This problem is a doozy! Suggestions?

[toyo]

Iv'e been working on cars for close to 30 years and this is in the top 5 in regards to puzzling.

1999 3.4 199K

This vehicle is a very good friend of my wife's and was asked to check it out for them.

Symptoms: Loss of power, gets a little better after driven about 10 miles.
Code P300, 302, 305.

I first did a good visual inspection. Coolant, oil etc all perfect.
Removed the problem cylinders spark plugs. They look very good as I just tuned it up 3 months ago.
Tested the ohms on the coils and wires, all are within spec.
Removed upper and lower intake. Tested injectors for proper ohms. All 6 read between 14.1-14.6.
Removed timing belt cover to verify the timing belt, cams and crank are all set. All good.
Replaced fuel filter.
Checked and verified proper ohms on the Crankshaft and Camshaft position sensors.
Reinstalled intake and all related components.
Cleared OBD codes.

Engine started right up but was sluggish up to 2K RPM's. If you rev it between 2-4K all is perfect. Once it hits 4100 it acts as if the fuel shutoff is coming on. A very distinct miss. The CEL started flashing as I was running it.
Shut down and rechecked codes.
I am now getting P300, 301, 302 and 303.
Restarted and physically listened to the injector poppets on each injector.

My fuel pressure gauge will not work with the banjo style that Toyota uses. I have a new one coming tomorrow that will work.

I feel it might be a fuel pressure or a catalytic converter problem. If those test out good I am at a loss. The one thing I did not check is the compression. I could kick myself for not doing this when it was torn down.

Does anybody have any other ideas or suggestions that i am not thinking of?

 

[Andy in Pa]

Was gonna say a sluggish fuel pump, or possibly a catalytic converter that is getting plugged, but it sounds like your on the right track.

A.

 

[LittleCaesar]

Have you switched the coils themselves rather than just ohming them out?

I would think if it is the cat the problem would be noticeable across the entire RPM range.

MAF, 02 sensors original?

Post the numbers when you get them.

 

[toyo]

Have you switched the coils themselves rather than just ohming them out?

I would think if it is the cat the problem would be noticeable across the entire RPM range.

MAF, 02 sensors original?

Post the numbers when you get them.

I thought about moving them around but I have no consistent codes. The only cylinders not to give me a code is 4 and 6. I'll do it for shits and see what happens.
I have not put much thought into the O2 sensors since Toyotas will almost always throw a code if faulty.
I would be surprised if the fuel pump is defective. It never has an issue starting. I can't even remember the last time I replaced a bad pump in a Toyota or Lexus. You never know though. I will be able to check it tomorrow.

I will keep you guys updated with my progress for sure. This is exactly how we all benefit from each other!

 

[Brique]

I once heard of a similar problem on a Chevy s10. After going through all kinds of diagnostics, they found that the ground on the fuel pump was iffy and so the pump was intermittently starving for power. At least i think that's how the story went. If that sounds stupid, then ignore me, just figured I'd throw it out there.

 

[IBallEngineer]

Its difficult to read your post and fully understand everything. One of the things that jumped out at me was the lack of mentioning of a new air filter. But I don't actually think that is your problem anyway.

Have you driven it with a scan tool attached to see if it is an actual misfire? I'm thinking you have a coil/wire/plug issue myself. But you CAN'T rule out the injectors. I know you said they all checked out for impedance, but that doesn't mean they aren't failing in other ways. Injectors can become plugged, and coils can overheat. This is where I'd focus, but I would definitely try to narrow the scope using a data stream scan tool, to help you isolate the failure.

The high rpm/load nature might indicate a fuel pump, but it would be lean across the board, not individualized. And the exhaust restriction would be far more evident under load than just revving the engine. Many times an exhaust restriction won't be symptomatic at all until under a load.

Here's a link with some hints, although no actual solutions.

P0300 Toyota Random Cylinder Misfire Condition OBDII Engine Light Trouble Code | Engine-Codes.com

Lastly, kick yourself again, then pull the plugs and check compression! I've been working on cars even longer than you have, and I know of no one who hasn't had to kick themselves.

