Two issues on V-6; pinging under load with 91 octane and hesitating from idle (no load).

I posted in two separate existing threads and was asked to create a new thread. So here goes.

Issue 1: Pinging

"For a long time I was able to run my 2000 V6 5-spd with 87 octane year-round. No pinging.

Then I noticed occasional pinging in the summer with the air conditioning on, climbing a hill when it was pretty hot out. I started using 89 octane in the summer and it almost never pinged.

Then it got to the point where it even started pinging in the winter. For a couple of years now I've been strictly running 91 octane year-round and the problem just seems to be getting worse. It occasionally even pings in second gear now, no a/c, cool weather! I've never owned a vehicle that pinged in second gear.


Engine operating temp has not changed (according to my ultra gauge, anyway) and I have not made any mods."

Issue 2: Hesitation from idle (but great cruising power)

"My truck gets good gas mileage and cruises at highway speeds no problem. Plenty of power.

However, if I stomp on it too hard from an idle (before letting the clutch out) the engine speed takes forever to come up and if I push more than halfway from an idle I get a little pop out of the intake.

It doesn't do this when the engine is cold, perhaps because the idle is much higher."

 

I was asked to post some diagnostic information, so here goes:

Idling:


2500 RPM no load:

65 MPH on freeway:

Climbing hill in fifth gear:

 

Additional info:

• Front O2 sensor (I think it's actually called an A/F sensor in CA-emission models) was replaced in 2010 with a
  $170 Denso 234-9003 Air Fuel Ratio Sensor
  Denso 234-9003 in an attempt to fix P0171 but it didn't work.
  
• MAF sensor is original and has been cleaned several times when I had other issues like P0171 (thanks to a TRD air filter). I just cleaned it again yesterday and disconnected the battery.

 

symptoms im looking at.

• Idle - your fuel trims are cutting down a lot of fuel supply.
• 2500 no load - slightly cutting down fuel trims.
• cruisin 65 - you have higher than seen fuel trim
• under load - still increased fuel trim.

here's my list of thoughts or steps to eliminate the issue from cheapest to most expensive. i think it's one of the cheaper solutions anyways. have you changed your fuel filter recently?

1. inspect and replace all bad vacuum/intake hoses.
2. change your fuel filter.
3. clean your throttle body.
4. change MAF sensor.
5. change fuel pressure regulator. but maybe someone can chime in on testing for proper fuel pressure first?
6. change fuel pump.

 

I cleaned the throttle body yesterday, but only via the opening while working the butterfly. Seemingly no difference.

I ordered a MAF sensor earlier today because it's so easy to replace and it's only $71. The one that's in there is almost 16 years old with nearly 140K on it so I don't think it's money thrown away. If that doesn't change the numbers or drivability, I guess I'll have spare.

I may do the same thing with the fuel filter if it is getting up there in miles.

 

fuel filters should be changed frequently. like every 60k or so miles. plus they're not expensive nor difficult to install. just make sure you open your fuel cap to relieve pressure. that way the fuel doesn't squirt in your eye when you loosen it.

 

I just checked my service records (before I took over) and I can't tell if the fuel filter was ever replaced. It appears on my invoice for my 90,000 mile service, in the description, but there is no part number listed for fuel filter and associated cost.

I just skimmed through the scheduled maintenance book and I don't see it mentioned, which might be why the shop didn't do it. But I agree that I should do it.

 

TYPICAL conditions with the fuel trim:
Negative numbers are an indication of running rich. (System is trying to remove fuel)
Positive numbers are an indication of running Lean (System trying to add fuel)

You really can't get a good indication with the information on that gauge on your fuel trim at cruising speed because I can't tell what your TPS is showing, what your fluctuation in O2 data is showing, etc. Just a simple 2% change in the throttle at cruising speed can cause your fuel trim to shift to one side or the other.

Since at idle there is no change in TP position your negative fuel trim numbers could indicate an issue with air filter, air flow, MAF sensor, and fuel pressure regulator. I would inspect those and get a fuel pressure test. Plus I would inspect/change out your spark plugs and wires if they have not been done recently. Gradual wear of those items can cause similar symptoms.

These are just educated thoughts based on experience, so make sure you inspect and test.

