89 burban 350tbi runs rough

[Chaz]

I purchased an 89 Suburban V2500 4x4 about 4 month ago. Its got about a 6 inch lift on 35" BFG,s 400 tranny. I love this truck but the 350 tbi motor is starting to drive me nuts. When I got it it was idle surging. Had a bad intake manifold gasket. I swapped out the manifold for an Edelbrock performer tbi and a holley 670 tbi unit. I also replaced cap rotor plugs wires coil etc,,,Its been running really good for about 4 months. Now I have problems again. It started running rough after I replaced the drivers side front power window motor and regulator. It just started idling really rough,,,not surging like before. I got pissed and took it to a mechanic. The truck barely made it in to his shop on its own power and died. Mech said the rotor in the cap was burnt,,,he replaced cap and rotor,,,and the plugs,,,he showed me the cyl #1 plug was burnt black with carbon,,,,all the other plugs look nice and grey. He said he compression tested the cylenders and thy all check out good. Well now the truck runs a lot better. But while in park it idles good. In drive or with parking brake on it sometimes runs good and sometimes it starts bogging down like theres a miss. And the more I drive it the worse it gets. Sometimes it runs so bad it just dies. If anyone has any idea how to fix this I'd really appreciat it. Thanks.

 

[Jims86]

I purchased an 89 Suburban V2500 4x4 about 4 month ago. Its got about a 6 inch lift on 35" BFG,s 400 tranny. I love this truck but the 350 tbi motor is starting to drive me nuts. When I got it it was idle surging. Had a bad intake manifold gasket. I swapped out the manifold for an Edelbrock performer tbi and a holley 670 tbi unit. I also replaced cap rotor plugs wires coil etc,,,Its been running really good for about 4 months. Now I have problems again. It started running rough after I replaced the drivers side front power window motor and regulator. It just started idling really rough,,,not surging like before. I got pissed and took it to a mechanic. The truck barely made it in to his shop on its own power and died. Mech said the rotor in the cap was burnt,,,he replaced cap and rotor,,,and the plugs,,,he showed me the cyl #1 plug was burnt black with carbon,,,,all the other plugs look nice and grey. He said he compression tested the cylenders and thy all check out good. Well now the truck runs a lot better. But while in park it idles good. In drive or with parking brake on it sometimes runs good and sometimes it starts bogging down like theres a miss. And the more I drive it the worse it gets. Sometimes it runs so bad it just dies. If anyone has any idea how to fix this I'd really appreciat it. Thanks.

If you still have the original throttle body, throw it back on and see what happens. Did the Holly throttle body come with a chip?
Do you know how to pull codes from the computer?
Post pics of the TBI and manifold so we have some porn to look at.

 

[Chaz]

I chucked the orig tbi,,,the mechanic told me it needed a rebuild,,,,the holley did not come with a chip,,,,holley said it was a direct replacement part so it's smog legal,,,it came with a thick gasket that made it fit the mainfold even the holes are smaller than the new tbi,,,the trucks not throwing any codes and theres no check engine light on,,,,the edelbrock mainfold is stock replacement also,,,,its the same as a stock mainfold,,,there was no performance improvement at all which was a surprise for me,,,,maybe cuz its a tbi engine,,,ill post some pics whn i can upload em to my computer,,,,

 

[HotRodPC]

Dude has my 2nd Choice Truck. Except, I'd be converting it to 454 Vortec/4L80-E/NP205 and Dana 60 front.. He's even already got the 6in lift and 35in tires. I bet it gray interior too !!!

 

[HotRodPC]

I chucked the orig tbi,,,the mechanic told me it needed a rebuild,,,,the holley did not come with a chip,,,,holley said it was a direct replacement part so it's smog legal,,,it came with a thick gasket that made it fit the mainfold even the holes are smaller than the new tbi,,,the trucks not throwing any codes and theres no check engine light on,,,,the edelbrock mainfold is stock replacement also,,,,its the same as a stock mainfold,,,there was no performance improvement at all which was a surprise for me,,,,maybe cuz its a tbi engine,,,ill post some pics whn i can upload em to my computer,,,,

Well, you got the right guy on this one already Chaz. Seems we have a guru in about every field on these trucks. Jims the one for the TBI issues, so if noone else posts up, that's why. You'll get it worked out with help from here.

