Misfiring under load.

[Holt50]

97 gmc yukon 380.000 miles. 4x4 4 door
Changed the fuel pump idols fine but when you give it gas it starts to misfire and sputters real bad. What to do now?

 

[OR VietVet]

Just replaced the pump on a whim or guess or did you do a pressure test? Fuel filter? What is the age and brand names of the ignition components? Last time tune work done? Lots of unknowns here and need the basics first.

 

[Holt50]

Well it ran fine. Then I had a little fuel leak. I broke the plastic pulling the hose off the pump. Had to buy new pump and also got a new filter.
I don't remember the brand of distributer or plugs and plug wires. It's been probably around 5 to 7 years since last tune up. Wouldn't you think it's fuel since that's all I messed with.
It idols fine and when it's in park I can rev it up and there's no misfire. But when I start driving it is also fine at low speeds it's just when I floor it then it gets crazy misfiring sputters all that good stuff

 

[OR VietVet]

So, you were messing with or replacing the fuel pump with no misfire? Why were you in there to work on or replace anything? Start telling the whole story. If you had no problems till you did deal with the fuel pump, then you are right, likely related. The whole story would be very helpful instead of me pulling teeth to get the whole story. 5 to 7 year old ignition components, without knowing the mileage-again-no info, still says that you deal with breakdown maintenance instead of preventative maintenance. I promise you, I am ragging on you a bit mainly because you are not sharing the whole story. Vehicle Detective @OR VietVet signing off for now.

 

[Holt50]

Hey bro go back and read the post it says that there was a fuel leak. And the mileage is also there. So before being a dick you should make sure what you're saying is all 100 % correct. So since you aren't sure and you want to be a dick I don't need your ******* help.

 

[exp500]

Insults against members trying to help you is one good reason for others here to ignore you. Good luck.
Fire up the parts cannon!

 

[swathdiver]

If yours were mine I'd pull the spark plugs and inspect them. If they're good, still holding the correct gap, wires look good, I'd start looking at the catalytic converters.

 

[Fless]

Without sounding like the Inquisition, it seems like some basic health report info would be helpful. Any codes?

Condition and age of plugs and wires, cap and rotor?

Can you see individual cylinder misfires on a scanner?

Fuel pressure readings?

Since it seems to have started after the fuel pump change (right?), something that was done during that repair may have caused it, or possibly a bad fuel pump out of the box. If tests rule out fuel delivery, move on to dry and wet compression tests and catalytic converter tests.

 

[OR VietVet]

Hey bro go back and read the post it says that there was a fuel leak. And the mileage is also there. So before being a dick you should make sure what you're saying is all 100 % correct. So since you aren't sure and you want to be a dick I don't need your ******* help.

Your first post does not mention a fuel leak at all as a reason to change the pump. Your second post makes it sound like you created a fuel leak working on the fuel pump replacement. The post sounds like you were working in the fuel pump area and then broke the plastic pulling the line off and then had to buy a pump because of that. That makes me wonder why you were in the fuel pump area to begin with and therefore I wanted that info, in chronological order. But that is ok. I have pretty thick skin but I do draw the line at being called "bro" as a Vietnam vet. None of us like that. By the way, the current mileage is listed but that does not tell me the miles on ignition components or even the fuel pump. Last but not least, we would always want to know of any CEL.

Your very first statement of the second post, "well it ran fine" does not tell me or anyone else when it ran fine. Before you messed with the fuel pump? After the fuel pump? If you think about it in steps, telling us the chronological order of events really helps when we are trying to piece the story together and come to a conclusion. Have a better day.

 

[Eman85]

This seems to be a big thing on forums now. Someone asks for help and then gets insulting to someone that questions them about the problem in an attempt to help them. Goes the other way too on some forums when someone asks an honest question and the responses are insulting.
Now..to the problem. Information is the key to getting good advice on the repair. If it runs OK without a load but when put in drive it misses it sounds like a possible fuel pressure problem or ignition misfire. Do you have a fuel pressure gauge? A pressure reading would be helpful. One quick check for ignition misfire is to use a spray bottle and mist water around the plugs and wires as someone puts it in drive and loads the motor a little.

 

[dnt1010]

I had a 97 and it destroyed distributor caps on a fairly regular basis, (well it was driven +50k
per year so once a year a new cap LOL) that would be my first move to swap on a new distributor cap.
The design was very prone to cross firing inside, when you take it off look for carbon tracks inside. Takes about 10 minutes and most likely your problem will disappear.

 

[YukonGTmaster]

Have a good look at the spark plugs again. When I had my intake leak, the plugs would foul up so badly, the gap was completely bridged with crud.

 

[Holt50]

First of all the insults came after this guy well was being a better than you and your stupid in so many words kinda dick.
Soooooooo yeah I'm gonna say something. Anyway truck is running like a champ again for no reason just stopped misfiring. Probably because I had a long talk with her. Anyway thank you everyone who tried helping me very appreciated

 

[B-train]

The weather can have an impact kn bad ignition components. Rainy weather will make them worse, etc. Since it cleaed up, use the info given here and keep a mental note of what, why, when, how.....

Best of luck

 

[Holt50]

The funny thing will maybe not to funny is that it still comes and goes

 

[Holt50]

Now I'm thinking it could be it only happens when I'm low on fuel. It started again this morning then it was getting worse I stop got fuel now it's fine.

 

[Holt50]

I had a 97 and it destroyed distributor caps on a fairly regular basis, (well it was driven +50k
per year so once a year a new cap LOL) that would be my first move to swap on a new distributor cap.
The design was very prone to cross firing inside, when you take it off look for carbon tracks inside. Takes about 10 minutes and most likely your problem will disappear. View attachment 377438

I'll do that today when I get home. I have to change my temperature sending unit. So I'll do that also thanks

 

[Fless]

Might be good to take some fuel pressure readings. One with key on, engine off (KOEO) and maybe monitor the fuel pressure while driving it to see what the FP is doing when it misses. If it has a fuel filter, has it been changed?