Tired 350 TBI, suggestions to wake it up a bit?

[Darth Plasma]

Just finished rebuilding my 1987 V10, rebuilt and finished everything except the engine and tranny, it’s got a 1990 350 TBI and a 700R4 paired with it, and after driving it the last few days the engine doesn’t sound too healthy, it struggles with hills and when downshifting a higher gear, something starts to smell like burning, and the service engine soon usually comes on with a EGR system code (just replaced the EGR valve) And in general the idle isn’t the smoothest when hot and it does have an old tired sound to it. The spark plugs are pretty crusty and it needs a tuneup, but I’m wondering if it’s just always going to be this way from 217,000 miles. I replaced the EGR valve and O2 sensor, but I do get a slight hissing sound and I wonder if there’s a vacuum leak with the EGR valve when I put it on. The 700R4 has no issues so far. Shifts great and doesn’t slip. Any suggestions for getting it to limp a little better and a little longer? I’d LS swap it but funds aren’t permitting me for that

 

[1987 GMC Jimmy]

Just finished rebuilding my 1987 V10, rebuilt and finished everything except the engine and tranny, it’s got a 1990 350 TBI and a 700R4 paired with it, and after driving it the last few days the engine doesn’t sound too healthy, it struggles with hills and when downshifting a higher gear, something starts to smell like burning, and the service engine soon usually comes on with a EGR system code (just replaced the EGR valve) And in general the idle isn’t the smoothest when hot and it does have an old tired sound to it. The spark plugs are pretty crusty and it needs a tuneup, but I’m wondering if it’s just always going to be this way from 217,000 miles. I replaced the EGR valve and O2 sensor, but I do get a slight hissing sound and I wonder if there’s a vacuum leak with the EGR valve when I put it on. The 700R4 has no issues so far. Shifts great and doesn’t slip. Any suggestions for getting it to limp a little better and a little longer? I’d LS swap it but funds aren’t permitting me for that

It shouldn’t be. My TBIs aren’t monsters, but they’ll scream and get out of their own way. The best thing to do is to make sure your fuel pressure and fuel filter are good, no vacuum leaks of any kind, and a fresh ignition system with an appropriate timing setting to make sure you’re getting the best spark at the best time. Something’s not right there, and you probably have a serious vacuum leak on your hands or even a MAP sensor issue. The valve doesn’t do anything at idle unless it’s broken, but you can always plug off the line and see if it does better without it. My assumption is that it won’t, and the issue is elsewhere.

 

[HotRodPC]

My dad's 94 TBI 350 has to to have close to 300,000 miles on it by now and it still runs just fine. I don't think I'd give up on it just yet. I'd do the tune up parts. Plugs, Cap, Rotor, and wires too if they haven't been done in the last 80-100,000 miles. Maybe some Sea Foam treatment in the fuel tank to gradually clean the fuel system a bit and see what you get. Tracking down that SES light would be wise too. Something as simple as a MAP, MAF or o2 sensor can make a TBI system run like hell and weak.

 

[MrMarty51]

I like to install a new timing chain/sprocket set at about 200,000 miles, along with an oil pump and pan gasket. Toughest part about the oil pump is getting the oil cooler hoses out of the way, if so equipped.

 

[Darth Plasma]

Thanks guys, I just replaced the gas tank, fuel pump and filter so I think the fuel is good, I think what I’ll do is run some various vacuum tests for leaks and replace a couple sensors and give it a nice tuneup. I’ll check the timing on it too. I agree it runs like absolute crap and it probably shouldn’t

 

[78C10BigTen]

Mine is carbed but i get the same thing on hills, its a dog and takes quite awhile to reach speed. I think mines a distributor issue. Soon as i get to it ill be ordering a skip white for it.

 

[Darth Plasma]

Mine is carbed but i get the same thing on hills, its a dog and takes quite awhile to reach speed. I think mines a distributor issue. Soon as i get to it ill be ordering a skip white for it.

Yeah I have no idea how long ago mine was tuned, the PO didn’t give a crap about anything except that it ran so I think I know what I gotta do

 

[78C10BigTen]

Yeah I have no idea how long ago mine was tuned, the PO didn’t give a crap about anything except that it ran so I think I know what I gotta do

I passed you last night on the road from mainvile to mifflinville. I waved to ya lol

 

[1987 GMC Jimmy]

Make sure you replace the CTS if you’re going through sensors. Those can go bad over time, and your computer can indiscriminately richen your AFR.

 

[Darth Plasma]

I passed you last night on the road from mainvile to mifflinville. I waved to ya lol

Aw man I didn’t see you, I would have waved back

 

[Triv]

Get a vacuum pressure tester. They are cheap and will tell you if you have a leak. Sounds like you do.

I have an '87 TBI 350 and I put headers, throttle body spacer, jet stage 1 chip, and a K&N air filter and it woke the truck right up. Huge difference. Oh, I also rebuilt the TBI, which helped big time too.

Probably want to start with a tune up though.

 

[4WDKC]

an exhaust leak will cause the truck to run poorly fix any exhaust leaks. The stumble with the EGR is a symptom of an exhaust leak, the truck is lean and egr opens making it worse. What size tires are on the truck and what gears are in it?

 

[Darth Plasma]

Get a vacuum pressure tester. They are cheap and will tell you if you have a leak. Sounds like you do.

I have an '87 TBI 350 and I put headers, throttle body spacer, jet stage 1 chip, and a K&N air filter and it woke the truck right up. Huge difference. Oh, I also rebuilt the TBI, which helped big time too.

Probably want to start with a tune up though.

I’m starting with a tuneup and doesn’t the propane trick work for testing vacuum leaks? Mine has a throttle body spacer and long tube headers as well

 

[Darth Plasma]

an exhaust leak will cause the truck to run poorly fix any exhaust leaks. The stumble with the EGR is a symptom of an exhaust leak, the truck is lean and egr opens making it worse. What size tires are on the truck and what gears are in it?

I just put a new exhaust on and it runs better and new O2 sensors, just put the factory 15”s on and I’m not sure about the gears

 

[Darth Plasma]

I think there’s an issue with the EGR sensor because when I pull the vacuum line to the EGR valve I get no vaccum on either side and there’s no change in RPM’s or sound. I might try to drive it without the line to the EGR and see the difference