What could it be? Weird "hiccup"

[muliefever]

Hey everyone,
My 1990 4runner project is coming along nicely since I purchased it two weeks ago. However, two days ago I noticed something that up to that point hadn't happened before. While driving up and over a fairly steep mountain pass, between 50-60mph I felt a hiccup in the engine. So I downshifted from 5th to 4th and pushed on, it bucked a few times and then it was gone. Yesterday I put a brand new fuel filter on it and went through the device records that the previous owner provided. Almost exactly a year ago the vehicle had the same problem, "under load the vehicle has a kick or hesitation". The mechanic shop replaced the coil, distributer and wires and apparently it fixed the issue. Now it's back. Has anyone experienced this? If so what did you do to fix it? I am going to pull plugs this afternoon.
Thanks!
As she sits today!!

 

[Bad_Vision]

Hey everyone,
My 1990 4runner project is coming along nicely since I purchased it two weeks ago. However, two days ago I noticed something that up to that point hadn't happened before. While driving up and over a fairly steep mountain pass, between 50-60mph I felt a hiccup in the engine. So I downshifted from 5th to 4th and pushed on, it bucked a few times and then it was gone. Yesterday I put a brand new fuel filter on it and went through the device records that the previous owner provided. Almost exactly a year ago the vehicle had the same problem, "under load the vehicle has a kick or hesitation". The mechanic shop replaced the coil, distributer and wires and apparently it fixed the issue. Now it's back. Has anyone experienced this? If so what did you do to fix it? I am going to pull plugs this afternoon.
Thanks!
As she sits today!!

Nice truck, most hesitation is caused in the combustion chamber by ether.
Wrong fuel mixture= injector issue
Not enough burn= coolant mixing with fuel or incomplete spark or bad fuel even.

Sounds like your on the right track with the filter now just fallow down the line to ignition components if that checks out ok might be time to test the injectors for spray pattern and flow.

Sent from my XT1635-01 using Tapatalk

 

[muliefever]

The strange thing is that under heavy acceleration there is zero hesitation. Runs great!! It's specifically l50-60mph under normal acceleration.

 

[Bad_Vision]

The strange thing is that under heavy acceleration there is zero hesitation. Runs great!! It's specifically l50-60mph under normal acceleration.

That sounds like a injector to me.
As you can see at full open all injectors spray a lot of fuel but when they are in low pressure mode the spray will be weak and if you can imagine having one cylinder not fire the same as others will make it feel like miss.
Easy to rig up for testing but depending on your mileage might not be a bad idea just to put new in if you plan to keep it.

 

[muliefever]

Oh ok thanks. I do plan on keeping it. Any injector recommendations?

 

[85straight]

You can send your injectors out for a cleaning and rebuild for about 20$ an injector. WitchHunter Performance - Injector Cleaning & Flow Testing Services is a popular choice and there are a few other companies out there. Should be much cheaper than replacing the injectors