Toyota V8 no runny, the hell you say!

lendaddy · 07-31-2006, 11:35 AM

My Tundra suddenly went domestic on me Friday

2000 Tundra 4.7L V8

It refuses to stay running. It starts every time, revs to 1000RPMs then begins dieing. Sometimes it will catch itself at 150-200 RPMs and rev back to 1000RPMs before finally stalling out. This ususally lasts 3-5 seconds.

If I rev it to 3000+RPM's I can keep it running, but only if I pump the throttle to rev it between 3k and whatever RPMs. If I try to just hold it at 3k+ it also dies slowly.

This is a drive by wire setup and all of those components check out. We tested the MAF as well.

It acts like a GIANT vac leak, but we cannot find one.

The fact that I can rev it and keep it running makes me think it NOT a fuel supply issue.

We ran a OBDII and the only code was for a heated oxygen sensor, which wouldn't cause this (I believe)
Any ideas?

singpilot · 07-31-2006, 11:38 AM

You mean too much air and not enough fuel? Could still be a dying fuel pump.

lendaddy · 07-31-2006, 11:42 AM

Quote:

Originally posted by singpilot
You mean too much air and not enough fuel? Could still be a dying fuel pump.

??? Not sure what you mean. The fact that I can rev it, bumping between 3.5K and 4.5k RPM's indefinitely without stalling makes me think it has adequate fuel supply to sustain idle. My theory anyway.

Tim Hancock · 07-31-2006, 11:46 AM

Len, I will trade you an Audi for it!

Sorry, no clue on how to attack your problem.

Maybe try choking off the intake to see if less air helps which might point to a fuel issue as opposed to an electrical issue?

lendaddy · 07-31-2006, 11:56 AM

Quote:

Originally posted by Tim Hancock
Len, I will trade you an Audi for it!

Sorry, no clue on how to attack your problem.

Maybe try choking off the intake to see if less air helps which might point to a fuel issue as opposed to an electrical issue?

Deal! This truck has a salvage title and I only paid $6k for it

But anyway, it really has me baffled. I think I'll take tonight off and mess with it more tomorrow.

kang · 07-31-2006, 11:57 AM

Most modern cars have some sort of idle control valve, or idle stabilizing valve, that allows a small amount of idle air to bypass the throttle plate. Before modern computer controlled cars, idle was controlled by having the throttle plate open a crack. Now, the throttle plate closes completely, and this idle valve, which is controlled by the computer, is what allows the idle air to get into the engine. I’m sure this engine must have one as well. It is common for these valves to get gummed up with carbon and get sticky, or stuck closed, or operate slowly. I have two cars in my garage that have this problem. The symptoms are exactly as you describe. The simple solution is to gain access to the valve and clean it out with carb cleaner or brake cleaner (no residue).

Look near your throttle body for some way for air to get past the throttle plate. You should be able to find the idle valve. It will have some wires attached, which the computer uses to open and close it. The whole thing, including the air inlet (which will typically take filtered air at a point past the mass air flow sensor, the valve, and the route past the throttle plate, might be embedded into the throttle body itself.

Good luck. You could also try this forum, or one of the other forums on this board, for help. That engine is used in a number of Toyota models, so maybe find the most active board they have and ask there. http://www.yotatech.com/forumdisplay.php?f=28

pwd72s · 07-31-2006, 11:58 AM

Could very well be a sensor of some kind...

tobster1911 · 07-31-2006, 12:13 PM

Quote:

Originally posted by kang
Most modern cars have some sort of idle control valve, or idle stabilizing valve, that allows a small amount of idle air to bypass the throttle plate.

My first thought too. IIRC, the 944 has this as well. The only problem is why it would continue to die even with throttle applied but below the 3k rpm. Wild hare-brained thought but, what about a plugged cat? The reason I ask is because it restarts fine, leading me to question exhaust flow. If the O2 is bad maybe there is more wrong in that direction.

lendaddy · 07-31-2006, 12:13 PM

Thanks Kang, this does have an idle control setup, but it appears to be integrated into the throttle body/fly by wire setup. Like I said, it's fly by wire, so it opens and closes via a motor on the shaft and that apears to work fine and tests out. Also, there is a "limp mode" where you discontect the elec. connection to the assembly and it locks the butterfly to the shaft for true mechanical operation. The motor does NOT run any different in this mode. it's just weird.

lendaddy · 07-31-2006, 12:19 PM

In other words if you hold the butterfly at X%(eliminating the idle control"circuit" from use).... you would expect the engine to run at a certain freewheeling RPM but it doesn't, it just slowly dies.

turbo6bar · 07-31-2006, 12:48 PM

perhaps operating the throttle tells the ECU to give acceleration enrichment. When the throttle hits steady state, it relies on flow data from the MAF. Intake leak would be my first check, or chunk the engine and get a junkyard 350. just kidding.

check fuel filter and fuel pressure.

tobster1911 · 07-31-2006, 01:00 PM

Quote:

Originally posted by lendaddy
...it just slowly dies.

Have you ever put a potato in a tailpipe as a prank? It will do this as the back-pressure/CO2 increases. When shut off it will leak down and the engine will restart. I still hold to checking the exhaust. Interested to hear what the result will be.

sammyg2 · 07-31-2006, 02:52 PM

My tundra runs like a top, no problems at all. Except for that complete transmission replacement at 30k, or course.
Sorry, no help here.

john70t · 07-31-2006, 03:25 PM

I second tobster. The mostly blocked cat will allow the pipe to fill up, then backpressure will dirty up the O2 and finally get back to the head. Putting your hand over the tip and smelling it might indicate at lot.

Another wild guess for the vacuum leak theory is the brake booster has an internal tear in it, or the EGR is sticking open. Try taking off and blocking all the unessesary hoses.

kang · 07-31-2006, 03:49 PM

Try the forum I mentioned above.

lendaddy · 07-31-2006, 03:50 PM

Quote:

Originally posted by kang
Try the forum I mentioned above.

I have been, not much luck yet but thanks.

RichMink76 · 08-01-2006, 10:22 AM

A co-worker had problems with his 2000 Tundra recently. Turned out to be fuel injectors.

Rich

lendaddy · 08-01-2006, 10:23 AM

I'm actually thinking fuel pump or the pressure control system. It would explain the startup and acceleration supply, but none otherwise. I think...????

onewhippedpuppy · 08-01-2006, 10:43 AM

Usually it's easy to check pressure at the rail, maybe give that a shot to eliminate fuel supply as a question. Ever hear a rattling sound in the cat area? Often times the core stuff (tech jargon) starts to come apart when they're shot, and it sounds like marbles rolling around in the cat. Try banging on it with your hand. Not the only way they wear out, just one of them. I'd be suspicious because of the O2 sensor code, very well could be something else causing it to throw the code. Maybe try pulling the pre-cat sensor and see if it makes a difference with the reduced backpressure?

turbo6bar · 08-01-2006, 10:44 AM

Measured fuel pressure?