'00 Ranger 3.0 - Hesitation/buck at freeway speeds

[fast240z]

I bought a used 2000 Ranger 3.0L 4x4 5 spd MT and have been trying to get her into good working order. When I bought the truck, it was throwing a CEL for misfire which ended up being due to bad valve seats in the cylinder heads (proven by compression test). Two new heads later and the truck runs way better and no longer throws a CEL, but still has a slight hesitation when accelerating from 3000-4000 and will jerk/buck when accelerating.

Truck idles fine, sits around 750-1000 rpm. Occasional rough stumble during idle but pretty rare.

Parts I've replaced so far:
new heads
new camshaft synchronizer and camshaft sync sensor
new wires
new plugs
new coil pack - this fixed 95% of the bucking issue

Everything else on the truck is stock.

Any other ideas? I have an OBD2 scanner and can pull PIDs if someone can recommend something to check.

Thanks!

 

[RonD]

I would change fuel filter if you haven't, $15, and needs to be done every 5 years or so

Clean MAF sensor, every year

Look at the TPS(throttle position sensor) data with your scanner, should be nice STEADY % or voltage, whichever you are viewing

While a TPS doesn't wear out that often it is a Variable resistor, like a volume control or light dimmer, so "can" get "dead spots"

TPS gets 5volts from computer with key on
Sends back under 1volt throttle closed, .69-.99v is spec
As throttle opens voltage goes up, at WOT(wide open) it should be 4.5-4.9v, above 4.49v is spec

IF................there was a dead spot then at certain RPMs(throttle positions) the engine could buck IF computer thinks you took your foot OFF the gas pedal(voltage drop), so symptom would be like YOU were feathering gas pedal, i.e. bucking

Long shot but not no shot, lol.

 

[91stranger]

What does it do when you go from 0-70 pedal to the metal? Does it stick buck/hesitate? Like RonD said, start with some of the basics like cleaning sensors and the fuel filter. I would give the throttle body a good cleaning as well as the IAC, MAF sensor, and anything else that looks dirty or corrosive. I would check the fuel pressure too. You didn't say how many miles this truck has but being almost 20 years old I would keep an eye on the fuel pump. I could see the fuel pump doing this if it is starting to go bad. When idling can you give it full throttle and it get right up to the rev limiter? That occasional rough stumble you mention just keeps making me think fuel pump.

 

[fast240z]

It's been a while since I got a chance to reply. I replaced the IAC valve as it was causing high idle, and replaced the TPS as it wasn't allowing full throttle voltage output. The truck revs to redline fine at idle, and will row through the gears under WOT from dead stop without bucking. The issue does seem to be worse when the truck is cold and minimizes greatly when the truck warms up.

 

[91stranger]

I would replace the ECT sensor and clean the MAF sensor really good with a MAF sensor safe cleaner. New sensor and a can of cleaner will set you back about $15 at any parts store. Those ECT sensors don't sound like they would be a likely culprit but you say it does it when it is cold so if this sensor is bad then it would causing funny/erratic idling. They take about 5 minutes to change and that includes getting the tools and cleaning up the mess lol. Lot easier than a fuel pump.

 

[Bill]

I diagnosed a random bucking problem that occurs mostly on the freeway, but has happened a few times during a high idle. While monitoring the OBD II statistics I noticed the MAF was reading 0, which it wasn't doing the other day when I was trying to figure out the problem. Wiggling the wires at the connector didn't make a difference. The MAF came back online, so I think it may be failing. So, I ordered one from Rockauto. Estimated delivery time is a full week, so that means it's coming from a warehouse on the East Coast. At the rate things have been going this winter I'm expecting weather to delay shipping. So, I think I'll have it in about two weeks.

 

[Burnsy]

Get your MAF yet?