Hello! I have an issue with my 98. When i'm accelerating up an incline at highway speeds it feels like the truck is under-powered/slipping/bogged down until i reach 3500 rpms. Then it starts to pull good and strong. I have just done the spark plugs. Spark Plug Wires, MAF, PCV valve, TPS, IAC, cleaned TB have all been done fairly recently? Would a bad coil or injector be bad under 3500 rpm then good above it?? The old spark plugs all had a whitish build up on them (not much tho.) I'd be very glad of any help. Many Thanks!
Help! 98 3.4 V6 Hesitant/surging under acceleration on incline
- Thread starter Guy Bri
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gamefreakgc
Elite Member
It's best not even to touch the TPS, which it seems you did.
The white build-up on the spark plugs is because the engine is running lean and starved for fuel. The sensors that control fuel trims are the front O2 sensor, MAF sensor, and TPS.
The white build-up on the spark plugs is because the engine is running lean and starved for fuel. The sensors that control fuel trims are the front O2 sensor, MAF sensor, and TPS.
Thanks. Is there a way to test the front 02 sensor?
BamaDrewski
New member
x2 on the 02 sensor replacement. I know from experience these 02 sensors can mimic the symptoms you are having and they rarely throw codes
Many people just change out one or the other but I would HIGHLY RECOMMEND you replace them both at the same time. Go to DENSO Auto Parts to look up what you need and then buy them from Amazon. ONLY BUY DENSO. Our rigs hate Walker and Bosch 02 sensors.
For what it is worth, I just did this on mine as preventative maintenance and my non-Cali T4R uses the same sensor fore and aft. (Denso Part # 234-4162)
Many Thanks!
I have never replaced them and i'm not sure before i owned it. Just a question....If they're bad wouldn't they be bad regardless of rpm?
gamefreakgc
Elite Member
No, because the ECU only uses the O2 sensors for closed loop operation. Once you give it heavy throttle (i.e. get it over 3500 RPM!) the ECU uses pre-set fuel trims that ignore the O2 sensor reading.
I still think it could be your TPS out of adjustment. They are super picky and extremely hard to put on correctly.
Thanks for your help. What is the correct procedure for installing the TPS
Also i purchased the 2 oxygen sensors and the front one doesn't fit? The part numbers i purchased are 234-4154 (rear) and 234-4162 (front). On the front sensor it widens right at the top and it won't fit in the hole on the exhaust? The sensor that is in there doesn't widen at the top? Be glad of any comments? The part numbers are as per the Denso website.
tystaco
New member
[MENTION=211851]Guy Bri[/MENTION] I had a similar situation happening with my 2000 Limited. I did not see codes because the check engine light had been removed... Never noticed it not turning on during start up dash lights.
My problem was solved by one of the following (can't say for sure which one) but there was an active code for the front O2 sensor, so I replaced that as well as the MAF. Before I knew i had a code I had the muffler replaced incase it had a blockage that in incline was stopping exhaust.
My bet is your O2 sensor since you have already repalced your MAF with a Toyota OEM MAF.
My problem was solved by one of the following (can't say for sure which one) but there was an active code for the front O2 sensor, so I replaced that as well as the MAF. Before I knew i had a code I had the muffler replaced incase it had a blockage that in incline was stopping exhaust.
My bet is your O2 sensor since you have already repalced your MAF with a Toyota OEM MAF.
themightygoose
New member
Why not Toyota sensors?
Why not buy genuine Toyota sensors? You know they will fit and last a long time.
Why not buy genuine Toyota sensors? You know they will fit and last a long time.
I thought Denso are the proper replacement ones??
Twheatley32
New member
You are right, I think he is saying that you have a way better chance of getting the correct one(s) from the dealership.
gamefreakgc
Elite Member
That's the hard part. If the TPS goes bad, on some years it says to just replace the entire throttle body. I don't have the FSM for the 98 year, so I cannot say. I have only successfully changed a TPS on a 1991, in which you wind up the sensor, put it on the tabs correctly so it's loaded, then using a multimeter slowly rotate it until you get the desired ohms on the sensor per the FSM. Even then, I had to turn it back a little since it was slow and didn't respond to accerleration well.
It might be worth a try of getting a throttle body off a 96-98 from a junkyard if it's cheap enough and seeing if that fixes the issue.
