Sputtering, loss of power - Case of Beer for the person solves! :) (1 Viewer)

[twitchfury]

Hey guys! Need your help.

1993 FJZ80 - 275k Miles
Until recently no issues until about a month ago, truck started rough idle, loss of power, and sputtering while cruising. After reading through the forum, I thoroughly cleaned the TB and MAF sensor, cleaned EGR, put it all back together, and checked and inspected for vacuum leaks. None found. I also changed the fuel strainer. There was no improvement. Not having a lot of free time right now and not sure where to go with it next, rather than throw random parts at it, I took it to a mechanic.

Mechanic changed all the spark plugs, (said the back three looked bad and wet) and they also took apart the throttle body for another thorough cleaning, replaced the TB gasket which I had apparently bent, and replaced the water pump which was unrelated. Truck idled MUCH smoother, symptoms improved a bit. BUT took it out on the highway and it sputters/misses (not sure which) around 60-65MPH/sustained 2200-2500 RPM and check engine light comes on. ( checked codes 25, 26, 52 = lean/rich/knock) Always starts easy, drives, but lacks power and sputters at those highway speeds.

What next? O2 sensors, fuel pump, cap and rotor, ignition, I don't know what to try next. Thanks in advance!!

 

[ppc]

@twitchfury,

Replace the fuel filter that is mounted underneath the intake manifold. This is different from the fuel strainer in the tank.

Your 93 model does not incorporate a MAF. The air intake is measured by the volume of air not the mass. Correct terminology is AFM or VAF not MAF.

 

[LandLocked93]

Well, OEM ...
Ignitor ~ $490
Fuel pump/sock ~$350/both.
O2 sensors ~ $400/both
Spark plug wires ~ $112
Cap/rotor ~ $75/both
Fuel filter ~ $50

Replace them all for ~$1500 and know they are good.
While recommended, no guarantee of a fix.
Tho with receipts your rig is $2000 more valuable regardless (DIY labor an all).

 

[family80]

If it starts and runs fine only breaks up when under load sounds like timing to me. I would do cap rotor and wires

 

[CharlieS]

Test your O2 sensors to make sure they're working rather than just throwing parts at it. You need an oscilloscope to do it right.

I haven't tested a knock sensor, but suspect there is a way to do so, and the FSM would likely tell you.

Plugs shouldn't be "wet" - was it fuel or coolant? If fuel, seems odd that three are wet and three aren't - maybe leaky injectors? If coolant, you may want to check for a blown head gasket.

For peace of mind, check the timing (jumping the DLC pins).

Inspect the cap and rotor for arcing or damage.

And smoke test for vacuum leaks. I missed leaks when I relied on other methods.

Also, the FSM has troubleshooting procedures that are very methodical. Maybe give that a shot (or find a mechanic that will).

 

[jpoole]

Could be a torn intake hose, the larger one that runs from air cleaner to throttle body. If older/stiff these can break when handled to remove the TB and can then be mostly "closed" at idle but open up and let a lot of air in under loads when the engine moves and opens up the cracks in the tube. If you find tears you can clean/wash the hose with soapy water then wrap the cracked area with the silicone rescue tape and get back to operation while you wait on a new one to be delivered.

 

[SHIfTHEAD]

I had a similar issue when I got my 80, would run fine and then out of the blue was like a big miss. I chased many things, but thankfully it started one day and stayed in the condition long enough for me to figure out the issue. Number 1 injectors pins weren't making a good connection. Stretched the female side contacts back out a bit to give them a bit more spring again and it's been running fine ever since.

 

[mudgudgeon]

All of the above, plus check injectors are all good, and injector wiring harness.
Wiring harness is prone to damage around the EGR.

 

[twitchfury]

Test your O2 sensors to make sure they're working rather than just throwing parts at it. You need an oscilloscope to do it right.

I haven't tested a knock sensor, but suspect there is a way to do so, and the FSM would likely tell you.

Plugs shouldn't be "wet" - was it fuel or coolant? If fuel, seems odd that three are wet and three aren't - maybe leaky injectors? If coolant, you may want to check for a blown head gasket.

For peace of mind, check the timing (jumping the DLC pins).

Inspect the cap and rotor for arcing or damage.

And smoke test for vacuum leaks. I missed leaks when I relied on other methods.

Also, the FSM has troubleshooting procedures that are very methodical. Maybe give that a shot (or find a mechanic that will).

Thanks for this. How does one perform a smoke test?

 

[twitchfury]

Test your O2 sensors to make sure they're working rather than just throwing parts at it. You need an oscilloscope to do it right.

I haven't tested a knock sensor, but suspect there is a way to do so, and the FSM would likely tell you.

Plugs shouldn't be "wet" - was it fuel or coolant? If fuel, seems odd that three are wet and three aren't - maybe leaky injectors? If coolant, you may want to check for a blown head gasket.

For peace of mind, check the timing (jumping the DLC pins).

Inspect the cap and rotor for arcing or damage.

And smoke test for vacuum leaks. I missed leaks when I relied on other methods.

Also, the FSM has troubleshooting procedures that are very methodical. Maybe give that a shot (or find a mechanic that will).

Also, I have no experience with the injectors, testing them, etc. Is this a home garage mechanic job or deeper?

 

[CharlieS]

Thanks for this. How does one perform a smoke test?

Lots of ways to do it, but I use a machine that I bought on Amazon that creates smoky vapor, I hook it to my compressor at low pressure, then put the hose in an open orifice of the vehicle with one of several adapters that came with it. The simplest test is to use the cone in the intake tube. Anywhere you have a vacuum/air leak will have the smoke visible. Using a bright flashlight you can find the areas where a leak exists. You can use it in the gas fill to check for leaks there, on the exhaust tip to see exhaust leaks. Some vehicles like my son's Land rover have a port on the EGR system that you can hook into. The smoke testing machine I purchased was under $80 and I've used it to identify and repair several vehicles.

 

[CharlieS]

Also, I have no experience with the injectors, testing them, etc. Is this a home garage mechanic job or deeper?

I'd check the factory service manual. They have a solenoid type arrangement so you can hear them actuate, and you could probably measure volume and check spray pattern if you were ambitious.

I wanted to do a (300k mile) baseline, so I sent my injectors off to Advanced Injector and had them cleaned, balanced and new filters, o-rings and seals installed. They are returned with full before/after documentation. Well worth $21/injector when one new injector costs hundreds.