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Runs lean after cleaning the injectors

Hello everyone. i have some stumbling/missing in the engine.
it happens only while idling. As it warms up and the fast idle disengages, it will start stumbling when the rpm drops below 950 and becomes pronounced when it’s at 800.
it started when i cleaned the injectors.
the codes are:
P0300 - random misfire
P030x - misfire in cylinder x (all 4)
P0171 - system too lean
so i turned up the idle a bit but i can’t seem to fix the problem.
i cleaned the MAF with some carb spray.
fixed a tiny vacuum leak. to no avail.
no codes about O2 sensor.
toyota people used unique fuel line fittings cause they think i’m too dumb to check the pressure. good work fellas.
any ideas? thanx

Start with a fuel rail pressure check probably. You might get lucky and there’s something wrong w/the fuel pressure regulator ( FPR). Find that part somehow, usually it is near the fuel rail. There should be a vacuum hose on it that goes to the intake manifold. Make sure that hose is in good shape, no hose leaks, and solid connections at both ends. Good idea to make sure you or someone didn’t accidentally route that hose to the wrong place btw. Now remove that hose from the FPR end. Any signs of gasoline inside the hose or in the FPR where the hose plugged to? If so, the FPR diaphragm is leaking. Replace the FPR.

well that’s a good suggestion and i did that, but it didn’t tell me anything. i fabricated a tool to disconnect the fuel line and took a pressure reading. it was a steady 47#s. when i goosed the throttle the needle move a teeny bit like about a 1/2#. as for the FPR, it’s a 2003 Matrix and the FPR is inside the tank. i guess that’s why the pressure doesn’t rise and fall like in most cars.
so it’s a bit of a mystery. i have the idle turned up a bit to remedy the situation but i’d still like to fix the problem.
thanx for the reply :slight_smile:

47 pounds sounds about right w/engine idling for Toyota fuel injection fuel rail pressure. I’m seeing a spec of 44-50 psi for the 1.8 L 1ZZFE, which is the engine I presume you have. So you are right in the middle. I don’t see that as a problem. It appears it should remain at least 21 psi for 5 minutes after turning off the engine btw, so since you are all set up for that measurement you might as well do it.

The rail fuel pressure on my 4afe equipped Corolla goes up noticeably when I open the throttle. You’re only seeing it go up 1/2 pound? That might be a problem. Here’s why. The amount of fuel injected (for a given injector pulse length) is proportional to the difference in the fuel pressure and the intake manifold pressure. At idle the intake manifold is around -20 inches of mercury which is about -10 psi. So the total pressure difference when you measure 47 psi is 57 psi according to what the injectors see. When you open the throttle the intake manifold might go to -5 psi. So then the total difference according to the injectors should be 52 psi. but that’s too low, you’d get a lean condition. so the rail fuel pressure is supposed to go up to 52 psi, yielding 52 + 5 = 57 psi according to the injectors, same as at idle.

So one idea, that low level of fuel pressure increase you’re seeing when opening the throttle might explain the lean condition. However I’m just a driveway diy’er and I’m not familiar w/ the fuel pressure regulator being a part of the fuel pump ass’y. So yours may work differently w/respect to how it handles the throttle vs fuel pressure function. Maybe somebody here understands that and will chime in. If you have a way to measure fuel trim you could measure it at idle vs at a higher rpm. If it went considerably leaner at higher rpms, that would be consistent the fuel pressure vs throttle function being off kilter.

If the lean code and misfires aren’t a fuel pressure problem … hmm … since it started w/an injector cleaning, how exactly did you clean the injectors? Perhaps it dislodged gunk somewhere which has now reclogged the injectors, only worse. that would produce a lean condition. An injector volume test and/or injector balance test might show that.

Edit: Toyota has issues a TSB for the proper fuel injector cleaning procedure btw, PG011-05.

that’s a good idea i’ll recheck that tomorrow.
i would think that the brain would read the map sensor and compensate for lower vacuum levels by trimming up the injector pulse. But whatever, it seems to run just fine at WOT. and when it’s at idle, the codes are saying that all 4 are running lean.
when cleaning the injectors i did what i saw on youtube, with a can of carb spray and a tube adapter, i took each one and hotwired it to the battery while squirting the solvent through it. maybe 4 seconds on each one.
and i just ordered a cheap chinese scanner on ebay that can supposedly show fuel trim, but it’ll take a month to get.
*THANX GEORGE* for that info. it really helps. i’ll keep workin on it and post back what i find.

Here’s the Toyota TSB mentioned above

If your tests confirm a lean problem at idle but mixture ok at higher rpms, that would point to clogged injectors or a vacuum leak somewhere. Suggest to check for any vacuum leaks in

  • PCV system
  • EGR system
  • Brake power booster

There’s may be some things called SVP’s (switched vacuum ports) that can cause vacuum leaks too. One may be the power steering pump. Anything that increases the idle speed by allowing extra air into the engine is suspect. Switching on headlights, turning the steering wheel, rear window defroster, radiator fan are all things that can cause rpms to automatically increase to prevent stalling. How it all works depends on the car’s design.

I don’t mean to sound rude, but you went about it the wrong way

This is what you’re supposed to use

You are not supposed to hotwire the injectors, either

EFI injectors are pulsed, they don’t spray continuously

I hate to say it, but IMO there’s a fair possibility you actually caused some problems with your youtube cleaning method

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@db4690 … do you know how this car’s design with the fuel pressure regulator in the fuel pump, how does it compensate fuel delivery rate for throttle open/closed? On my Corolla that’s done with the fuel pressure regulator vacuum connection to the intake manifold. But how it the same function accomplished when the fuel pressure is set at the fuel pump in the tank?

well if i can find something like that… i think i have a vacuum gage somewhere in the trash heap of my garage, and i can check those other things, too. and the… uh what’s it called… the idle air solenoid? idle air control? that thing. we’ll see…

i’ll check the resistance and inductance of the injectors, although it doesn’t seem that plausable when i only had them open for a second or two at a time. still it’s possible. but it’s not possible for me to get one of those tools.