Troubleshooting fuel injection

[3A-C Power]

This pertains to a corolla, so I put it in off-topic. I want to keep this board focused on AL25 model Tercel wagons which I still uphold as the best car in the world.

My problem is, in all it's fuel-injected splendour, my new Corolla with the 4A-FE engine bucks and hesitates at low throttle while cruising and accelerating. In fact it does so more than my carbed Tercel did. The Tercel only did it in the winter while it was still cold. The Corolla does it alot when it's cold but even still when it's warm. It occurs randomly. The engine cuts out for a second, just enough to cause a big jerk. The car drives like a dream other than for this one problem.

I can't find a board dedicated to these engines, it's either this one or the 4A-GE boards.

I know it could be alot of things - O2 sensor, throttle position sensor, fuel pump, dirty injectors or anything and I don't know where to start.

[GTSSportCoupe]

I'd just make sure that you have the engine well maintained, and take it from there.

I'd put in new plugs, cap and rotor. Make sure timing and idle speed are set right. No vacuum lines disconnected or leaking, good thermostat, etc.

The throttle bodies and injectors tend to get super dirty on many of the early EFI Toyota engines due to the EGR and PCV.

Remove the fuel injectors and soak them in carb cleaner, then brush the crud off with a tooth brush while being careful not to poke any up into the nozzle. Rinse them so they are perfectly clean and nothing is stuck in the little screen filter area. Then put them back in. This will help lots.

If you are feeling more adventuresome, remove the entire throttle body/intake manifold and clean it up really well. Try not to affect the adjustment of the TPS as you take things apart.

One of the main things you can do, is check your diagnostic codes. Simply turn the key to the on position, and short T1 E (I think, or T to E1), in the little diagnostic connector thing in your engine bay. It should make your engine light blink on and off slowly. If it does any sort of pattern, then it is trying to tell you a code. The codes are probably the same as the same generation 4age engines.

Amongst Toyota OBD EFI engines, pretty much everything is the same. Try Dori-Kaze.com if you are looking for more info. They are Canadian, and quite helpful.

After all this, check the oxygen sensor, temp sensors, tps, grounds, ignition system, etc, etc.

[3A-C Power]

Thanks. I thought you would respond. I have alot of the (only) previous owner's repair records, and he did alot of maintenance. He got the fuel injectors cleaned a few times and changed the spark plugs, fuel filter, wires etc. I'll do the cleaning you suggested since it's free, and I'm still waiting for a factory service manual to give me the numbers for all the sensor tests. Does the ECU ever give codes without the engine light coming on? I had a look at the haynes manual at the library, and it's such crap it's not worth paying my library fine to take it out. For the EFI section it just says to do a basic check or else take it to an authorized dealer. Screw Haynes.

[GTSSportCoupe]

Thanks.  I thought you would respond.  I have alot of the (only) previous owner's repair records, and he did alot of maintenance.  He got the fuel injectors cleaned a few times and changed the spark plugs, fuel filter, wires etc.  I'll do the cleaning you suggested since it's free, and I'm still waiting for a factory service manual to give me the numbers for all the sensor tests.  Does the ECU ever give codes without the engine light coming on?  I had a look at the haynes manual at the library, and it's such crap it's not worth paying my library fine to take it out.  For the EFI section it just says to do a basic check or else take it to an authorized dealer.  Screw Haynes.

Haha! Yeah, the Haynes manuals do really suck.

The ECU on the OBD 1 engines only ever gives codes through the check engine light when the car is in diagnostic mode (when you have the T1 and E jumpered).

Although, I think some of the later Cressidas/Supras showed the codes on the radio display...definitely not on the Corollas though.

You'll find that EFI is actually really quite easy to troubleshoot when you have little running hiccups like you have now. EFI is so easy compared to carbs for this sort of stuff.

It's possible your fuel pump is having issues too?

The problem sounds definitely like fuel to me...possibly ignition issues, but that seems less likely.

I may already have sent you this link, but if you'd like to learn more about EFI engines, read these Toyota pdfs:

<a href='http://www.autoshop101.com/techarticles ... icles.html' target='_blank'>http://www.autoshop101.com/techarticles ... es.html</a>

(specifically the OBD 1 articles). You'll learn tonnes about Toyota EFI stuff.

[Mac]

sounds like eletrical.

however, since its electronic fuel injection, it should have some way of reading the ECU so it can tell you a code or something.

[hornett22]

most likely your TPS is bad.then,how are the plug wires? when you pull them out of the head is there oil down around the plug?is the end of the plug wire wet with oil?
leaking valve covers like the ones on this motor will ruin plug wires.

[3A-C Power]

Plug wires are fine and there's no sign of oil in there. Plugs themselves look great too. It only seems to screw up at low throttle either cruising or gently accelerating. It's fine when I step on it, but for practical reasons I can't step on it all the time.

[takza]

Plug wires are fine and there's no sign of oil in there. Plugs themselves look great too. It only seems to screw up at low throttle either cruising or gently accelerating. It's fine when I step on it, but for practical reasons I can't step on it all the time.

Vacuum leak...too much EGR?

[3A-C Power]

It fixed itself, for now at least. You're right - troubleshooting EFI is easier.
I checked the ECU and found only the normal code, and verified that the air/fuel correction factor is normal and it's running in closed loop with the O2 sensor swinging its voltage at least 8 times in 10 seconds at 2500 rpm. Then I disconnected and connected some vacuum hoses on the EGR valve and also one connection. Nothing seems abnormal. This morning when I drove it, there was no hesitation. I'm sure it will come back and I'll have to troubleshoot in depth.

[Chris]

What year is your Corolla? I have a FSM for the '91s if you need any info from it

[3A-C Power]

It's a 92, same as the 91.

[takza]

This morning when I drove it, there was no hesitation. I'm sure it will come back and I'll have to troubleshoot in depth.

Go thru it and check vac and elect connxs...you might have fixed something...for now?

[3A-C Power]

I disconnected the EGR valve and that made it better. So now I'm asking myself is the EGR going on too much or is it some other problem that makes the engine extremely sensitive to EGR? What does EGR really do for us anyway? I've heard the engine can run too hot without it, but isn't running with a percentage of hot exhaust gas just the same as running with less fuel and less air except that with EGR you get residual heat being pumped back into the engine? I've never understood the logic. My temperature is normal without EGR. I'd rather pollute less if it really makes a difference.

[3A-C Power]

It was good for a while then gradually it started screwing up even with the EGR disconnected. I don't think that's really the issue then.

It's worse when cold. Sometimes when it's been running for a while it gets to the point when it runs normal. After cold startups it's always really bad. Some days are worse than others. When the gas tank is almost empty, it gets noticeably worse.

Do fuel injectors ever just go bad, or do they only get dirty?

[takza]

Fuel pump or pressure regulator...filter? Manifold gaskets?

Try 3 oz per 10 G (US) acetone...it will clean the injectors over time and you get better mileage to boot.