engine seems to cut power momentarily when I hit a bump

[wampa]

Hello community, first of all thank you for all as this forum has been SO helpful over the last 12 months as I've been sorting out my 2003 V8 4Runner. I got it with 254,000 miles, seller was 2nd owner since 2004, pretty minimal rust of the frame, and I got it really cheap so I've been trying to rescue it. In the meantime I've been driving the 4Runner to racetracks when we race and sleeping in it for the weekend, and I've really bonded with this thing!

A month ago, I started noticing an occasional hesitation in power as I was cruising on the highway. Almost like the engine power would cut or the transmission would slip momentarily for about 1 seconds, and do that every 5 minutes or so. Since then, I have continued driving it around town for daily errands, and I've now figured out to recreate the hesitation very consistently:
It won't happen when the truck is cold, I have to drive at least 15-20 minutes before it can happen. After that, every time I hit a bump, I seem to loose power for a second or less. The bump doesn't have to be big, even just a small shallow pothole will set it off.

I took a datalog using Torque OBDII tool, and it indeed looks like when I hit a bump, the ignition timing goes negative (values like -6, -8) for a couple seconds. Seems like this MUST be why I'm feeling the power drop momentarily! Does anybody have a lead as to what could be causing this? Thank you in advance for any insights!

 

[SurferUK]

Loose/poor connection or internal failure on a cable for something like a crank/cam position/MAF sensor? Seems like they would be used to calculate what timing is needed.

Start simple and check battery connections are corrosion-free, tight, and that the battery is healthy and sits at ~13V with the engine running. Fluctuating/erratic voltage can cause all sorts of weird issues.

Just general ideas that are easy to check.

 

[wampa]

Thank you, good ideas. I have not found any loose connections, but will keep checking around. Battery is 6 months old and very healthy, no corrosion on terminals/cables. I may give the MAF a cleaning, although the datalog shows no erratic MAF readings.

I agree that it might be a faulty sensor (MAF? knock sensor? crank/cam position sensors? Something traction-control related?) that, when bumped, is making the ECU think it needs to cut engine power momentarily. There are just a lot of possibilities and I don't want to start throwing parts at it, but maybe I have to.

I was hoping this momentary engine cut after hitting a bump was a known problem with a known cause ...

 

[Runnin on E]

it is a safety feature that cuts power when the vehicle is airborn!!!!

 

[wampa]

it is a safety feature that cuts power when the vehicle is airborn!!!!

Haha, yea to be honest I started wondering if a bad sensor could be causing traction control to come on. Does anyone know if traction control cuts timing like this when they are activated?

It doesn't look like there a "factory" way to disable traction control and/or stability control to test whether those systems are causing this (i.e. I turn off those systems and see if the engine no longer cuts when driving over bumps).

 

[Runnin on E]

There might be a way to trouble shoot that idea. If you have the locking Torsen transfer case, when engaged it turns off the VSC. The skid control button is a separate function and can only be turned off by itself not with the VSC off. You can't turn both off at the same time is what I am saying. I couldn't tell you if they are both functioning when the other is turned on/off. BUT to answer your question yes the power is cut when the vehicle senses a skid. The sensors involved in that data collection are the wheel speed sensor and the accelerometer(s). Check yer codes or record the functions using the OBDII scanner that you bought....(going to buy). Make sure the scanner can do that. Even my old scanner has a record function.

 

[wampa]

Just to close the loop on this - the occasional engine power cut appears to have been due to a dirty MAF sensor. To the naked eye the sensor looked pretty clean, but I sprayed it thoroughly with MAF cleaner and it seems to have resolved the problem.

Again, my symptoms were: engine cutting out momentarily only when thoroughly warmed up and when hitting bumps. Logging with my Torque 2 app revealed an ignition timing cut (reduced to -8 deg or so) that coincided with the momentary loss of engine power. The same data logs did NOT show any MAF irregularity. Additionally, in retrospect, my hot engine idle was also slightly hunting sometimes, up and down by about 100 rpm. Now that I cleaned the MAF, there is no more engine cut out and the idle is super smooth and solid.