Troubleshooting rough engine

T

tshort

New member
New to the forum, thanks in advance.
I have a 1996 4Runner, 5 speed, 3.4LV6 that I've owned since new, now has 315,000 miles on it. Basically trouble free aside from routine maintenance.

The other day I was running late for an appointment. Car was out of gas, so I poured in a gallon of (pretty old) gas that I had sitting in an old WWII metal Jerry can. On the way to the appointment, the car began running rough and I got a blinking check engine light. I have since refilled with fresh gas, but the problem persists.

I am assuming that the issue is related to gas, although I suppose that could be a coincidence. I'm comfortable working on just about anything, and have another car that I can drive while fixing this.

Looking for input on how to go about troubleshooting / where to start.

Thanks!
 
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Check fuel filter - do you have a code?

How much gas did you add? How much did you refill with since the issue?

If it was really old - it's possible that it started to seperate and you just have water mixed in at this point.

If you're getting a CEL, check what the code is. You may need a new injector(s).

Oh and you can just try pouring seafoam into your fuel tank. It's a fairly strong solvent and may clean up old fuel gunk and will absorb moisture.
 
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No code, yet - working on that.

I poured in a can of seafoam earlier this AM ... will see how it works.

I was wondering about the fuel filter ... far as I know, it is original.

I added probably ~1 gallon; the tank was then refilled almost completely shortly thereafter (15+ gallons).

Thanks...
 
if you have water in the tank you don't want to add sea foam. because water is too thick to go through the injectors. (works on carb engines) that is one problem about it.

change the fuel filter
 
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tshort said:
No code, yet - working on that.

I poured in a can of seafoam earlier this AM ... will see how it works.

I was wondering about the fuel filter ... far as I know, it is original.

I added probably ~1 gallon; the tank was then refilled almost completely shortly thereafter (15+ gallons).

Thanks...
Click to expand...

If the fuel seperated and you got water mixed in, it will be at the bottom of the tank and will run like ass until it's either drained or used up. Water can also damage the injectors. Just how much water will do damage or just how old the fuel has to be is a mystery. Some cars will run like champs on 5 year old gas, others will struggle on 8 months +.

Personally, I'd drive it till half tank, fill up again and drive as usual till on low. Then replace the fuel filter. All will probably be well at that point. But that is an admitedly somewhat reckless approach.

If you keep driving at worst, you may break the injectors - but then you may have already so it's up to you how you proceed. But hey - I got some injectors to sell if yours are shot :eyebrows:

Here's the write up for the filter replacement.
5VZ V6 4runner fuel filter write up with pics

The most conservative approach would be to pump out your fuel tank, change filter, put in fresh fuel and hope for the best. Pumping out fuel is a huge pita though...and I like to take my chances.
 
an easy way to get the small amount out at the bottom is to take off the fuel lines and run the fuel pump. so it sucks it out but not into the system. (into a bucket or something)
 
I've driven probably 50-60 miles since it started, all but 5 or so on the fresh tank (mixed with whatever was in there).

Aside from the slight power loss, is there any real risk of (severe) damage if I continue to drive it for a bit?

I just warmed it up and checked the exhaust headers with an infrared thermometer; it is running on all cylinders. It just has a slight roughness, and the exhaust sorta goes thump-thump-thump-thump.
 
shootmymime said:
if you have water in the tank you don't want to add sea foam. because water is too thick to go through the injectors. (works on carb engines) that is one problem about it.

change the fuel filter
Click to expand...

Seafoam is actually a very good thing to add to fuel with water as it unlike fuel does mix with and absorbs water:
Sea Foam | Why Sea Foam Motor Treatment Works | General Content - Motor Treatment

Water also goes through the injectors just fine - it's hardly any thicker than fuel. The issue is that fuel acts like a lubricant for injectors, water does not. Fuel injectors that had water run through will generally end up stuck open.
 
tshort said:
Aside from the slight power loss, is there any real risk of (severe) damage if I continue to drive it for a bit?
Click to expand...
Well - injectors...which may get stuck open resulting in running rich, which will cause slow damage to your cat if you just keep on driving...

You should see misfire codes, these range P0300-P306. P300 in random/multiple, others is P30X where X is the cylinder.
 
Looks like cylinder #4 (P0304).

I'm not terribly worried about the cat ... mine disappeared one night several years ago, courtesy of a battery powered recip saw and some thieves in the neighborhood. It's been replaced by an el-cheapo drop in from the shady muffler shop downtown.

What is the best way to troubleshoot the misfire?
 
Thanks for the reference!
I notice it says "2002 4runner" at the bottom - does it apply pretty well to the 1996 model as well?

I pulled the #4 spark plug and it looks normal. Going to drive it a bit, as I am out of time for further troubleshooting right now...
 
tshort said:
Thanks for the reference!
I notice it says "2002 4runner" at the bottom - does it apply pretty well to the 1996 model as well?

I pulled the #4 spark plug and it looks normal. Going to drive it a bit, as I am out of time for further troubleshooting right now...
Click to expand...

Yeah. The 2002 manuals are the best references as they cover the funky AWD system and other crap that got added on. In terms of the engine, I don't think anything is different in the later years other than the intake manifold and throttle body.
 
Update:

I figured I would swap the fuel filter before getting more involved in the engine compartment; not sure it will fix anything, but it can't hurt.

Problem is, after 17 years and 315K+ miles, the fittings are not coming off. I have the right tools, have soaked the fittings in liquid wrench type stuff, and they won't budge. The metal is quite soft and deforms under the wrench. Obviously the blowtorch trick isn't going to work here ... any other tips or tricks? The aft fitting is on a piece of fuel line that is 12" or so long (to the next fitting), so it shouldn't be terrible to replace, but that assumes I could get the next fitting apart.
 
i imagine your using 2 wrenches (one pulling and one pushing) to beak that connections loose correct? i want to say it like a 14 on the fuel line side and a 16 on the filter side. and its still twisting?
 
Yep. One on the fitting and one on the filter.

I don't have metric flare nut wrenches on hand ... gonna let it soak a bit longer until I can try one of those.
 
theizzardking said:
just read this (part of it at least), if your worried about water in the fuel you use heet, not sea-foam...
Click to expand...


Yeah; but also worried about general crud in the fuel as well.

Since it hasn't improved with fresh gas and additive, and is throwing a single cylinder code rather than random ones, I doubt this is the culprit. Can't hurt to change it, though. Assuming I don't trash the fuel lines....
 
tshort said:
Yeah; but also worried about general crud in the fuel as well.

Since it hasn't improved with fresh gas and additive, and is throwing a single cylinder code rather than random ones, I doubt this is the culprit. Can't hurt to change it, though. Assuming I don't trash the fuel lines....
Click to expand...

oohhh....single cylinder code after bad gas....check injectors..thats a very small hole that can get gunked up easily...replacing the fuel filter like you are is a good idea!
 
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