 

Would it help to add the TPS field to that screen? I can delete the O2 #2 sensor reading since I think it only indicates the health of the cat anyway.

Air filter, plugs and wires are new as of this past summer. I am changing the MAF sensor tomorrow and will do the fuel filter as soon as I can find one (lead times are long online).

Thank you for your feedback; every little bit helps.

BTW I haven't run fuel injector cleaner in years. I used to do so every six months or so, using Techron. Not sure if it has anything to do with my current situation but I certainly don't mind running a few bottles over the next few weeks.

 

You already have two very experienced gear heads posting before me. Im just going to throw out some thoughts in reading this.

I keep looking how the LTFT is fluctuating so rapidly. I guess it doesn't matter in this case, but there is no reference to the time being taken from each reading for LTFT to swing from rich to lean.

Manifold leak comes to mind, but more specifically something affecting the FPR. Lack of idle vacuum would raise rail pressure wouldn't it?

Ported vacuum lines from throttle body for the EGR? EGR system leak....

Its not common for a electric fuel pump to die by slowing the fuel output. Its either on or off. In any case, do the fuel filter first. It should be done anyway and for $10 you can cross it off the list.

The two most valuable tools i own are my $5 multimeter and my vacuum gauge. I think your vacuum readings from various points in the intake will tell you something.

I dig that this scan gauge has a Lambda reading. Most cheap scanners dont know how to read a wideband sensor, even my old MT2500 just reads 0.5v all the time.

 

Interesting, the Lambda reading is always at 0.99x, even as the LTFT is switching form rich to lean. Maybe im reading this wrong.

 

You know I was wondering about that. I've watched that thing a lot the last couple of days and it is always super close to 1.000. I do have a few photos of readings at 1.000 or just over.

Is that the computer making perfect adjustments on the fly to A/F to settle at the sweet spot?

 

Generally, perfect 14.7:1 a/f = 1.000 Lambda. Or as @CodeSeven likes to say, Stoichiometric.

If you used a cheap Pepboys scan tool, it would read just the reference voltage or .5v for the wideband sensor. Your rear o2 sensor however is a standard 1.0v o2 sensor, it will (should) show a waveform.

The lambda reading is the ECUs internal computation of what the a/f ratio is. Why this is important is because of some states that use seasonal gasoline (California), or ethanol mix fuels. Even if the ideal a/f is not 14.7:1 for a particular fuel, the Lambda reading will still be 1.000 if the correct ratio is achieved, and the ECU can determine this number instead of just controlling the lean/rich switching.

 

I was wondering what half life 1 had to do with a scangauge.......

 

The trim numbers only go negative when I'm off the throttle. This happens 4 times while accelerating, of course, since it is a manual transmission.

I think that this is telling us that it's running too rich when I'm not stepping on the gas. At 2500 RPM no load, the numbers look pretty good. Too lean under heavy load though. But I'm very new to all of this so who knows if I have it right.

I think the MAF sensor is lying to us, but it's not telling a big enough lie to throw a code. I will find out for sure tomorrow when I replace it.

Perhaps there are multiple issues at play here.

 

Ill add, Lambda readings are inverse of a narrow band o2 sensor. Lower than 1.00 is rich, higher is lean.

It will make us feel better if you first do the fuel and air filters, just to get those out of the way. Use OEM items.

 

OEM air filter recently replaced. MAF sensor gets replaced tomorrow (genuine Toyota) before the fuel filter only because it was available on Amazon and I could have it in two days. Not so for the fuel filter which I'll have to get from a local Toyota dealer.

 

I doubt its the MAF, but i could be wrong.

Youre somewhat local. Check out BMAparts.com. Theyre in Glendale, but can get most parts same day if you call in the morning. If you dont want to drive, theyll ship most orders over $75 for free. Done business with them for nearly a decade.

I prefer the Mann brand filters. Just note they dont include the M10 washers.

 

Roger that. I'll check them out if my local dealers don't have the part. I have two pretty close to where I live.

BTW, I guess it makes sense that I have this bad hesitation problem if the ECM wants to make the mixture much leaner at idle and much richer under load. That's quite a transition to make in a split second. The engine is probably starving for fuel when I stomp on it.