only thing I can think of, is are the injectors standard? Sorry if that has already been gone over I skim read but I didint see anything, it sounds like the injectors have been replaced for some monsters or simply larger CC ones

If they are indeed the standard injectors, or you don't know, it might be worth getting them flow tested and see what they are actually flowing, if they are larger injectors or perhaps not working right and flowing more accidentally as a result, that could be the reasoning behind your crazy rich running

Or, if its easier, find someone with known good standard injectors, swap them over, see what happens? its about the only thing I can think of as you have pretty much ticked everything else off the list!

[sergei]

As reference I flow-tested sky blue caldina injectors, and I got ~540cc/min at ~40psi.

[UtahSleeper]

This is absolutely puzzling for me, I cant understand how its running so rich after all you have done

the only thing I can think of, is are the injectors standard? Sorry if that has already been gone over I skim read but I didint see anything, it sounds like the injectors have been replaced for some monsters or simply larger CC ones

If they are indeed the standard injectors, or you don't know, it might be worth getting them flow tested and see what they are actually flowing, if they are larger injectors or perhaps not working right and flowing more accidentally as a result, that could be the reasoning behind your crazy rich running

Or, if its easier, find someone with known good standard injectors, swap them over, see what happens? its about the only thing I can think of as you have pretty much ticked everything else off the list!

My injectors look standard, but unknown condition. My next plan is to remove them and get them cleaned and tested. Not many other options to check.

[UtahSleeper]

Bump. Still accepting suggestions. Also, any good write ups on testing a harness?

Since the last update here I have:
Got the injectors cleaned(not spec flow testing, but all flow close to each other) and replaced orings and groments
Replaced pcv valve
Tried another ECU

May be more I am forgetting. Only thing I can think now is harness, but not sure since the person who did it has a good rep(wiregap). Just trying to rule out everything.

[UtahSleeper]

Figured I would update.

I believe I found my running rich issue. The sensor for the FPR(located under the manifold). Today I ran a vacuum line from the intake to the FPR(bypass sensor, but leave it connected to the harness) and it appeared to started idling cleaner after it warmed up a little bit. The fuel trim gauge in torque initially showed no data, but after idling a little it seemed the ECU started adjusting the fuel trim. So, not I am going to get a new sensor and see if it behaves correctly.

[MAC_HATER]

Interesting! Keen to hear how it goes for you when you replace that and test again

[sergei]

That "sensor" is not a sensor but a solenoid (aka VSV).
It is for improvement of hot start, it increases the fuel pressure when cranking on hot. It comes on cranking when coolant temp is above certain point and stays on for a few seconds after. The purpose of increase fuel pressure is to prevent percolation (ie: air lock from boiling fuel).

You can bypass that solenoid without problems, as a lot of engines don't run it. It is probably cracked and leaking vacuum (thus increasing the fuel pressure). Although you reported 35psi on idle in the beginning of the thread... Actually what it should be is 36psi (250kPa) higher than the pressure in the manifold. So in reality on idle (moderate vacuum) the pressure should be in mid 20`s. The only way to get 35psi of pressure on idle is for fuel pressure regulator to reference atmospheric pressure (vacuum leak).

[MAC_HATER]

That "sensor" is not a sensor but a solenoid (aka VSV).
It is for improvement of hot start, it increases the fuel pressure when cranking on hot. It comes on cranking when coolant temp is above certain point and stays on for a few seconds after. The purpose of increase fuel pressure is to prevent percolation (ie: air lock from boiling fuel).

That just lit a lightbulb in my own head haha, My corona has massive hard starting issues Only when hot after a long drive, and left to sit for half an hour or so, it will crank for a good 5 or 10 seconds before stumbling and then starting, otherwise its perfectly fine

Ill add that to my list of things to investigate haha

[UtahSleeper]

Guess I never updated lol.

Fixing that sensor got my car running normal. I am not getting the best gas mileage, but it is driveable and passed emissions Still have things to do, but I have been driving her this winter and loving it.

[Bling]

Nice work, good to see you got a good result in the end!