FJ80 Intermittent Starting issues. Code 25/26 or battery issue?

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Jan 18, 2018
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Hey guys, so I give up. I’ve searched and searched for sometime now. I have been reading and trying different fixes or ideas here on the forum. Been asking a few other 80 series owner buddies of mine, but now I gotta post a thread.

As a few of you might know, I have a 91 FJ80. 250,569 on the clock. New starter (replaced around Sept. 2022), alternator replaced (2017), o2 sensors replaced (2019), egr seems to be working fine because I don’t notice any change in idle speed on cold starts. Good positive terminal connections. Redid my ground wire to the chassis.

Here’s the problem. Every now and then, I’ll have problems starting the truck after driving. I thought maybe it was a weak alternator, but checked with a voltage meter, and with the truck at idle, I’m getting 14.6V to the battery. Thought maybe my battery wasn’t holding charge, so I had it checked at autozone. Turned out it was a bad batt. Replaced with a yellow top optima. I’ve had the CEL on for about a month now. Paper clip told me it was a code 25/26.

What’s weird is that when I’m having trouble starting the truck, I attach my jumper on it, and it’ll fire up after a couple cranks. The thing is, even with the new battery, I’m getting good strong long cranks. Doesn’t sound weak at all. The engine just isn’t turning over.

When it runs, it runs very smooth. Idle is about 900 rpm. Don’t feel any bad hesitation on acceleration. Even with the code 25/26.

My question is, should I chase the code 25/26 down first? Or does this sound like a battery issue?

to me, it feels like the engine may have a vacuum leak based on how good it cranks, but then why would it start right up when a jumper is on it? Can’t emphasize it enough, really strong cranks.
 
So it cranks but wont start at times? Have you gone through the 3FE no start guide?

yes. At times it cranks but won’t start. I had previously looked through this diagnostic. Many many times over I should add because it was confusing at first. Haven’t noticed if CEL is off when the key is in the ON position, but that’s because it’s been on even when driving so I may not notice it anymore. I’d have definitely noticed if it wasn’t lit when the key is ON. I’ll try and go through the diagnostic again and try the coil and igniter diagnostic.
 
i should add; on a cold start, say after sitting overnight, the truck fires up right away. It’s when I stop for gas, or stop for a picnic, is when I have this issue.
 
If it was a battery issue you would likely have a cranking issue and if it was an alternator you would not have enough voltage to run or crank. The other problem is those two codes. odd that these are coming up considering that your o2 sensors aren't that old. Probably a good idea to inspect your engine loom.

25Mixture control -continuously leanWiring, injector, H02S, ECT/VAF sensor, intake/fuel/ignition system, ECM
26Mixture control -continuously richWiring, injector, fuel system, cold start injector, H02S, ECT/VAF sensor, ECM
 
If it was a battery issue you would likely have a cranking issue and if it was an alternator you would not have enough voltage to run or crank. The other problem is those two codes. odd that these are coming up considering that your o2 sensors aren't that old. Probably a good idea to inspect your engine loom.

25Mixture control -continuously leanWiring, injector, H02S, ECT/VAF sensor, intake/fuel/ignition system, ECM
26Mixture control -continuously richWiring, injector, fuel system, cold start injector, H02S, ECT/VAF sensor, ECM
That’s what I was afraid of. Me and looms don’t understand each other. What exactly am I looking for while inspecting the loom?
 
When it runs, it runs very smooth. Idle is about 900 rpm.
This jumped out to me.
Idle should be 650 rpm. If you're idle is 900, then the throttle cable is too tight and the throttle plate is not in the idle position. Or there is crap blocking the throttle plate from closing properly.
 
This jumped out to me.
Idle should be 650 rpm. If your idle is 900, then the throttle cable is too tight and the throttle plate is not in the idle position. Or there is crap blocking the throttle plate from closing properly.
I was wondering when @jonheld would hop on here.

Throttle plate was my thought. Was going to clean the AFM and throttle body this weekend.

Can’t remember what I’m supposed to use as a cleaner for the AFM
 
Can’t remember what I’m supposed to use as a cleaner for the AFM

There isn't anything to clean in the AFM unless you open the big sealed plug on the top and spray electronic cleaner on the circuit board which I recommend you do not mess with. Just make sure the "vane" in the air path moves freely.
 
A list of things I am going to look into.

Coil & Igniter
AFM & Throttle body
FPR and FPD
Possible relation to my code 25/26
Distributor cap & Rotor, distributor contacts, ignition wire to distributor cap.
 
There isn't anything to clean in the AFM unless you open the big sealed plug on the top and spray electronic cleaner on the circuit board which I recommend you do not mess with. Just make sure the "vane" in the air path moves freely.

Yeah I was gonna clean that area to make sure the vane moves freely.
 
I was wondering when @jonheld would hop on here.

Throttle plate was my thought. Was going to clean the AFM and throttle body this weekend.

Can’t remember what I’m supposed to use as a cleaner for the AFM
Check the throttle cable first. There should be some slack in the cable at the idle position.
 
Have you replaced the fusible links?

No CEL with ignition turned on before starting means the ECM is not receiving power and will never start.
 
Have you replaced the fusible links?

No CEL with ignition turned on before starting means the ECM is not receiving power and will never start.

Replaced the fusible link with a kit from Wits-End back in 2017. Have a brand new spare here as well. CEL is lit when in the ON position.

Haven’t noticed yet if it’s lit when the issue returns, but I haven’t been able to replicate the issue when I want to.
 
Makes no difference.
Will do.

Here’s a serious question @jonheld

When checking the resistance on the coil pickups, is the battery supposed to be hooked up? Or should I disconnect the battery before doing this?
Makes no difference. You're reading static resistance across coils.
BTW, if the coils were faulty, the engine would not run.
 
Makes no difference.

Makes no difference. You're reading static resistance across coils.
BTW, if the coils were faulty, the engine would not run.
Ok. So if the coil was faulty It would just go out? Not like this intermittent starting issue? Gonna be driving it to work tonight. I’ll update
 
alright, so no CEL with key in ON position.
Parked and turned the engine off. Turned it back to ON position, and no CEL. Engine cranks and cranks but doesn’t go.

Going through the Diagnostic procedure spreadsheet for the 3FE.

1) Dome light working? Yes
2) Charge Light on? Yes
3) Brake lights working? Yes

So nothing wrong with all 3 fusible links.

Narrowing it down to AFM short or EFI relay.

I am leaning towards the EFI relay because after the truck sits for a while, it’ll fire right up again.
 
Your blower relay in the kick panel and the EFI relay are the same, if your blower works on high then swap the relays. should rule out the EFI relay quick.

It might not be the blower motor relay, but im pretty sure one of the ones in that kick panel are the same as the efi
 
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Your blower relay in the kick panel and the EFI relay are the same, if your blower works on high then swap the relays. should rule out the EFI relay quick.

It might not be the blower motor relay, but im pretty sure one of the ones in that kick panel are the same as the efi
What’s funny is the my blower doesn’t work on high. When I max out the blower, it actually gets weak. So it’s goes like , “weak, strong, stronger, weak” haha.

But I do have an extra relay sitting in the truck right now. Will go on my lunch break.
 

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