P0300 P0303 P0171 - diagnosing

Hi folks! Long-time forum stalker here.

I am trying to diagnose some engine codes on my 1st gen Taco. I've been messing with this problem for over two years. Hoping to glean some wisdom from some of you folks who are smarter than me and fix it once and for all.

These are common issues, and I've found related threads on this forum. I've read those threads and have been trying some of the solutions found in them with no luck so far.

This 2001 truck is a daily driver. 3.4L engine. It does not sit long without being driven. It has a factory installed TRD supercharger and aftermarket K&N air filter. The supercharger was rebuilt 2 years ago. Truck has 236,000 miles.

Current Engine Codes:

• P0300 - Random/Multiple Cylinder Misfire Detected
• P0303 - Cylinder 3 Misfire Detected
• P0171 - System Too Lean

Symptoms (may not be related to the codes):

• When starting the truck cold (sitting more than a couple hours), the truck will run rough for about 60 seconds. Very rough sometimes. Then it smooths out completely and drives normally. Sometimes on cold mornings I'll see what looks like smoke from the tailpipe to me. Doesn't look like vapor.
• No engine roughness while driving.
• I've noticed a loss of power at high RPM before a shift, like under heavy acceleration uphill, etc.
• Antifreeze seems to be be leaving the system somehow. I keep topping it off. I hear gurgling in the heater from inside the cab when I run the heat or A/C, which indicates some loss of coolant and air in the system. When I replace missing coolant, that sound goes away. I have never seen any indication of an overheat. Gauge on the dash is always pegged right in the middle of Cold and Hot. But the previous owner could have overheated it I suppose, and cracked the head or block or head gasket.
• Once I did not drive the truck for many days. Nearly a week. And it was COLD. When I started it up, it ran super rough for much longer than usual. Almost 2-3 minutes, I would guess. And there was also some white smoke coming out of the tailpipe. Or at least it seemed like white smoke. After 2-3 minutes, the engine smoothed out again and ran fine thereafter.
• Sometimes after starting the truck it will smell super-rich, the strong smell of gasoline. It goes away after a few minutes.

Things I have tried so far:

• I have replaced the MAF sensor twice. Currently it's about 6 months old, and I'm going to go and clean it again. It's under warranty, and my buddy at the parts place will replace it for me no problem if I ask. But both times I replaced it, that did not solve my issue.
• I bought new coils/wires and replaced all spark plugs. I used NGK BKR5RGP's. Not positive if that is the best option for plugs. Open to suggestions. Plugs have 6 months on them now and they look okay to me. I'll post a pic.
• I removed the K&N air filter completely, and cleaned it thoroughly and air dried it in the sun for several hours. I cleaned the MAF sensor and reset the codes, then drove around without the air filter on to see if oil from the air filter was perhaps coating the MAF and messing up the sensor.
• I have checked for vacuum leaks. I did find one right at the MAF sensor, which I was able to eliminate with some silicone sealant around the threads where it connects to the air intake pipe. Eliminating that leak hasn't solved the problem. Yes, I do reset the codes after I try a fix.
• Run SEVERAL bottles of fuel injector / fuel system cleaners through. I tried every brand out there. Started with a full tank and dumped a bottle in. Reset codes. When code came back, I tried a different brand (or another bottle).
• The loss of coolant combined with the rough running on start up has made me think I have a blown head gasket, or possibly a cracked head. So I decided to do both a compression test and a leak down test. The dry compression test was performed on a warm engine.
  • DRY COMPRESSION TEST RESULTS
    Cylinder 5 - 138 PSI
    Cylinder 3 - 146 PSI
    Cylinder 1 - 130 PSI
    Cylinder 6 - 133 PSI
    Cylinder 4 - 130 PSI
    Cylinder 2 - 131 PSI
    I think you would agree these are good results for a dry compression test (I say dry because I did not squirt any oil into the cylinder before taking the readings).
  • LEAK DOWN TEST RESULTS
    Cylinder 5 - 15 PSI
    Cylinder 3 - 15.5 PSI
    Cylinder 1 - 15.5 PSI
    Cylinder 6 - 15 PSI
    Cylinder 4 - 15 PSI
    Cylinder 2 - 15 PSI
    For the test, the rad cap, oil dipstick were removed and the and air filter disconnected from the throttle body.
    
    For ALL cylinders, no bubbles/air seen escaping from coolant, nor oil dipstick. I did hear a very faint sound from the tailpipe on all cylinder tests, and I think that's normal. Not hearing or seeing any air escaping from the coolant via the radiator cap opening really confused me. I thought for sure I have a blown head gasket, but if I did, surely I would see bubbles coming from the radiator cap opening on at least 1-2 cylinders.
    
    

Since the compression test looks good and the leak down test didn't indicate a blown head gasket, I can only assume that the coolant disappearing from the system has to be from something else. Strangely, there are no leaks on the driveway. None at all.

I would assume you can have a leak down test not show air from the coolant (radiator cap opening) and still have coolant leak into your cylinders from somewhere else... the air was escaping at 15PSI from all cylinders evenly, which I would expect on a perfectly healthy engine, so that is strange to me. I expected to see at least one cylinder with a higher reading than the others. I keep coming back to thinking there is coolant leaking slowly into the cylinders and that's why it runs rough on startup.

Lean code P0171 could be caused by fuel starvation. That could then cause the P0300 and P0303 codes. So I'm going to replace the fuel filter today. The fuel pump could be next. I'm going to figure out how to test the output pressure from that pump and do that ASAP. Could also be clogged injectors. I have no idea (yet) how to test the fuel system, but that needs to be checked to rule it out.

