91 K2500 5.7 running poorly when trailer is attached

[OldmancrashMT]

I bought this truck with a rebuilt 5.7 motor with about 8500 miles on the rebuild. It has 216000 miles on the body. And a blown 700r4 transmission. As a matter of fact 2 prior blown transmissions. It had been sitting for about 2 1/2 years here in NW Montana. I had it towed home and a couple days later put in a new battery and with only a few seconds of cranking it started. Out came the transmission and to the rebuilder. In the mean time I put new drums, rotors, brakes, spring kits, Ujoints, new axle bearings, new rear gear lube, new front gear lube, shocks. Put the newly rebuilt transmission in and away we went. But it felt more like a 4cyl rather then a 5.7 big ol V8. Just would not get out of the way of its own shadow. So I decided the timing was not advancing correctly and replaced the distributor. Set the timing to 0 and then bumped it to 8deg now. Oh yeah would sit and idle just fine. It would even rev up good. But once it was put in gear it ran like crap. I have a 28 foot enclosed snowmobile trailer that I tow my SxS in and camp out of. Well we took a trip about 80 miles west. Took almost a half a tank of gas. On our return trip just a little ways out of town I blew the governor cap out of the transmission. Towed the truck and trailer to my brother in-laws house and put it up on the hoist. Replaced the cap with a new one and gasket. And after talking to a few folks they said to replace the fuel filter. So we did. Could not even blow through it. Took the air hose and barely was able to blow that through. Got chunks of crap out of it. Away we went. Seemed like it wanted to run like a champ. I was excited. Came back to the shop to get my car and the service engine soon light came on. Did some checking and found that the knock sensor was saying it was bad. Crawled under to replace it and found the connector was all broken up. Replaced the connector and the light has stayed off. But back to running like crap. Rebuilt the TBI thinking a bunch of junk got sucked up. No difference. Pulled the EGR and made a block off plate and still no power. Ran a can of CAT cleaner through and no difference. Heck I even replaced the temp sensor because I read somewhere they can cause issues. Folks, I am stumped. Runs like dog crap and just plain ol wont run. With my trailer on (about 5,000 pounds loaded) I am lucky to get 60mph. Running empty to town I can cruise about 80 but seems like it is dogged down and trying to run against its self. Any ideas? Oh yeah tonight I cut my muffler out and thinking it was plugged and while it was not great I have seen worse. Also when running crappy I get smells of old varnished fuel. I have run probably 7 or 8 full tanks of gas through it. Maybe change the fuel filter again? Try new injectors? Anyone have a TBI thats known good I can try LOL Thank you all and sorry to be long winded

 

[Schurkey]

Stop guessing. Connect a scan tool, study the data stream, find out what the computer is trying to tell you.

Verify fuel pressure under load.

When have you inspected the usual "tune up" items--plugs, plug wires, cap 'n' rotor, PCV, charcoal canister?

Would be worthwhile checking exhaust back-pressure to verify the catalyst isn't plugged/melted.

 

[OldmancrashMT]

Stop guessing. Connect a scan tool, study the data stream, find out what the computer is trying to tell you.

Verify fuel pressure under load.

When have you inspected the usual "tune up" items--plugs, plug wires, cap 'n' rotor, PCV, charcoal canister?

Would be worthwhile checking exhaust back-pressure to verify the catalyst isn't plugged/melted.

Thank you very much for your reply. I have new plugs (autolite I believe) and wires (from napa something like $70 jobber price so not super high end). The new distributor (from napa also) came with a new cap and rotor. Replaced the PCV but not the charcoal canister (will do tomorrow). I checked my codes with a blinking light (which I got from a GM transmission mechanic) which is what told me the knock sensor was bad originally. But have not checked since. I will need to scavenge up some goodies to check fuel pressure under idle and load. Also am pulling the CAT tomorrow and checking. Thank you for the idea.

 

[Schurkey]

A blinking light is not a scan tool. It's a piece-of-shiit "code-reader". You need to see the data stream--the sensor inputs, and the computer's outputs in response.

Don't "replace" the charcoal canister, TEST IT along with the hoses and control valves.

"New" distributors are almost always low-budget Chinese knockoffs. It may be OK, but be suspicious. Does the timing advance like it should?

When checking timing, are you sure the ring on the damper hasn't slipped?

Plugged fuel filters are exceptionally ******* the fuel pump. Be sure the pump is working like it should. Most fuel pressure testers have a button to release fuel pressure into a hose that leads to a container; test the fuel pressure at idle, then see what happens when you push the button so that the volume of fuel released increases.



* Oh, for fooque sakes. I can't say that a plugged filter is "ha_rd on" the pump.

 

[Erik the Awful]

If your original fuel filter was plugged, I'd definitely swap it again and keep another spare in the glove box. But, yeah, check your fuel pressure while it's running. The TBI fuel pumps are crap.

 

[OldmancrashMT]

A blinking light is not a scan tool. It's a piece-of-shiit "code-reader". You need to see the data stream--the sensor inputs, and the computer's outputs in response.

Don't "replace" the charcoal canister, TEST IT along with the hoses and control valves.

"New" distributors are almost always low-budget Chinese knockoffs. It may be OK, but be suspicious. Does the timing advance like it should?

When checking timing, are you sure the ring on the damper hasn't slipped?

Plugged fuel filters are exceptionally ******* the fuel pump. Be sure the pump is working like it should. Most fuel pressure testers have a button to release fuel pressure into a hose that leads to a container; test the fuel pressure at idle, then see what happens when you push the button so that the volume of fuel released increases.



* Oh, for fooque sakes. I can't say that a plugged filter is "ha_rd on" the pump.

Thank you. HAHAHA I was trying to figure out what word got blocked LOL Ok I just changed the fuel filter again, just now. Seemed ok. I didnt get any crap out of it. When I removed the air cleaner to just have a look around for the 1 millionth time I noticed the flapped in the air cleaner closed. Sooooo, here in a few I am going to take another test drive without the air cleaner and just see, Just a short trip around my block. *****What scan tool would you recommend? Again Thank you for your tie and help. Also going to pick up a fuel pressure tester tomorrow when I am in town.

 

[OldmancrashMT]

If your original fuel filter was plugged, I'd definitely swap it again and keep another spare in the glove box. But, yeah, check your fuel pressure while it's running. The TBI fuel pumps are crap.

Thank you. Funny, I just swapped it again and came in here to see what replies I have and you gave me this help. Thank you, maybe someday this truck will run LOL

 

[DoubleCross]

Check fuel pressure. Pump may be bad. Mine has been running sluggish and random misfires. My pump should be 61-62 lbs. It's at 50. About to change mine.

 

[Schurkey]

What scan tool would you recommend?

I have an ancient Snap-On MTG2500. The MT2500 is more common, less expensive, and nearly identical.

However, the '2500 series is old enough that, if I were buying one now, I'd probably move up to the newer Snap-On Solus family--Solus, Solus Pro, Solus Ultra, Solus Edge--in order of production timeframe. As you go newer, the price increases.

There's other options from multiple manufacturers and re-branders, including software to run on a laptop computer with a USB adapter cable--but I haven't used any of them. I'm the only guy I know with a scan tool, so I have no friends with different tools to compare.

 

[L31MaxExpress]

Check fuel pressure. Pump may be bad. Mine has been running sluggish and random misfires. My pump should be 61-62 lbs. It's at 50. About to change mine.

TBI needs about 13-14 psi to run at its peak with a stock engine. I have seen some that were gutless dogs that only held 9 psi under load.