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89 k5 power loss under load

T

travis565

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las vegas
Hey yall,
I've been searching for help on this issue but I can find anything either problems like I'm having. Truck cranks and idles fine rev up is ok a few misses nothing major but as soon as I put it in drive and the rpm goes up to about 1200 it starts missing and sputtering and loses all power. Doesn't shut off but a strong wind will slow the truck down . It seems like it takes a min to change from first to second gear too . if I try to stomp it to passing gear it just bogs and doesn't go anywhere. You would think it goes from a 350 tho to a Briggs and Stratton . The only way I can get up to say 35mph is to feather the gas from wide open to foot off and it'll creep up but that's it.
Now I've replaced the egr about 2 yrs ago along with the throttle position sensor. I believe I've changed the map sensor too. Just replace the ignition control module again today . Noticed the cap and rotor needs to be replaced too but just don't want to throw money at it hoping it'll fix. I don't hear or notice and sparking from the wires. Replaced the fuel pump when I changed the egr. Also rebuilt the tbi back then too along with the computer. The only thing I can think of is the fuel pump relay , fuel pump pick up hose , filter, clogged cats which are about a yr old too. O2 sensor which is about 2yrs old. Anything past that I'm stumped. Thing idles like it should no lopes or anything. Acts like it's running lean. No gas smell at all. I pulled vacuum off the egr and sensor didn't change. Maybe someone else has dealt with this? I thought maybe the magnetic pick up on the dist. But wouldn't that be constant and not just under load. Any insight would be greatly appreciated!
 
travis565 said:
Hey yall,
I've been searching for help on this issue but I can find anything either problems like I'm having. Truck cranks and idles fine rev up is ok a few misses nothing major but as soon as I put it in drive and the rpm goes up to about 1200 it starts missing and sputtering and loses all power. Doesn't shut off but a strong wind will slow the truck down . It seems like it takes a min to change from first to second gear too . if I try to stomp it to passing gear it just bogs and doesn't go anywhere. You would think it goes from a 350 tho to a Briggs and Stratton . The only way I can get up to say 35mph is to feather the gas from wide open to foot off and it'll creep up but that's it.
Now I've replaced the egr about 2 yrs ago along with the throttle position sensor. I believe I've changed the map sensor too. Just replace the ignition control module again today . Noticed the cap and rotor needs to be replaced too but just don't want to throw money at it hoping it'll fix. I don't hear or notice and sparking from the wires. Replaced the fuel pump when I changed the egr. Also rebuilt the tbi back then too along with the computer. The only thing I can think of is the fuel pump relay , fuel pump pick up hose , filter, clogged cats which are about a yr old too. O2 sensor which is about 2yrs old. Anything past that I'm stumped. Thing idles like it should no lopes or anything. Acts like it's running lean. No gas smell at all. I pulled vacuum off the egr and sensor didn't change. Maybe someone else has dealt with this? I thought maybe the magnetic pick up on the dist. But wouldn't that be constant and not just under load. Any insight would be greatly appreciated!
Click to expand...

Forgot to mention it's a 350 tbi with 700r4
 
Don't see anywhere there that plugs are known to be good.

I don't like throwing money at these problems either, you've spent a fair bit already and the problem persists, so you know why I feel that way too.

IMO the cap and rotor can be checked and given a thumbs up as long as the terminals are tight, corrosion free, and no physical damage. Scrape corrosion off, sand them lightly, whatever is needed to make them look good. Obviously wear from corrosion should mean replacement. But some light corrosion is pretty normal with age.

Wires and plugs are tough. Both can fail and you won't see the issue by an inspection. Injection seems (IMO) to do such a good job at fueling that a dead or weak cylinder may not even be evident. Pulling plug wires one at a time while it's running can help pinpoint a problem related to one cylinder.

If the plugs are excessively worn, replace them with the spec'd AC Delco plugs. Don't buy the aftermarket hype, put the stock plugs in to make sure you don't introduce other problems.

Do you hear any pinging? Possible you've got some pinging going on which retards timing, and that would be evident under load.

A "quick" check of the fuel system can be done by running to Autozone, borrowing their fuel pressure test set, and hook it up to the engine side of the fuel filter (easier to access, less likely to screw the fittings up there). GM spec is 9-13PSI, anything under about 10 can cause issues.
 
I didn't see anything regarding the ignition coil in your list of things replaced..


A weak ignition coil can cause power loss under a load,weak spark always shows up most under load...sometimes a coil works fine until its been run awhile,then it'll crap out --if the secondary windings short out after getting hot it'll reduce the voltage going to the spark plugs,and the spark will "blow out" under compression rather than fire the plugs..

A faulty pick up coil can also cause the same thing,since it "tells" the coil and module when to fire...they can be out of spec and still let it run,but poorly..
I'd also make sure the ground strap or wire to the coil is hooked up..
 
dyeager535 said:
Don't see anywhere there that plugs are known to be good.

I don't like throwing money at these problems either, you've spent a fair bit already and the problem persists, so you know why I feel that way too.

IMO the cap and rotor can be checked and given a thumbs up as long as the terminals are tight, corrosion free, and no physical damage. Scrape corrosion off, sand them lightly, whatever is needed to make them look good. Obviously wear from corrosion should mean replacement. But some light corrosion is pretty normal with age.

Wires and plugs are tough. Both can fail and you won't see the issue by an inspection. Injection seems (IMO) to do such a good job at fueling that a dead or weak cylinder may not even be evident. Pulling plug wires one at a time while it's running can help pinpoint a problem related to one cylinder.

If the plugs are excessively worn, replace them with the spec'd AC Delco plugs. Don't buy the aftermarket hype, put the stock plugs in to make sure you don't introduce other problems.

Do you hear any pinging? Possible you've got some pinging going on which retards timing, and that would be evident under load.

A "quick" check of the fuel system can be done by running to Autozone, borrowing their fuel pressure test set, and hook it up to the engine side of the fuel filter (easier to access, less likely to screw the fittings up there). GM spec is 9-13PSI, anything under about 10 can cause issues.
Click to expand...

Thanks for the reply bud. I haven't pulled the plugs yet to see what's going on cylinder wise. I plan on doing that this afternoon and replacing cap and rotor just to rule that out. Since it's cheap enough. And I'll borrow that fuel pressure tester while I'm at it. I didn't hear any pinging or knocking either but I have loud exhaust so that might drown it out a bit too. I'll def repost with my findings after work
 
diesel4me said:
I didn't see anything regarding the ignition coil in your list of things replaced..


A weak ignition coil can cause power loss under a load,weak spark always shows up most under load...sometimes a coil works fine until its been run awhile,then it'll crap out --if the secondary windings short out after getting hot it'll reduce the voltage going to the spark plugs,and the spark will "blow out" under compression rather than fire the plugs..

A faulty pick up coil can also cause the same thing,since it "tells" the coil and module when to fire...they can be out of spec and still let it run,but poorly..
I'd also make sure the ground strap or wire to the coil is hooked up..
Click to expand...

I failed to mention I replaced the coil back when I did all the other stuff too. I put an msd coil in there while I have it apart today ill check for the grounds . Hopefully it's just something as simple as that!
 
I would throw a fuel filter on it, just because they are cheap, and should be replaced fairly regularly any way.

Martin
 
If it still has a catalitic converter it might be clogging up too..
Also see if the EGR valve is opening when it should not..
 
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