HELP! Huge Mystery backfires and cuts out on acceleration after warming up.

[imagemaker]

2000 4runner 3.4. New to the page, but couldn't find an answer to my issue. So here's the issue.During a certain period, just before reaching normal operating temp, it acts like its fuel starved. Harder the pedal is pressed, the worse it gets. Clears out a bit when you lightly touch the pedal. Heres what Ive done so far... Replaced air box,(potential stripped screw on the MAS, recommended by local shop.) replaced MAS, Replaced TPS, replaced IAC, Replaced ECT, Replaced brake booster ( as per Toyota Dealer diagnosis, wrong! ) , checked vacuum lines for breaks. New plugs. Wires look good, No codes. Reset ECM,( disconnected battery for 20 minutes) Been to 4 shops, all the incorrect diagnosis. The problem is exactly the same and has not presented itself differently after each repair.
Runs fine on start up. As it approaches normal operating Temp, it will seem to lose power. If you come to a stop and accelerate it bogs down, back fires through the air box. Does the same thing if restarted after 30 minutes. When the issue occurs , if you pull over and restart the vehicle it will return to normal operation. Suggestions?

 

[SodiumFlouride]

No codes. Reset ECM,( disconnected battery for 20 minutes) ... When the issue occurs , if you pull over and restart the vehicle it will return to normal operation. Suggestions?

When you say "no codes" and at the same time you say turning off the engine resets what may be a fuel shutoff due to a misfire - I have to ask if when you say "no codes" you also mean no misfire "pending" codes.

 

[octanejunkie]

I can't see how it wouldn't throw a code with all that going on... throw a code scanner on there, it has to have something pending when all that is happening.

Also, has anyone checked the coolant temperature sensor?

 

[LittleCaesar]

I am going to ask if the timing is set correctly. The one or two time I have seen a backfire through the airbox usually is due to a lean condition.

A fuel pressure reading from cold to normal temps may be a good idea as well.

How long have you had this 4runner?

 

[JayRolla]

I also recommend some fuel pressure checks.

 

[imagemaker]

I can't see how it wouldn't throw a code with all that going on... throw a code scanner on there, it has to have something pending when all that is happening.

Also, has anyone checked the coolant temperature sensor?

Yes, Ive also placed the TPS recently, no change.

 

[imagemaker]

I am going to ask if the timing is set correctly. The one or two time I have seen a backfire through the airbox usually is due to a lean condition.

A fuel pressure reading from cold to normal temps may be a good idea as well.

How long have you had this 4runner?

I Haven't done a fuel pressure reading because I assumed it would be content vs just at that certain warm up point,
Ive owned the truck for about a year now. My Son drives it.

 

[LittleCaesar]

My two cents that along with a fuel pressure check I would also do a compression and a leak down check, to see how healthy the internals of the engine are before shooting off the parts cannon again.

 

[enapa]

Double check your spark plug wires are routed correctly. Other than that my guess is fuel injector. One of them is leaking.

 

[AntleredRuin]

I'd check fuel pressure, too.
I had the same basic symptoms when my Fuel Pressure Regulator died.

I was able to tell because the FPR started dumping fuel into my air box via the small vacuum line. Very clearly not holding pressure, and probably was sucking fuel into my air intake as well.

It was easy to start when cold, but hard to start when warm. Once warm, it could only be babied at the gas pedal. Any hard acceleration, and it would bog down/stall/misfire. Made merging into traffic downright dangerous.

I only had a CEL after one stall, then it went away after a few minutes by itself. I forget what the code was, but it pointed to either the MAF or the FPR.

I know that all FPRs don't fail the same way, but check to see if there's fuel in your air box. If so, dump it out (obviously), and order an OEM FPR.
I got a used one from eBay for about $35 shipped. I figured used is a safe bet because these parts don't fail that often. 50k+ miles later, and still working great.

 

[imagemaker]

I Just had the fuel pressure test done. 45 pounds consistently, when the issue occurs as well.
Can now make the issue occur overtime. Start the truck, let it warm up to operating temp. Shut it down and let it sit, then restart and drive, happens 100% of the time now, Backfires through the air cleaner, no power, sputters and bucks....

