I had an issue months back where the car would hesitate, run very rough, etc once the car was warm. It ran fine cold. I ended up changing the spark plugs, taking out the crappy aftermarket ignition wires, and resetting the ecu..and it went away.

Well it came back randomly. It started as a small misfire after I arrived at work after a 30 min drive. Then gradually become more pronounced the longer the car runs.


I've been able to figure out the miss is at cylinders #1 and #7. I have plenty of spark at the wire, and the plugs are good. Also it seems to run rough much sooner than before. There's no smoke, and I can still actually get the car up to speed, and it will rev up. It just stumbles heavily.

How the issue has reoccurred and how random it is makes me think it's possibly dirty / bad injectors at #1 and #7. Is there a sure way to test them?

 

Scope the current. You can visually see the injector open with the current it uses. You will want to triger off cyl 1 in the ground side and use the EFI fuse with a fused jumper wire to get pattern to watch all the injectors fire. You will need a 2 channel scope with a current probe for this. It is a bit more advanced than listenind to the injector "click" with a long screwdriver I understand, but this way you will know what your injectors are really doing. If you use a cyl 1 triger when looking at all the injectors firing from the main power you can see what cyl(s) is your problem by following the firing order. You said you have problems when it is warm? Sounds like a closed loop problem (where you do not have fast idle). I would also check for air leaks both between the afm to tbi as well as on the manifold itself. Good luck. If you are ever in denver with her I would be happy to give her a look.

I will find an old picture or somthing to share an idea of what I am trying to explain to you.

Here is a link with pics that shows some good info http://www.linnbenton.edu/auto/scope/bteam/

 

Thanks for the info! I will definitely take a look at that.

I really need to do a compression test, to make sure it's nothing internal. But if that was the case wouldn't the engine stay running bad? It's just weird how it's ran so well for a while then it randomly crept back up. that's what makes me think the injectors are to blame, because they can stick open/shut, etc.

 

It could also be the ecu .

 

If you don't have the diag equipment, you could always swap the injectors to another cylinder and see if the problem follows them or stays with #1 and 7. I agree with last poster, could just be ecu too.

 

Is it pretty easy to remove the injectors, or is there a write up of some sort?

I've thought about the ECU, but could it cause a miss in select cylinders?

 

you can do a resistance test on all the injectors to check if they are all within range

 

So I did a compression test today.

here are the results... High numbers, but I know these gauges are not 100% accurate and you are mainly looking for consistency. I also pulled one plug at a time instead of pulling all, don't know if that would make a difference. That being said, I was very happy with the consistency of the numbers.

8 210 7 210

6 210 5 210

4 210 3 215

2 215 1 215


Has to be ECU or injectors.

 

did you get any CEL codes? I'm also curious, but how did you deduct that it was missing at cylinders 1 and 7?

If it's dirty injectors you can have them cleaned numerous ways. Off-Car cleaning is the most effective and most expensive. On-car cleaning with a solvent through the fuel line is also effective and medium expensive. Intake solvent is low to somewhat effective and not too expensive. Gas tank treatment is least expensive and least effective.

BUT if they're faulty injectors, then you have to replace or rebuild them.

Otherwise, if the problem only happens when the car warms up, then it could be your MAF sensor/O2 sensor as well. I don't think its the ecu.

 

No CEL codes.

I pulled each wire from the distributor cap one by one. All wires had a significant effect on the idle, except for 1 and 7 which had absolutely no change.

Fortunately if it is injectors, ebay has re-manufactured ones for $30 each.

Sometimes the car misses right when you fire it up, sometimes it will run great for 20 mins then start missing.

 

I pulled the ECU out today, as far as I could tell it looked fine. Didn't see any fluid or brown/yellow on the capacitators (althought they were much smaller than I thought they would be).

Hopefully it's the injectors...

Edit: ran the car for 15 min in the driveway, then drove it for 15 min. Car was not misfiring, seemed like it maybe bogged down a bit on heavy throttle. I pulled the #1 and #7 wires and this time it did affect the idle. Could they just be dirty injectors, and everytime they clog the car runs bad?

 

Drove it hard for 25-30 min and it ran great with plenty of power. Yet again once I get back home it slowly starts missing as it's sitting in the driveway. It gradually builds up and the miss is much more apparent. It's not consistent, just a random stumble. Also yet again removing #1 and #7 actually does affect the idle now. This is such a weird random misfire that comes and goes :/

 

not a great sounding clip...but if you listen closely you can hear the random miss especially towards the end.

View My Video

 

Talked to a mechanic and he said he never or rarely has heard of issues with Lexus injectors. He thinks it's an ignition issue. Is it possible the rotor or plug wires start arching gradually as it gets warm?

 

For all of you anxiously waiting on the edge of your seat, I ended up just replacing the rest of the ignition system components. I installed a new coil, plug wires, caps, and rotors ( other coil and spark plugs were new), and so far so good