Acceleration hesitation (1 Viewer)

[450LX]

I have a 224K 1997 450LX with an acceleration hesitation. The truck runs and idles fine and is throwing NO codes. The problem does not exist when the truck is cold. When the truck is warmed up and I’m starting EASY from a dead stop it will hesitate between 1400 -2000 RPM in every gear. If I am hard on the throttle it will not hesitate. Also, every once in awhile if I have the ac on and I’m idling, and the truck is warm, it will miss once periodically.
I have done a ton of reading and I have read everything from cleaning the throttle body and EGR, replacing the computer, and checking wires by the EGR and by the glove box. I have checked the wires by the EGR and the wires are fine and not charred. I did retape everything with some reflective heat tape and zip tied them away from the EGR pipe. The ECM wires by the glove box are fine and I have padded the bar where they tend to rub.
I really don’t want to start throwing money at this problem until I know what is wrong. Anybody have these same symptoms and fixed it? Thanks!

 

[ppc]

I would check the fuel pump and related circuitry. Our trucks use a two speed fuel pump circuit. Under light loads a relay routes the power through a resistor to the pump operating it at a lower voltage. Under higher loads and at start up the relay switches to provide full voltage to the pump. On my 94 the voltage can be monitored via a pin in the diagnostic connector. I'm not sure if that exists on the 95+ ODBII models. Monitoring the voltage when the problem is present would provide some good information. The relay can also be bypassed to provide the higher voltage continuously. If that solves the problem a new relay might be in order or the fuel pump may need replacement as it may be weak on low voltage. You should also check the electrical connections on top of the tank for corrosion.

 

[AK101]

do you have alot of hissing/vacuum when you remove the gas cap? If so it may be related to your charcoal cannister. I had hessitation issues, swapped cannister...no mas issue.

 

[450LX]

Thanks for the replies. I will check the connections at the fuel pump and let you know.

How would I go about bypassing the low voltage relay for the fuel pump?

I do have a lot of hissing unscrewing the fuel cap when I fill up every 300 miles.
Is there any way to trouble shoot this without getting a new cannister?.

 

[94SRUNNER]

You can pick up a new canister for about $40 from Autozone. There is a pretty detailed thread discussing the replacement canister. I installed one and the hissing was gone.

 

[AK101]

I used the autozone cannister on my early 80, took under 30min and I'm no mechanic. Your swap out will be much easier on your later 80 series.

I bet you get some hissing after a day of driving. Once it warms up and starts hesitating, pull over and unscrew the gas cap to release any pressure, re-tighten it and see if that hesitation goes away for a a lil while...till the vacuum builds again.

FWIW, I think I read somewhere on the forum that the vacuum created in the gas tank due to a faulty vapor cannister will try to pull the fuel back and thus cause the hesitation issues.

 

[AK101]

https://forum.ih8mud.com/80-series-tech/412261-charcoal-canister-great-option.html

 

[450LX]

Thats a great way to troubleshoot it, thank you! I will give it a try tomorrow for sure and let you know my results.

 

[AK101]

If thats the source of your problem and you end up having to swap the cannister for the autozone one, here is a video that should expain it.


http://www.youtube.com/watch?v=phYW5NCf8iI

 

[450LX]

Thanks for the link. I watched the video and undid the hoses to the canister. The problem still exists, but the hissing is gone.

Im going to look at the fuel pump connections next...

 

[450LX]

I've been doing some reading on the fuel pump relay and I don't think that is my problem. I know some of them are serviceable, but at least on my 97 the relay is sealed shut. I took the relay off and ran a wire from the battery to the fuel pump and drove around the parking lot for a minute bypassing the relay and problem is still there. I then did this test....

https://forum.ih8mud.com/80-series-tech/95052-fuel-pump-relay-resistor-60-second-test.html

The truck ran for a second and died just like the test said it would. Maybe it's still worth changing the relay, I don't know.

Is there anyone in Denver that has a Land Cruiser that wouldn't mind hanging out for an hour and swapping relays and maybe even the ecm? I live in Parker, CO.

 

[alia176]

Denver has a huge landcruiser resource so check out the club section. Lots of knowledgeable folks are in your area. Also, update your location and include some info about your ride in your signature.

 

[450LX]

That's a good idea, thank you.

 

[BILT4ME]

The one that comes to mind for me is the throttle position sensor.

 

[450LX]

Yeah I unplugged it just about an hour ago and got a cel, but it didn't stutter anymore. I think Im going to clean the throttle body and check the tps with the voltmeter.

 

[450LX]

UPDATE

I still have the shudder. I unplugged the TPS again and it is still shuddering. I took off the intake boot and noticed there was a crack in it so I have replaced it with a new one from Toyota ($110). I also sprayed some MAF cleaner into the MAF sensor. Still Shuddering. I also checked the connections to the 02 sensors and they seem fine.

I think it may be fuel related. I do have a fuel pressure tester, but I don't see any obvious way of hooking it up to the fuel rail. Any ideas?

I still need to check the connections to the fuel pump and probably replace the fuel filter and maybe the sock.

UGH!

 

[alia176]

Looks like you're eliminating possibilities one by one, good job.

Not sure if this was mentioned previously, but did you check ALL of your vacuum hoses? The ones under the intake manifold maybe rock hard with split ends.

 

[450LX]

Yeah I have not checked under the intake. I've looked at the top ones and they look okay. I'll report back.

 

[450LX]

Could a bad fusable link give me this problem?

 

[CruiseOrlando]

I had the exact same issue.

My problem? Water in the O2 sensor plug... I took them apart, cleaned them out, dried them, and then put dielectric grease in the plugs.

No more problem...