If any of you have other thoughts on what I could try, I'm eager for any advice. Super stumped on this one. Hoping the fuel system is the issue, because filter and/or pump would be a fairly simple job.

The PCV valve looks okay to me, but I suppose I could replace that too.

Happy Easter! Thanks for reading!

 

I stopped reading about a third of the way through when you started saying there is loss of coolant but the leakdown and compression test showed fine.

This sounds very similar to what I had with my 1st gen when I bought it. Heads are cracked and are letting coolant into the exhaust and into the cylinders. That's why when you start it up it's super rough until the spark plugs heat up and the coolant burns off through the exhaust system in that sweet smelling white cloud.

Good luck.

 

The only way to confirm that would be to pull both heads and inspect for cracks. Got my work cut out for me!

Thanks for confirming my suspicion!

This video is really going to come in helpful:

 

Yep, hopefully your work is "rewarded" by finding the issues.

While you're in there and have the engine apart you may want to start thinking about supercharger upgrades

 

What kind of supercharger upgrades ??

 

It depends on what supercharger you have... the older "gray" one or the newer black one?

 

@1997tacomav6 will have some ideas for sure

 

Definitely.

https://www.tacomaworld.com/threads/trd-supercharger-power-mods-and-tricks.628051/
https://www.tacomaworld.com/threads...alled-silver-bullet-tune-snpspeed-com.722842/

and many more..

 

Out of curiosity- are you running single electrode spark plugs for a specific reason?

 

Only because I was too stupid to notice the blue sticker right on the engine shroud telling me to use duals! LOL

 

The black one

 

Easy way to check/verify if coolant is entering a cylinder is to pull the plugs and use a cooling sytem tester to put pressure on the cooling system, leave it sit for an hour or so with pressure then come back and look if any cylinders have coolant sitting in them.

 

At this point going forward I would not suggest anyone buying the 1st gen superchargers unless you see it running and there are no issues with the snout.
You can no longer buy case parts for the 1st gen. IF you ended up with a used supercharger and the case of the snout was bad from a spun bearing or a bad shaft your not going to find parts to fit it and the used snouts have all dried up or if needed a bypass cap.
Buying a 1st gen is a pretty big gamble now unless you can return it if there is a problem or the seller has history on it
FYI

 

I was going to say that maybe your upstream O2 sensor was dirty/clogged from the KN filter not really filtering particles.. but then I started wondering about the question of the disappearing coolant. It's going somewhere alright, and most likely a small leak within the engine. You can maybe try removing the skid plates and letting it sit after some use, to see if the coolant leak is external.. but I don't think it'll do much considering that the truck blows white smoke in the few moments after starting up

 

This is a great idea. I hadn't even considered this. I have a professional cooling system toolkit and it could accomplish this. I'll try it and post back! Thanks!

 

Had a similar problem, misfires then too rich. replaced injectors with parts store remans. fixed the misfire but a code came later, too rich. Just ordered and installed injectors from motorwestperformance. Truck never ran this good while I owned it.

 

This exact thing also happened to a 98 Chevrolet C1500 I just fixed up. It had been running a KN filter that had not been cleaned in years, so the upstream O2 sensor was very clogged and dirty. It had a misfire on cylinder 5, and has been running like a champ since the injectors were replaced

 

Same on my ‘99 with 3.4. Was running rough with misfire codes 0300, 0301, 0303, and occasionally 0306. Bought new injectors from MotorWest and problem solved

 

Thought I would post a quick update.

I just left town for 8 days for work and got back last night. Before I left, I had gone to O'Reilly to get a tool and I just happened upon a bottle of K-Seal Ultimate. I read the label and figured what the hell - for $25 it's worth a shot, and I can get my money back if it doesn't work. I bought it and didn't have a chance to use it before I had to leave town for work, so it just sat in the Taco.

This morning, I shook the K-Seal bottle hard for a bit and then drained enough coolant from the rad to pour the bottle in. The engine was stone cold; the Taco hadn't been run for 8 days. I started the engine. It choked and sputtered, and ran super rough, then died. White smoke was billowing from the tailpipe. I started it again and it struggled but finally got running enough to idle, while it continued to push white smoke for maybe 90 seconds.

I let it idle for 10-12 minutes, with the A/C on max cold, full blast. I had my scanner hooked up to the OBD port and could still see the cylinder misfire codes P0300 and P0303.

Then, it started running really, really well. Idling better than it normally does, actually. And the two misfire codes cleared themselves!

I am not going to get my hopes up yet, I'll check for the codes again tomorrow. But for now, it would seem that the K-Seal has perhaps sealed the leak and solved the misfire codes.

There is still the lean code P0171. I replaced the fuel filter, cleared the code manually, and drove it. The code returned 20 min later, so I think I'm going to pull the injectors and send them to motor west performance be cleaned. I think I'll also replace the upstream O2 sensor if I can figure out where it is.

Other possible parts that I think could cause "system too lean" could be a failing fuel pump, or MAF sensor, which I have replaced twice now. Oil from the K&N filter on the MAF sensor might cause it to run lean, perhaps. I could try cleaning the MAF and removing the K&N to see if that helps.

I checked for vacuum leaks, I don't see any.

I'm gonna solve this or die tryin.

 

Fwiw,
I also had to replace the fuel pressure regulator when I did my injectors. The FPR was no longer working. It was a fairly cheap and easy part to replace when you are already doing your injectors. Don’t be like me and install all new injectors and button everything back up, only to pull it all back apart just to replace the FPR. I’d recommend doing that while you do you injectors.