So not a third gen, but this seems to be the holy grail of TBI information so I would like to ask for some advice...

I have a '93 Suburban with a rebuilt 350 (origin not known) and a 4L60E tranny. 411 gears and 35" tires - not that that matters.

The engine runs fine down the road but runs (and smells) really rich at lights - hot or cold - to the point it sounds like it has an RV cam.

No EGR stuff left, rebuilt TBI, replaced ICS and TPS, Replaced fuel pump and fuel filter.

1) Could the MAP sensor be causing this?
2) What else can I check?

I have NO IDEA what the computer side of this rig is doing, the engine was taken from a donor vehicle before I got it.

Thanks, guys. I'm in a rut with this mess.

 

I should add that when I disassembled the TBI for the rebuild the IAC solenoid was WAY back in the bore (1/2" or so) and didn't look like it was even trying to control air flow. Spray pattern looks good and off-idle performance is fine (not great, but it's a heavy truck)

 

"Smelling" rich at idle is almost always due to misfire. If the engine is so lean that it misfires, it'll smell "rich".

There's the usual diagnostics: Cranking compression test, cylinder leakdown test, cylinder balance test.

Inspect the cap, rotor, plug wires and plugs. How old is the O2 sensor? Does the AIR system bleed air into the exhaust manifold screwing up the O2 sensor readings?

Verify no vacuum leaks, including an incorrect or defective PCV valve, and defective brake booster.

If the EGR stuff is gone, I'd be curious about the knock sensor and timing.

This could be a dozen (or more) different things, a scan tool would be a big help.

 

The AIR and PCV systems are gone and the ports are all capped off. The block just breathes through the air cleaner (minimal blow-by on the fresh engine). The brake booster was checked, but there is no telling on the knock sensor or the O2 sensor.

I guess I should replace them when funds allow and go from there. The truck only set a code twice the other day when on the interstate. Most of my driving is around town, and I haven't had time to check the codes yet.

Thank you for the informative reply!

 

It's foolish to disable the PCV system. Longer oil and engine life.

 

The PCV system was gone when I got the truck. I haven't looked into putting it back on yet as I have been focusing on getting the engine running properly first. Good advice though, thanks.

 

No AIR, no added oxygen to the cat converter = rich-smelling exhaust.

 

Unless the stock converter has been replaced with a 3-way cat. Then no need for the AIR system at all. Should be easy to reinstall the PCV system. A foot of 3/8" emissions hose and a PCV valve for your year truck should be all. Plugs into the only 3/8" barb on the front of the throttle body, labled "C" IIRC.

 

Make sue the map sensor vacuum hose is hooked up to the proper port, those ports do have a tendency to get plugged up w/ carbon. Measure the vacuum there, should be 18-21'' at idle.
Check the ign. timing & make sure it advances w/ you rev it up. This effects the engine to make vacuum.
Check the coolant temp sensor. You have to measure its resistence at different temps.
Check the grounds, esp the ones at the t stat housing & if there are ones at the back of the heads.

 

No cat on the truck, PO did a dual exhaust conversion.
I was curious about the coolant temp sensor and may just replace it. I'll redo the grounds first ( I like to do one thing at a time so I know what was wrong). Also, thanks for the PCV info - That will get done today.

The MAP sensor is hooked up and I have a vacuum gauge so I'll do that too. Not sure how to check the timing advance though - is it vacuum or electronic on these?

Thanks all!

 

E

 

check the spray pattern of the injectors. no drips and should be conical shape.