: Randomly Running Extremely Rich

12-12-09, 03:26 PM
Hi, I had a new problem develop a few months ago on the 94 STS. The car will randomly run extremely rich. Idle gets rough, exhaust becomes blackens up. It's a completely random event. Does it sometimes while warming up, sometimes when driving, sometimes while sitting at a light. It usually lasts about 10 minutes then clears up and drives normal. Anything under load is not a problem as the engine burns up the extra fuel. I checked the fuel pressure regulator. 40psi at idle and it holds 20" of vacuum all day long. The engine is not throwing any codes. At first I thought it was a missing on cylinder, and changed out the module and all the coils. Had no effect. Will the engine through a code for an engine mis? Anyone ever have an injector hang open??? I know they can leak closed. The car has 330K so it's due for new injectors. The only other thing to add is that sometimes instead of black exhaust, it will give off a blue smoke screen effect (very noticeable), and there is still a strong smell of fuel. Open to all suggestions, Thank you, Steve

12-18-09, 11:12 AM
My bet is on one or more fuel injectors - but replace them all at the same time so you wind up with equal flow rates across the board.

The blue smoke is oil - how much does your engine use, and what kind ? Shift to a HD Fleet or Marine dino 10W-30 oil - Shell Rotella, Chevron DELO, Pennzoil Long Life - all have a high-load ZDDP and anti foam package which so-called "Starburst Energy Conserving" oils do not have.

12-23-09, 12:54 PM
Sorry for the late response. Tis the season for being busy. I will replace all the injectors. I was going to anyways. As for oil. I am in Canada so I usually run Esso XD3. (15w40 synthetic) It's like Rotella oil better. :) Canadian oil not sold in California so it has all the good stuff in it. Thank you, Steve

12-29-09, 09:02 AM
Strange that the fault isn't causing any codes? I had a similar problem years ago and it turned out to be a bad sensor (MAP or MAF, can't remember which). One thing you'll also want to probably do is relplace the oxygen sensor(s), as they get ruined by the carbon buildup. Operating like that (extremely rich) for extended periods can also ruin the catalytic converter - best to get it fixed pronto!

12-29-09, 11:48 AM
15W-40 is awfully heavy oil for Canadian use.........look at the Fleet and Marine 10W-30 offerings from Chevron (DELO), Pennzoil (Long Life), and Shell (Rotella).

12-29-09, 11:33 PM
arnt you supposed to have 5w30 in it??? 15w-40 is diesel oil......and i wouldnt even run that in a diesel in the cold.

12-30-09, 09:42 AM
Actually many diesels, both large and small, call for for 15W-40 oils. The Caterpillar 3208 series of truck and marine V-8 (NA and turbo) is spec'd for it year-round. We use Pennzoil 15W-40 Long Life truck oil in Olds 455 marine engine installations and have exceptional service and oil life as well as clean lab tests, BUT a Northstar is a different matter altogether - the tolerances in that engine are definitely NOT in the 15W-40 playbook.

Based on Jake's work with several breeds of Northstar and my work with Olds engines, I would hazard a recommendation that the 1999 and earlier Northstar (flat tappet hydraulic cam follower engines) should now use a truck or fleet 10W-30 oil due to their higher ZDDP anti-scuff additive package which was removed from "starburst" - "energy conserving" automobile rated oils a few years ago as an EPA requirement.