1991 6.2 low miss on acceleration

[Matt C]

Been way too long since I've been on here, my 1993 was just way too reliable I never needed to monkey with it, finally retired it do to rust. Bought a 1991 2500 6.2 J code. Issue started a few months back when accelerating between 2,000 and 2,500 rpm it kinda cuts out or almost like a misfire, get a little whiff of unburt fuel and it seems underpowered. Not new to the power of theses this is my 4th one, first non emissions so I was expecting better not worse. I know it's not good for the motor but for testing purposes if I momentarily flip my manual cold advance/high idle switch it doesn't seem to act up and has way more power. I have advanced the static timing and turned up the fuel screw. Truck info, 1991 6.2 J code, 4l80e, 3:73 gears, 165,000 miles. Kinda leaning towards a pump issue but looking to pick some brains. Thanks in advance

 

[Will L.]

Verify air filter is good/ no restrictions.

Clear ip return line look good? Sometimes you need a go pro/ old phone recording under the hood while driving to recreate it. Aeration of fuel or water/ algae can cause it.

Fuel pressure gauge tapped in steel at the inlet of the ip so you can read it while driving. Inside the fuel line restriction that comes free and replugs like the famous flapper inside the line issue can cause this as well as simple surging from lift pump. Low incoming pressure wipes the head & rotor. The key to long ip life is improved fuel filtration and proper incoming pressure with good lube. Never use emulsifiers like “diesel 911” or mystery marvel oil.

Injectors can cause it. If you can recreate while parked- hold the rpm there and crack injectors one at a time to id if it’s specific cylinders. Caution where buying new ones and having them adjusted to within 25psi of each other pays for itself in mpg over time. Remember they are best rebuilt at 100,000 mile intervals.

Turbo stories?

If no answers there- go real heavy on the fuel lube- see if that cleans it up.

 

[Matt C]

Haven't put a clear line on the return yet, not ruling it out or anything but when my 83 had air getting in it started like shit, this thing fires right up and runs smooth, but I'll get a clear line on it. Never been able to get it to do it unless under a load/acceleration not sitting still. What's everyone using for fuel lube these days, I user to be religious at adding 2 cycle oil but I'll admit I haven't been very good at it with this truck, don't worry I refuse to use 911 in anything, really don't like power service period

 

[Will L.]

fuel-line.com sells a clear fuel hose by the foot that is rated for all fuels.
Definitely outlasting the hardware store stuff.

Db2- atf is my preferred additive. Might hurt the spotted tree whales but the LP, ip, injectors enjoy a better life. Stanandyne still makes their additive.

 

[Matt C]

I dumped a stiff dose of dextron 3 in it and I'll drive it on my lunch break. The return line is 1/4" iirc?

 

[Matt C]

Little update, I added a gallon of atf and a overdose of howes to 1/4 tank of fuel, keep in mind a 36 gallon tank so still decent amount of fuel. Let it idle 45 min before 20 mile round trip for lunch. Drove it decent at first then got more aggressive with it, usually drive pretty nice. Didn't seem to spit and sputter and seemed to be back up on power. As a mechanic by trade I'm always pretty skeptical about fix in a bottle, but I have to remember the db2 was designed for low Sulphur not ultra low Sulphur diesel, and here in MN we get 10% bio added. Plus this truck sat around for quite awhile before I bought it. I'll keep updating but so farmight have been a simple fix

 

[dbrannon79]

I would steer clear on the howes additive. read up on the contents. some of these additives use alcohol and other chemicals that will strip out oils and make the diesel absorb water. I have used howes freeze protection in past winters and noticed my fuel mileage went to with it. just use caution with additives. theres noting like good old ATF and marine grade 2 cycle oil!!

 

[Will L.]

Yeah… the Howes is not good for it.
The ATF helped the worn pump. It isn’t a fix, you will have this reoccurring in the future. It will do this again and also get to hard starting where dousing cold water on it can help to start in the last few thousand miles of it if you wait that long.
Could get 10k- 60k more- just depends how bad it is and lube used @ what pressure.

Plan a new ip, include a “T” fitting at the pump inlet and thats where you screw in your fuel pressure gauge sensor for the dash mounted gauge.
You wanna keep the pressure above 3 all the time, closer to 5 is better. Never over 8. Ya might get that on there and keep pressure up enough to get descent amount of miles from this one yet.


Do the trick of water misted into intake to eliminate carbon crom those injectors and it might help more. Lil here, lil there all adds up.

 

[Matt C]

The eventual plan for this truck is to pull the 6.5 na crate motor out of my 93 and put in here and sell this 6.2, MN winters rotted the frame on the 93 but that engine is in excellent condition, just not ready to do it yet. So if I can get a year or 2 out of this that's all I need. Thanks for all the advice and I'll keep updating

 

[jrsavoie]

The eventual plan for this truck is to pull the 6.5 na crate motor out of my 93 and put in here and sell this 6.2, MN winters rotted the frame on the 93 but that engine is in excellent condition, just not ready to do it yet. So if I can get a year or 2 out of this that's all I need. Thanks for all the advice and I'll keep updating

You can do the fuel pressure gauge anytime.
Nothing wasted there.