:snacker:

 

[vipergrhd]

I guess i will join this game,i agree that we all have been stumped at one point and to find out the problem is in front of us the whole time.Here is my suggestion start with a fuel sample test put it in a clean glass container and let it sit,compare with a clean fuel from a gas pump if questionable.Try to get a fuel volume test do this 3 times with a measured container,maybe a 20 second crank each time.If your fuel quality and fuel volume is ok get the injectors sent out or swap with a known good one also try to swap a known good cam and crank sensor if code continue to return.that's it for now and keep us posted.

 

[toyo]

Its difficult to read your post and fully understand everything. One of the things that jumped out at me was the lack of mentioning of a new air filter. But I don't actually think that is your problem anyway.

Have you driven it with a scan tool attached to see if it is an actual misfire? I'm thinking you have a coil/wire/plug issue myself. But you CAN'T rule out the injectors. I know you said they all checked out for impedance, but that doesn't mean they aren't failing in other ways. Injectors can become plugged, and coils can overheat. This is where I'd focus, but I would definitely try to narrow the scope using a data stream scan tool, to help you isolate the failure.

The high rpm/load nature might indicate a fuel pump, but it would be lean across the board, not individualized. And the exhaust restriction would be far more evident under load than just revving the engine. Many times an exhaust restriction won't be symptomatic at all until under a load.

Here's a link with some hints, although no actual solutions.

P0300 Toyota Random Cylinder Misfire Condition OBDII Engine Light Trouble Code | Engine-Codes.com

Lastly, kick yourself again, then pull the plugs and check compression! I've been working on cars even longer than you have, and I know of no one who hasn't had to kick themselves.

:snacker:[/QUOTE

An ex-employee of mine has my Genisys scan tool. I need that one to do full blown diagnostics. I told him yesterday that if he doesn't drop it off this morning holy hell is coming!

You guys are right about the converter and the injectors. It is not giving me the usual symptoms of a faulty converter.

I sure would like to put in a new set of injectors. Wouldn't that be a nice item to cross of the list as possibly being the issue? At 200K it's not all that crazy on this particular engine.

 

[toyo]

I guess i will join this game,i agree that we all have been stumped at one point and to find out the problem is in front of us the whole time.Here is my suggestion start with a fuel sample test put it in a clean glass container and let it sit,compare with a clean fuel from a gas pump if questionable.Try to get a fuel volume test do this 3 times with a measured container,maybe a 20 second crank each time.If your fuel quality and fuel volume is ok get the injectors sent out or swap with a known good one also try to swap a known good cam and crank sensor if code continue to return.that's it for now and keep us posted.

If this problem is right in front me tools will be flying! LOL
Its funny you say that though. Yesterday I stepped back, took a deep breath and said to myself I gotta make sure it's not staring right at me and made sure I checked out the common items.
I have been maintaining this vehicle since new almost so I know what has and has not been done. That really helps big time and saves a lot of time.

 

[pdubrule]

Definitely sounds like a slipping muffler belt..... :tape2:

 

[toyo]

Ok, here's the latest.

Checked the fuel pressure. At idle with the idle sensing hose plugged it should 38 to 44. Result 46
At idle with sensing hose connected should be 33-38. Results 46. No change.

After the engine is shutdown the pressure should not be below 21 PSI for 5 minutes. Results were zero after 10 seconds.

I have no pressure with the key on. However, I could not activate the test option on the TechStream. I will do that in the morning.

From my tests of the actual fuel pump it seems to check out fine. I am going to crimp the return line in the morning to see if it has any bearing on the drop of FP when shut down.

I am thinking that several of the injectors are not holding and dumping the fuel pressure.

I feel I am at least getting close. Thoughts???

 

[LittleCaesar]

It sounds like the FPR isn't holding pressure. Pull the vacuum line off the regulator and see if you get a strong smell of gas or gas actually comes out of the line. That has been my go to test for bad FPRs for some time yet I have never heard of one going bad on a 5vz. But it doesn't mean they can't.

