Injector Theory - what do you think?

[billsheila]

My engine woes continue, but I won't repeat the whole story. Instead I will offer up a theory on possible cause, see what you guys think.

My issue is a warm only, one time only (per start) hesitation, most notable when vehicle sits for only a short while. Lots of the usual stuff has been tried, including taking it a shop...still no fix.

My theory: I have a "leaking" injector (or two). Logic Path: When the vehicle has sat for a long while (long enough to cool right down), the fuel from the leaking injector is long gone to evap and of course it stops leaking as the fuel rail pressure drops -- so in this case I start, no issues, it runs fine. But when warm and sits for only a short while, the leaking fuel builds up and she runs like a pig causing the hesitation as she chokes on all this fuel built up. Once I burn through it, she runs reasonably well again and the problem doesn't recur on that run. On a cold start if left to idle long enough, it will sometimes start to run rough and choke up in a similar fashion (but it has to be idling for a very long time for this to happen). The above "Theory" might also explain that through all of this (at least during my ownership) the car has not thrown any codes. The reason there is no code is that the engine is just choking a bit on too much gas...the ECU compensates and works through it. No faulty equipment except the bad injector (or two).

110K, 1999 vintage. I am wondering if I should try this SEAFOAM stuff (but worry I might clog up my brand new O2 sensors)...or whether I should just dig in and remove intake manifold and all the injectors and send them away for refurbishment and testing. There is a place that does them for like $24 per injector (they send yours back to you after cleaning and testing). I also read about this MotorVac process, which sounds interesting but would be more costly that the injector job, assuming I can manage to get the intake all apart without taking it to a shop.

Any opinions on my theory would be appreciated?

 

[Stick Figure]

If you suspect the injectors are clogged and sticking slightly open i would recommend redline fuel injector cleaner. If you are going to pull them witchunter would be my recommendation.

Now with that aside. What are your fuel trims? If you are leaking gas when this happens you should see this in the o2 sensor output, and then the fuel trim. If you don't have a way to check this, then you can shut it off when it starts running rough and pull the spark plugs and check the condition of them. You should be able to tell if certain plugs are showing lean or rich. Just make sure you shut it off while its running rough to check them. Normal driving may clean them up and erase the signs you are looking for.

The other sign is if you are leaking a significant amount of fuel it won't evaporate out of the cylinder it will run down into the oil. This will do bad things to the oils lubrication properties, but will also give the oil a fuel smell.

Sorry i'm not on here enough any more to know what your other posts said so hopefully this info can help you out.

Good luck.

 

[billsheila]

Thanks for the suggestions Stick Figure. The other posts are not too exciting, just replacement of many parts, some by a shop just prior to me buying the truck (which thought they fixed it), then some more work (and parts) by me, now another trip to a pro, still no fix. As best I could, I asked the last shop for specifics about what their analyzer told them (so called "freeze frame" data) and they didn't offer anything other than "it all looked normal"...no stored codes etc etc.

I don't have an analyzer myself, but your trick of shutting her down mid-trouble and looking at the plugs is worth a try. I did try injector cleaner but not Redline, so I will try that too.

 

[brian2sun]

The MotorVac will help the injectors, but it is primarily a combustion chamber carbon cleaner and a fuel system cleaner 2nd. It will not clean the injectors as well as sending them off to Witchhunter. You issue could be a sticky valve though, and in that case the MotorVac may help significantly like it did on mine. Keep an eye on your coolant and make sure you're not loosing any because it could be leaking into your cylinder(s) via a HG leak and causing the issue as well.

 

[billsheila]

Brian2sun; You may be on to something. I got a recommendation for a local mechanic from a friend of a friend and I stopped by to see him today, small operation, word of mouth, you actually get to talk to the mechanic etc etc.

Anyway, what you describe about the head gasket he mentioned as a possibility (an unfortunate one). He suggested I carry around a good rag and a bucket and relieve the pressure from the cooling system each stop...see if it still does its trick. He said the coolant pressure will allow the seepage, then it gets burnt off. He also thought EGR valve (but he said some 4Runners don't have this). He said he could do some kind of a coolant test to confirm the situation.

 

[CO_FlyFisher]

BG44K works wonders; I'd try this over any other fuel-added cleaner (personal opinion of course). The head gasket theory is interesting, but these engines are not known for HG problems (not saying it couldn't happen though).

Have you noticed your coolant level dropping at all?

 

[brian2sun]

Brian2sun; You may be on to something. I got a recommendation for a local mechanic from a friend of a friend and I stopped by to see him today, small operation, word of mouth, you actually get to talk to the mechanic etc etc.

Anyway, what you describe about the head gasket he mentioned as a possibility (an unfortunate one). He suggested I carry around a good rag and a bucket and relieve the pressure from the cooling system each stop...see if it still does its trick. He said the coolant pressure will allow the seepage, then it gets burnt off. He also thought EGR valve (but he said some 4Runners don't have this). He said he could do some kind of a coolant test to confirm the situation.

Yes, pressure testing the cooling system is probably what he was talking about doing. If the pressure in the system goes down but no visible leaks, then it's probably going into the combustion chamber. Then he would do a compression test and maybe even a leak-down test if necessary to confirm a HG. Another self test you can do is pull all of the spark plugs out and let it sit overnight. In the morning, look down the holes with a flashlight and see if there's any coolant in there. This test won't confirm that there's not a HG leak, but if there is coolant it can confirm that there is. In other words, if you don't see coolant, nothing can be ruled out, but if you do then you know for sure it's a HG.

BG44K works wonders; I'd try this over any other fuel-added cleaner (personal opinion of course). The head gasket theory is interesting, but these engines are not known for HG problems (not saying it couldn't happen though).

Have you noticed your coolant level dropping at all?

Hopefully this is not the issue because HGs aren't cheap labor, but you never know - it can happen to any engine no matter what it's reputation is, especially if the cooling system has ever been neglected or if the truck has ever overheated.

 

[billsheila]

I can't say on the coolant level. Coolant looks clean (red in color). I will keep an eye on the level and see if it starts to consume any coolant. On the issue of engine reputation, was it the 4th gen engines that had a problem with head gaskets? I searched that and it seems there was a recall or something.

 

[brian2sun]

The 3.0 V6 in the 2nd gens had the HG recall. Those engines are just a bad design.