Coolant valley repair + new plugs - now low power (2 Viewers)

[oilfield75]

2010 GX460 with ~225k miles, owned 10 years and it's been solid. Historically, the dealer has done any work beyond basic maintenance and I've been happy with them, but as I've modified the vehicle over the years I'm transitioning to a local Lexus/Toyota specialist. This shop repaired a newly discovered coolant valley leak, and they asked if I wanted to replace spark plugs while they had everything off the top. They were last replaced ~120k so I said sure.

Upon receiving the vehicle I immediately noticed a significant reduction in power. It was erratic and quickly got progressively worse. I'd be driving with limp-mode level of power (which I experienced with the secondary air injection issue years prior), and I could be pretty deep on the throttle when it would return to full power and lurch forward. Scary. No check engine or any other dash light, no codes. I returned it to the shop that did the work, and they drove it and acknowledged/replicated the problem. They were puzzled by lack of codes, checked plugs and connections, didn't replace anything. They ended up disconnecting the battery and "touching the clamps together to reset the system and drain capacitors in the ECU" (their words, not mine). I'm dubious of the explanation but they didn't charge anything and it seemed fine afterwards. Maaaaybe it was still a little down on power, but I convinced myself that it was in my mind because it was much improved and generally downshifted about when I expected it to when I got on the gas.

But now after having driven it for a while, I believe it is slowly returning to a "gutless" state, and the mileage is definitely worsened. I've been lifted on 33s for a while, and I'm used to getting 13 mpg on a pure city/surface street commute, and 17 on the highway (dash indicated, not corrected). Now I'm getting 11.5-12 and 14.5-15 highway with more downshifting. And it's been a while so I'm pretty sure about it.

My instinct says plugs/coils. Any other possibilities to consider or eliminate? Any troubleshooting I can do with basic tools and multimeter? I've lost confidence in the shop I've been using so if the next step is definitively 'check the plugs and replace the coils' I'll do that myself. Otherwise if it's open ended and could be several things, I suspect I will take it to the dealer and tell them the history. I appreciate any insight you guys can offer, so I can get back to just posting pics of cool places I've driven through.

Thanks!

 

[jakemccurdy]

That sucks and sorry you didn’t get any help here after 10 days. Definitely sounds like a fire or fuel issue. Maybe they didn’t use properly gapped plugs. I’ve only done plugs on my 3rd gen, I had Toyota do my GX. What plugs did they put on the invoice? I assume they’re supposed to be iridium but not sure the oem brand. It was Denso on my 3rd gen.

Let us know if you’ve made any progress.

@Acrad you got any insight here?

 

[jakemccurdy]

And 14 freeway is way low. I get 14 mixed on 275/65’s and just saw 22mpg this afternoon after getting the fuel injectors cleaned (just the drip line fuel service) from my shop and taking it for a spin on the freeway.

 

[Acrad]

I wonder if something up with knock and/or O2 sensors?

I’m not sure how far out of tolerance those have to go to spark a CEL versus runtime logging data that would indicate degraded

No expert but would probably need a Techstream setup or equivalent data logging to pin down cause

I mentioned knock sensor since those connectors can definitely be impacted with coolant valley repair or exposure to coolant if left unrepaired for an extended period of time

 

[jakemccurdy]

No expert but would probably need a Techstream setup or equivalent data logging to pin down cause

@oilfield75 if you want to give techstream a try for diagnostics here’s a stupid video I made on how to get setup. Works well with 2010’s

Toyota Techstream Software - Overview and Install

 

[oilfield75]

Thank you both for the comments. I haven't done anything yet. I have a v short commute and otherwise minimize the miles and use wife's or daughter's vehicles for errands, since I have that luxury until I have time to break out tools.

I plan to pull the plugs and confirm brand and gaps this weekend. I just have, like, a foggy memory of anecdotal stories where new spark plugs expose already-degrading coils somehow. So was curious if anyone could speak to whether I could test them. Probably bs.

I am intrigued and am going to research the knock sensor idea... That something might be retarding my timing has a real ring of truth.

 

[oilfield75]

Will techstream allow me to see if the knock sensor is retarding the timing? The more I think about it the more I think this is the first path to go down.

I enjoy working on cars and exploring shallow rabbit holes but.. my time is *kinda* limited and I have had only good experiences the local dealer (Sewell in DFW).

 

[ericm979]

Incorrect gaps on the plugs would cause either earlier fouling or slightly poorer running depending on if the gaps were too wide or too narrow. But they'd have to be pretty far out, and these days most plugs come either dead nuts on or close. Plugs far to hot could cause detonation (but the ECU will pull timing/add fuel to try to suppress it). Too cold and they'll foul eventually.

Sure pull a plug and check it. But this sounds more like a damaged sensor or damaged wiring to a sensor than the wrong plugs or wrong gaps. You'd think that would light the CEL though. I'd scan it first.

 

[Acrad]

Techstream and OBD Link/Fusion can show you sensor parameters

I’d suggest pulling down the FSM versions from this thread for troubleshooting…. There are a few here

GX 460 Manuals

This post will hopefully be a permanent thread along with the "150 Series Pic Thread" thread as a easy to find resources for all types of GX 460 manuals. Suggested manuals/material to post being: Factory Service Manual (FSM) Owner Manuals (for each year) Wiring diagrams Anything that may relate...

forum.ih8mud.com

 

[jakemccurdy]

Will techstream allow me to see if the knock sensor is retarding the timing? The more I think about it the more I think this is the first path to go down.

I enjoy working on cars and exploring shallow rabbit holes but.. my time is *kinda* limited and I have had only good experiences the local dealer (Sewell in DFW).

I haven’t used mine for diagnostics, just settings but it should. Its like $40 for a usb adapter so it’s a low risk venture. You could also try a bluetooth code reader. Some codes don’t trigger CEL but show up with a reader. Helps keep the rent-a-wrencher honest.

 

[r2m]

And 14 freeway is way low. I get 14 mixed on 275/65’s and just saw 22mpg this afternoon after getting the fuel injectors cleaned (just the drip line fuel service) from my shop and taking it for a spin on the freeway.

You must be coasting downhill with a tail wind.

 

[jakemccurdy]

You must be coasting downhill with a tail wind.

Don't forget drafting behind a semi truck ; )

It was only 15 miles so I might just be hoping that $150 fuel service wasn't a total waste of money. Back to 15ish with mixed driving but haven't gone far. Will have to put a few hundred miles on to see where it's really at.