Are TBI 350’s just this sluggish?

[BradHSo]

Do they use a similar spider injector?

iNope I believe they are a traditional MPFI. But I could be wrong

 

[White96k2500]

I don’t believe so, but they are stricken with the common leak down problem, if it sits for a awhile it’ll just crank and crank and crank, then blow black smoke. Plus the MPGs took a turn for the worse around 6-8. It’s a pretty well know issue for the vortec 7400’s

Welcome from Asheboro NC! Theres quite a few Of us from NC on here. My truck (5.7 vortec) has the leak down problem I believe, after i drive it and cut it off to get gas or something and go to crank it rolls and rolls and act’s like it’s not gonna start then it starts and it runs fine lol. I really dread doing the injectors on it

 

[stutaeng]

Do they use a similar spider injector?

No spider injectors on the 7.4. It has individual injectors on an external fuel rail like any modern engine. I've never owned with one and was aware that they had issues, but recall seeing someone here that the aftermarket injectors solves this problem. Bosch injectors, I think?

At least you can replace them without pulling the intake manifold plenum like the 4.3/5.0/5.7.

I'll just add to the OP to check vacuum hoses, as some tend to dry out and crack and go unnoticed. Maybe someone already brought it up.

 

[SUBURBAN5]

Wow that's wierd. Wonder why they did that.. guess for more fuel volume?

 

[BradHSo]

No spider injectors on the 7.4. It has individual injectors on an external fuel rail like any modern engine. I've never owned with one and was aware that they had issues, but recall seeing someone here that the aftermarket injectors solves this problem. Bosch injectors, I think?

At least you can replace them without pulling the intake manifold plenum like the 4.3/5.0/5.7.

I'll just add to the OP to check vacuum hoses, as some tend to dry out and crack and go unnoticed. Maybe someone already brought it up.

Cool, I wasn’t familiar with that term, but thought it was a normal MPFI with two rails. I’ve sprayed ether around the vacuum lines after I replaced them and didn’t get a raise in RPM so I think I’m good. Now the 454 needs a lot of work, but that’s different thread lol

Yes when ever I upgrade the injectors that is what I will be going to the, the latest generation of Bosch injectors.

 

[L31MaxExpress]

Something is definately up. With some bolt-ons my stock cam, stock 810 swirly head 350 TBI was strong from off-idle to 5,000+ rpm. Everybody saying these heads die at 3,500 has not driven one with headers, decent exhaust and a decent chip tune. This was how mine ran with a stock 8,600+ GVw long block. Factory rated it at 180 hp and 300 tq at the crank. With bolt-ons made 200 hp and 300 tq at the wheels. 2nd gear roll on at about 30 mph. When I lifted it was rolling a out 75 mph.

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[Pinger]

Fuel pressure was 8-9 at idle cold and after it warmed up it dropped to a steady 7, my fuel filter was slapped fuel of black and red gunk. I unplugged the tan and black wire then checked the timing and holy crap was it retarded, it was so far to the right that it was off the timing marker.I re timed and changed the filter, I think I’m making progress as the truck feels a lot better and doesn’t hesitate off idle. Will be ordering a fuel pump next and changing the ICM and coil as I listened to PlayingwithTbi’s advice and misted it with water and it immediately ran like crap.
Thanks for everyone’s help!

Years ago I bought an old W123 Mercedes 200 and it was gutless. Checked the timing and it was timed to fire at TDC. Re-setting to its correct timing perked it up no end. Still wasn't quick but at least it could actually move itself.

 

[DerekTheGreat]

I've been driving 350 TBI trucks for quite awhile now. Like other said, verify the basics. My wife's '92 C1500 350 five speed truck with 3.42's doesn't seem to have the grunt mine has. Need to look into why but her engine is slimy right around where the intake meets the heads, I suspect those gaskets are toast.

 

[someotherguy]

Fuel pressure was 8-9 at idle cold and after it warmed up it dropped to a steady 7, my fuel filter was slapped fuel of black and red gunk. I unplugged the tan and black wire then checked the timing and holy crap was it retarded, it was so far to the right that it was off the timing marker. I re timed and changed the filter, I think I’m making progress as the truck feels a lot better and doesn’t hesitate off idle. Will be ordering a fuel pump next and changing the ICM and coil as I listened to PlayingwithTbi’s advice and misted it with water and it immediately ran like crap.
Thanks for everyone’s help!

Great progress. The black gunk might be pump guts, so a new pump may be on your list soon. What's the pressure now you've replaced the filter? Spec is 9~12 psi but anything less than 10 and I'm giving it the side-eye.

Timing corrected should make a very obvious difference if it was retarded, though fuel pressure will hold you back if it's still low. I think a lot of shadetree type guys don't know about the tan/black wire and they just time it "by ear" ...

If your CTS looks old (your engine has two temp sensors, the one next to the thermostat is the CTS - input to the computer) you may just want to replace it. They often go bad gradually so you don't notice until they get really bad. As they go bad their resistance increases, which the PCM interprets as colder coolant temperature. The colder the coolant, the richer the fuel mixture. They eventually go completely ****-up and will read so cold the mixture will richen to the point it will foul your plugs and stall the engine.

On the coil, be sure to skip any "performance" coils; no actual performance improvement and often far shorter lifespan than OEM.

Richard

 

[someotherguy]

I don’t believe so, but they are stricken with the common leak down problem, if it sits for a awhile it’ll just crank and crank and crank, then blow black smoke. Plus the MPGs took a turn for the worse around 6-8. It’s a pretty well know issue for the vortec 7400’s

Yep, super typical behavior of leaking injectors and bad fuel pressure regulator on the Vortec 7.4. Replace 'em with the Bosch pieces and a new FPR, be sure to replace the vacuum line to the FPR while you're at it and be sure the line is fuel/vapor rated so it will live.

It's a little bit of work but really not all that bad. What's bad is how much the injectors cost..!

Quite a few years ago I did that injector replacement on my 3500HD. Pictures and a couple tips and tricks at - http://www.someotherplace.com/bb/proj/35hd.html - scroll down to the entry for 02-20-11. Take special note of breaking the EGR tube coupling nut loose. The "backup nut" portion of the fitting into the intake is very shallow; most wrenches large enough to fit the nut size are so wide they interfere with loosening the coupling nut. Channel-Lock makes some adjustable wrenches they call "extra slim jaw" that work perfect for this job.

Richard