Please help with my first truck

[Jaxson4x4]

I bought a 1998 Silverado 2 days ago knowing it had some “misfire” problems but I didn’t know the causes, I’ve replaced the rotor cap and rotor and nothing really changed, sometimes it take 3 cranks to start up and sometimes it fires right up. I’ve put a video of it running, it won’t go past 25mph. I’ve bought a lot of parts and have some ideas at what it is but wanna see if anyone on here has any ideas. Thanks

Running video here - Btw truck sounds worse with a stronger “knock” in the video than in person
Driving video here

 

[thegawd]

there you are. like I said on the other site... a fuel pressure test needs to happen, a lot of your symptoms could be caused by a bad pump. Also test the TPS to make sure it isn't faulty as a faulty tps screwes with shifting...

Al

 

[Schurkey]

How old are the plugs, and plug wires? How old are the O2 sensors? Are the vacuum hoses connected properly? Does the EGR system work right?

Catalyst(s) plugged? When the converter plugged on my Trailblazer, I went from 80 mph to barely able to crawl into the repair shop, in under 50 miles. Wouldn't even go 25 mph--more like 3 mph.

Connect a scan tool, look at the codes, but more-importantly look at ALL the sensor data, and the output data--IAC, EGR, AIR pump solenoid (if equipped), spark advance, etc.

My '97 K2500 had terrible misfire history on #8 when I bought it. Ran bad, problems starting, no Torque Converter Clutch, either.

Turned out, #8 spark plug had a cracked porcelain. Screwed in a used spark plug from the L29 Vortec 7.4L cylinder heads I took off my boat. Misfire gone, and the computer disables the TCC when it senses misfire, so that spark plug fixed the engine AND the TCC.

 

[Jaxson4x4]

How old are the plugs, and plug wires? How old are the O2 sensors? Are the vacuum hoses connected properly? Does the EGR system work right?

Catalyst(s) plugged? When the converter plugged on my Trailblazer, I went from 80 mph to barely able to crawl into the repair shop, in under 50 miles. Wouldn't even go 25 mph--more like 3 mph.

Connect a scan tool, look at the codes, but more-importantly look at ALL the sensor data, and the output data--IAC, EGR, AIR pump solenoid (if equipped), spark advance, etc.

My '97 K2500 had terrible misfire history on #8 when I bought it. Ran bad, problems starting, no Torque Converter Clutch, either.

Turned out, #8 spark plug had a cracked porcelain. Screwed in a used spark plug from the L29 Vortec 7.4L cylinder heads I took off my boat. Misfire gone, and the computer disables the TCC when it senses misfire, so that spark plug fixed the engine AND the TCC.

Plugs and wires are brand new according to the guy who sold me the truck, I’m going to re do them tomorrow, also did you cut your cat off? I’m thinking that is what’s not letting me go past 25mph. I’m also going to look at codes tomorrow and I can post them here

 

[Schurkey]

Plugged catalyst was replaced with a "universal" aftermarket cat.

 

[Jaxson4x4]

there you are. like I said on the other site... a fuel pressure test needs to happen, a lot of your symptoms could be caused by a bad pump. Also test the TPS to make sure it isn't faulty as a faulty tps screwes with shifting...

Al

Here’s what I did yesterday with my neighbor… fuel pressure test came out at 60/55 psi, compression test came out at 170/175 across all cylinders, spark plugs and wires are brand new but cleaned them up, he said I was getting 2 misfires codes and one for MAP sensor. He recommended I try to get a scanner to see which 2 cylinders are misfiring then get the 2 fuel injectors for those cylinders… and get a new map sensor

 

[thegawd]

if the mpfi is original it does have some flaws. there are new units available with those flaws fixed.

its awesome that all those important parts are checking out! if the fuel injection is not spraying then those cylinders will never fire.

Your off to a great start man!

CHEERS

 

[Jaxson4x4]

there you are. like I said on the other site... a fuel pressure test needs to happen, a lot of your symptoms could be caused by a bad pump. Also test the TPS to make sure it isn't faulty as a faulty tps screwes with shifting...

Al

Here’s what I did yesterday with my neighbor… fuel pressure test came out at 60/55 psi, compression test came out at 170/175 across all cylinders, spark plugs and wires are brand new but cleaned them up, he said I was getting 2 misfires codes and one for MAP sensor. He recommended I try to get a scanner to see which 2 cylinders are misfiring then get the 2 fuel injectors for those cylinders… and get a new map sensor.

if the mpfi is original it does have some flaws. there are new units available with those flaws fixed.

its awesome that all those important parts are checking out! if the fuel injection is not spraying then those cylinders will never fire.

Your off to a great start man!

CHEERS

I FIXED MY TRUCK!!
One of the cats was plugged so I un hooked it and it ran way better, just dropped it off at the muffler shop so he can cut them off and weld pipe on.

 

[Schurkey]

just dropped it off at the muffler shop so he can cut them off and weld pipe on. I am so excited

That's a $10,000 fine for the shop that does that. Good luck.

 

[Jaxson4x4]

I don’t think it is where I’m from, in North Dakota we don’t have emission testings