 

[Chaz]

Its orig all blue with blue interior, ya its great when its running good but im startin to hate the tbi motor,,,,its also got around 4.80 gears,,,,im at 3000 rpm at 65 mph,,,,so ive been thinkin bout goin to a 4 spd tranny,,,,really need it on the hwy,,,,power is good though

 

[Chaz]

That would be great man,,,,,any help I can get would be awesome,,,,if I dint have to pass a smog ck i chuck the whole intake and bolt on a carb lol,,,,,

 

[HotRodPC]

Its orig all blue with blue interior, ya its great when its running good but im startin to hate the tbi motor,,,,its also got around 4.80 gears,,,,im at 3000 rpm at 65 mph,,,,so ive been thinkin bout goin to a 4 spd tranny,,,,really need it on the hwy,,,,power is good though

4.88's are a great gear choice with 35's. Being that you're 3/4 ton, and it'll be a bit tough to find cuz they get sucked up real fast for upgrades, but a 91 model with a 4L80-E/NP205. I think you have to grab the ECM too so that you have the trans controller provision. Can't go up to the 92 model, cuz GM swapped to Right side drop on the Tcase. Of course you could get the ECM and the 4L80-E out of the later models, then deal with the Tcase issue seperately. But yes, you can get it to a 4 speed Auto with overdrive with the right OE parts.

 

[Chaz]

Pics of tbi and manifold,,,not really porn though lol,,

 

[HotRodPC]

,not really porn though lol,,

It's not??? Those pics don't make your sticker peck out??? hmmm, you might not be a good fit here after all.

 

[Chaz]

I guess im not really a tbi fan,,,,i dont know how gm could only get 200hp out of a 350 v8,,,its supposed to have heads that make more low end torque right,,,,i hav a 95 burban with a 350tbi and its such a pig,,,,,but i liked the suburban so much (4 kids) that i bought the 89,,,im just hatin that thing right now cuz its pissin me off,,,,now if it was a big block or a built small block id be more excited but im not feelin it right now,,,,gotta tell myself its not a prius lol

 

[Jims86]

Ok... 3 things. go ahead and swap the injector plugs...Green and white is supposed to be on the drivers side, per factory practice. I swapped mine one time, to see what happens....ran like ****.
Also, check the vacuum line off the back of the throttle body going to the MAP sensor, and make sure its not cracked.
When was the fuel filter done?
Power on these engines is pretty good for what they were designed for. Its all in the cam, really...its a trade off really. Quick, short duration, means low end grunt, where you want it in a truck. Bigger cams usually mean torque up higher, wher the HP is also easier to make.
Newer VVT technology, coupled with tall, narrow intake runners(LSx) give you the best of both worlds.

 

[Jims86]

Oh yeah...Go around and give all the intake, EGR, and throttle body bolts a little snug, check the vacuum fitting for the brake booster-intake manifold line..
And that Coil MAY be a problem when passing inspection, unless you have a CARB EO number for it...A friend here in the Central Valley had his burb fail, due to the aftermarket coil.
Check the ground nut on the thermostat housing.
And an FYI about that particular throttle body, Keep an ey on it up around the top of the injectors, they have been known to leak, and in some instances, have lead to carbecue's.

 

[HotRodPC]

Yepper, V V T (Variable Valve Timing) is the **** !!! Actually give you the low end econo grunt, but when to open up some haul ass, the lift and duration get taller and longer like a big cam, so now you got the hp you're looking for and higher rpm torque.

 

[89Suburban]

Try unhooking the EGR valve...