Hey guys,

I have a 1989 GMC Suburban 4x4 with a TBI 350 that I am having some issues with. I've had it since January of 2010 and it has always ran very well, until about a month ago.

I stopped at a red light, and it quit on me. When I restarted, it was popping, hesitating to the point where it was nearly undriveable and kept quitting until I got her home. When I got her there, it wouldn't start at all.

After some troubleshooting, I replaced the fuel pump, in tank strainer, and fuel filter. After I was done with that, the truck started right up and idled, but still didn't run good. I had never gave it a tune-up (previous owner said he did right before he sold it to me) so I decided to give it a full tune-up. New cap, rotor, plugs, wires, ignition module, coil and all new vacuum lines and a new serp belt, fresh oil and filter.

The truck ran a lot better but still had a hesitation coming off idle, and had a miss when warm at idle and about 1000 to 1500 rpm. Checked the timing, was spot on at 0 with the electronic advance wire disconnected.

I figured what the heck, and replaced the CTS, 02 sensor and MAP sensor, still the same.

At this point, I took it to a dealer and had them take a look. They said the Dizzy was on its last straws, and that it would need a new cat. converter. I took it up to the exhaust shop and had an entire 3" single exhaust system put on, minus the cat with a 24" glasspack. Its almost too loud, but my kids love it!

I also replaced the distributor, but the problem was still there. Same issue, hesitation right after idle, low idle in gear, lack of power and very slight black smoke right around 1000-1500 RPM (same time I see the smoke), especially when cold. When the truck warms up, it has a slight miss at idle.

I have checked the Vacuum, which remains steady, drops to 0 when I crack the throttle. I checked the TPS which shows a good range of motion, starting at .61V and goes nice and steady up too about 4.5V WOT.

I took it to another shop, not a dealer, but a shop that I was told does very good work, and they said that one of the fuel injectors was leaky and dripping, so I bought 2 new injectors, and the Fuel Pressure Regulator. Not even a slight change. Took it back, and they said it was probably the EGR, they had done a vacuum test on it, and it tested ok, but it could be that it was carboned up and not closing all the way.

Bought a new EGR valve, and it was carboned up, but not much, and the passages looked pretty clear. I cleaned it all up, installed the new EGR, checked the timing once again, and still have the same issue.

I have checked the timing numerous times, and it is always rock steady, I have replaced or tested about every part, and I am even to the point of checking the new parts I have installed.

The engine doesn't tick, knock, or make any other crazy sounds. 3 trips to the shop, and no dice. Anyone have any ideas?? There had never been any codes, but the SES light comes on with the key so I know its working. Ive tried pulling codes, but only get 12, which tells me the diagnostics is working.

Thanks! Sorry for the long post!
Ryan

 

Have you checked the intake and around the throttle body for a vaccum leak? Also I had a TBI that was acting similar and the throttle body itself (actually the shaft that the throttle plates ride on was worn out). You have definitely thrown a lot of parts at it and when you do figure it out that truck is going to be as close to new as you can find. It would be nice to find a buddy with a good running TBI truck and swap the throttle bodies just to eliminate that as a cause. There is also a pressure regulator inside the TBI unit that might be messing with you.

 

haven't checked the throttle plates.....but I may try to find a junk yard unit to swap out or like you said, a buddy with a good running truck to swap stuff.

I have replaced the fuel pressure regulator, but I am not going to rule that out, as I had to readjust it twice because it kept leaking. I may redo it once again with a new part and go from there.

Thanks for the advice!
Ryan

 

I have an appointment on Monday for a 3rd shop to check the fuel pressure, and everything else associated with the fuel system. Basically to double check my work on it. I have no garage and it is getting a heck of a lot colder lately, and they are going to charge me 25 bucks. Not having to be out in the cold is worth 25 bucks to me!
thanks
Ryan

 

By chance did you pull the throttle body off and clean all the passage ways. My father and I discovered that even after we replaced the EGR that the passage ways were carboned up too. Almost to the point of being stopped up. After cleaning his and mine both 1990 5.7s they ran much better. Hope this might help.

 

I will have to try that if they can't find anything wrong in the shop again. I am heading over there here in just a few minutes so they can check it out.

Thanks for the advice!
Ryan

 

Also replace the gasket with a new 1.

 

Got it back from the shop today, and they told me that my exhaust is too big, causing problems with the EGR system. He said that If I add a catalytic converter and a regular muffler, instead of a glasspack, that it should cure the problem. They checked fuel pressure, cylinder compression etc, and everything checks out. So....do I drop money on a new cat and muffler, or do some more troubleshooting?? He said they messed with the timing a little bit, and it does seem to run better, but still not 100%.

Is there a way to test the exhaust theory without redoing my whole exhaust again?? can I try to restrict the exhaust somehow to see if it helps?? Thanks guys!
Ryan

 

You're running 3" right? I had 3" with no cats that then split into 2.25" duals and didn't have a problem on my 92 TBI 350

 

Yeah I think it is time to get a 2nd opinion. Did your truck start messing up right after the exhaust install?