 

[LittleCaesar]

If the FPR is Ok, then I would suspect the pump. But I have to say I have never read the FSM to see how to test the FPR, so do such before jumping to any conclusions based on my shade tree methods.

 

[541joseph]

Injectors are the last thing I'd think. I'd check pressure regulator and pump. Just because the pump holds it at 46 doesn't mean seals aren't bad and that's not why it's losing pressure. Toyota didn't have problems with these injectors. There are a few cases where people have problems but most the time no.

 

[JBurt]

My father in laws 98 3.4 Tacoma just had an injector go bad. The only symptoms he noticed were rough running at all rpm's. It never threw any codes though.

 

[IBallEngineer]

Ok, here's the latest.

Checked the fuel pressure. At idle with the idle sensing hose plugged it should 38 to 44. Result 46
At idle with sensing hose connected should be 33-38. Results 46. No change.

After the engine is shutdown the pressure should not be below 21 PSI for 5 minutes. Results were zero after 10 seconds.

I have no pressure with the key on. However, I could not activate the test option on the TechStream. I will do that in the morning.

From my tests of the actual fuel pump it seems to check out fine. I am going to crimp the return line in the morning to see if it has any bearing on the drop of FP when shut down.

I am thinking that several of the injectors are not holding and dumping the fuel pressure.

I feel I am at least getting close. Thoughts???

Yes you are at least finding faults! Despite the naysayers, DO NOT IGNORE the fuel injectors. Don't forget you are getting individual cylinder misfire, not just a general lean condition. The obvious next step is the fuel regulator, so I think you are moving along just fine!

:couch2:

 

[Predatorhouse]

I would swap in a known good coil, look at your MAF. Those little guys can cause wacky sh_t.

 

[the great him]

I would swap in a known good coil, look at your MAF. Those little guys can cause wacky sh_t.

that does not affect fuel pressure drop though, and would also manifest in other areas if it was the faulty part.


to the OP, i know this really has no affect on the fuel pressure dropping off, but have you replaced the fuel filter recently? do you know when it was last replaced? it might be a good thing to do just cause, if its got enough miles on it...

 

[toyo]

I found it. First off the drop in FP was my fault. I did not have the banjo bolt on the fuel rail tight enough. Barely a drop but it was enough.
Now the good news! While it was idling I happen to notice the harmonic balancer seemed like it had just a little too much wobble than normal. I put my socket on it and sure enough it was too easy to loosen. Once I discovered that I knew I found the problem. I removed the crankshaft pulley and all the covers. Put crank bolt back on. Turned the crank to see where the mark on the lower timing belt gear was lining up. When I would hit the compression stroke the shaft would move but the gear would not. It would wait until the woodruff key would hit and then move. Maybe a little less than a ¼ inch. Long story short.....the crankshaft bolt backing out some caused the woodruff key to move around and creat play. Hence the erratic misfire condition and being out of time.
My oh my!

 

[TheDurk]

I found it. First off the drop in FP was my fault. I did have the banjo bolt on the fuel rail tight enough. Barely a drop would drop but it was rough.
Now the good news! While it was idling I happen to notice the harmonic balancer seemed like it had just a little too much wobble than normal. I put my socket on it and sure enough it was too easy to loosen. Once I knew that I knew I found the problem. I removed the crankshaft pulley and all the covers. Put crank bolt back on. Turned the crank to see where the mark on the lower timing belt gear was lining up. When I would hit the compression stroke the shaft would move but the gear would not. It would wait until the woodruff key would hit and then move. Maybe a little less than a ¼ inch. Long story short.....the crankshaft bolt backing out some caused the woodruff key to move around and creat play. Hence the erratic misfire condition and being out of time.
My oh my!

You're lucky you caught it early. 217 ft-lbs. (with thread-locker) is spec torque for a reason. Many with loose bolts have needed a new HB and some have fubar'ed their crank end-=basically end of motor. I've caught this condition for a few posters but I never thought this was another one.

How long since the last time that crank bolt was out? (for timing belt, water pump, whatever)