 

[imagemaker]

I'd check fuel pressure, too.
I had the same basic symptoms when my Fuel Pressure Regulator died.

I was able to tell because the FPR started dumping fuel into my air box via the small vacuum line. Very clearly not holding pressure, and probably was sucking fuel into my air intake as well.

No Gas in the airbox, and the fuel pressure remains constant at 45 pSi. I appreciate the input!

 

[imagemaker]

Double check your spark plug wires are routed correctly. Other than that my guess is fuel injector. One of them is leaking.

Wires are routed correctly. Checked that earlier.
If it was an injector issue wouldn't it be consistent instead of for just a minute or two before normal running temp?

 

[imagemaker]

My two cents that along with a fuel pressure check I would also do a compression and a leak down check, to see how healthy the internals of the engine are before shooting off the parts cannon again.

Thanks for the input. Fuel pressure check done, and performing at 45 psi, even when the issue is occurring. FYI, the issue seems to be exasporated when the AC is on.

 

[LittleCaesar]

Then you can rule out fuel. I take it you didn't smell any gas. I'd even guess that the ignition side is good as well.

What is battery voltage as well as the alternator output? I'd still say a compression and leak down test are on the docket.

 

[imagemaker]

Then you can rule out fuel. I take it you didn't smell any gas. I'd even guess that the ignition side is good as well.

What is battery voltage as well as the alternator output? I'd still say a compression and leak down test are on the docket.

Battery is fine, 12.7 volts, I have a Sub with a voltage regulator so I can also see the alternator working fine. No issues at all with starting.
I'll consider the compression test, but seems an unlikely path because the issue goes away when the truck is restarted

 

[enapa]

Wires are routed correctly. Checked that earlier.
If it was an injector issue wouldn't it be consistent instead of for just a minute or two before normal running temp?

How many miles?

 

[deep994rnr]

I own a 1999 4RNR V6 Limited with 129K miles that has very similar behavior.
Did you ever find a solution to your problem ?
When my engine is cold or hot it starts and runs fine. When engine is hot and then switched off for 30-60 minutes it starts up fine and runs OK for a few yards. Then as one steps on the gas there is no acceleration whatsoever. Instead it sounds like muted backfiring and there is a total lack of power. Then after about 30 seconds of this it starts to accelerate normally and runs fine. The only code that has come up is P0440.
I have replaced the Gas tank cap, ECT sensor, both O2 sensors, Ignition coil packs and wiring, MAF sensor, Vacuum switching valve, Fuel pressure regulator and most recently the EVAP canister assembly.
Any suggestions would be greatly appreciated.

 

[phattyduck]

I own a 1999 4RNR V6 Limited with 129K miles that has very similar behavior.
Did you ever find a solution to your problem ?
When my engine is cold or hot it starts and runs fine. When engine is hot and then switched off for 30-60 minutes it starts up fine and runs OK for a few yards. Then as one steps on the gas there is no acceleration whatsoever. Instead it sounds like muted backfiring and there is a total lack of power. Then after about 30 seconds of this it starts to accelerate normally and runs fine. The only code that has come up is P0440.
I have replaced the Gas tank cap, ECT sensor, both O2 sensors, Ignition coil packs and wiring, MAF sensor, Vacuum switching valve, Fuel pressure regulator and most recently the EVAP canister assembly.
Any suggestions would be greatly appreciated.

Hopefully you saved all those 'old' parts, just in case.

Your symptoms sounds like very bad misfiring while things are running poorly. Since it runs well most of the time, I'd assume most of the components are working well that you replaced...

Get an OBD-II reader that can display live data. Have it show short term and long term fuel trims along with open/closed loop.

When it is running poorly, check if it is open or closed loop.

When it is running well, check to make sure fuel trims are within a range of +/-5%

You need DATA to figure out the problem - firing the parts cannon is either really expensive (OEM parts) or problematic (most aftermarket parts).

-Charlie

 

[TheSkipper]

Last time I had this happen I slipped a tooth on the timing belt. Super hard to diagnose. So few people will give the right diagnosis. I spent forever chasing that one.
Buy me a beer if I’m right….