By Greg McConiga
Unintended consequences of port injection and reformulated gasoline.
Technology is a wonderful thing. A fix for one problem often only acts to create a new problem — one that doesn’t become apparent until the new process has been in place for a while. Take inlet system deposits, for example. In bygone years, we had a carburetor (remember those?) sitting on top of the engine Fuel was delivered above the throttle plates, which were awash in gasoline, one of the world’s great solvents. There were no carboned-up throttle plates and intake systems because they were washed clean by a swirling flow of fuel laden air. It was the same with throttle body injection systems.
Enter port fuel injection and with it dry inlet systems and straight gasoline directed right at the back of the intake valve. Throttle bodies began to coke shut with the remnants of condensed residual gases from EGR, PCV and a bit of combustion gas that migrated upward from cylinders with intake valves left standing open at shutdown.
Next came swirl- and tumble-control systems with shutters and valves in the intake that managed inlet airflow differently at various engine speeds and loads. We’re already seeing these systems arrive in our bays with components stuck and jammed with deposits, and customers complaining of a loss of power or fuel economy. Now, we’re getting early reports of a new problem on the horizon and we thought we’d better tell you about it so you can start thinking about how to fix it when it shows up at your door. Look for it regionally (due to local fuel formulation requirements), in warmer climates (our old nemesis, heat), and expect it to be a hard-to-find intermittent (welcome to automotive diagnostic hell!). It may suddenly appear in an area, then just as suddenly disappear as suspect fuel stocks are consumed.
Our phantom problem takes one of two forms: a crank-no-start condition with a higher-than-normal cranking speed (no compression), and a cylinder-swapping, rolling, random misfire, which will probably set a DTC. The root cause is carbon accumulation on valves and valve stems. This may be due to fuels, lubes and valve stem sealing systems, but the main problem is with fuels. Gasoline reformulation is ongoing in this country. Many standards are arbitrary; some are voluntary and most are regional. In general, fuel stocks are loosely overseen by the feds and more closely controlled at the state or local level.
With the exception of ethanol, nearly all of the old oxygenates have been pulled from the fuel supply. MTBE (methyl tertiary butyl ether) and methanol are gone, due to both health concerns and compatibility issues, but ethanol is here to stay. The environmentalists believe it will save the world, the agriculturists believe it will save the family farm, and the government is willing to subsidize it. I believe it’s a stop-gap measure as we move to alternative fuel sources over the next fifty years, but what do I know?
Crank, Shake, Pop, BOOM
The condition exhibits itself most dramatically when the engine is cold. Customer complaints will be along the lines of crank, no-start, or starts but runs roughly and seems to clear up after the vehicle builds heat. Diagnosis is relatively simple if the problem occurs for you, but catching it may require some co-operation between you and the customer — you may need the car for a couple of nights to pin it down. On cold start, listen for the high wavering starter sounds of low or varying compression and popping through the intake or exhaust system, which is indicative of a valve that’s not closing completely.
You may see flooded engine conditions requiring the replacement of plugs, and over-full crankcases that need to be drained. Note that an engine that is backfiring through the intake with an overly-rich crankcase is a bad thing! If the crankcase ventilation system fails to contain the backfire, you could light off the fumes in the crankcase resulting in the explosive removal of valve covers and oil pan. Don’t laugh. I saw it happen to one of my techs on an Astro van with the engine cover off. While he wasn’t hurt, his ears rang for a week, the explosion bent the leading and trailing edges of the valve covers up at about a 20 deg. angle in its rush to vent the pressure, and a couple of guys working nearby hit the deck.
If the engine will start, monitor engine misfires and listen for sounds of valve train separation. Abnormal clicking and clattering on the top end tells you that some of the valve train parts are no longer intimate. A good vacuum gauge will let you see intake pressure pulses that will help pinpoint the problem. If you still own an ignition oscilloscope that shows secondary ignition patterns, you can identify slow or no-close valves by the presence of turbulence in the spark line. Note that many late model engine designs exhibit turbulent patterns, so you’ll have to study several cylinders to identify the standouts. In a nutshell, compression pressure trying to leak past the valve will create a wind-tunnel effect at the plug, much like trying to “blow out” the spark. You’ll see a jagged spark line with shortened spark duration. Obviously, this technique won’t work with multi-strike systems.
Once you’ve identified the condition, you’ll next need to confirm that the valve train is still intact. It’s not unheard-of that hydraulic lash assemblies, pushrods or lifters get tossed, or valves become bent during this kind of failure necessitating major engine repairs.
I looked for bulletins on this among several manufacturers. While my search was by no means exhaustive, it seems that the problem is in an early stage with relatively few cases noted. I found a preliminary information bulletin at General Motors dated 11/09/2006 that describes the condition, as well as a couple of other vague references to carbon-related problems on other websites, but it looks like this kind of trouble is relatively rare at this point. According to GM, the fix involves checking for obvious secondary damage to the valve train, adding GM Fuel System Treatment PLUS PN 88861011 or AC-Delco PN88861013 to the fuel tank, filling up with a Top Tier fuel (see list below) and using GM Top Engine Cleaner to complete the job. The bulletin (PIP3146B) also states that it may be necessary to disassemble the engine and mechanically clean valves and valve guides to achieve a successful repair. Sounds to me like prevention is the order of the day.
Don’t Let it Get Started
Top Tier fuels contain bolstered additive packages that were designed by the four-manufacturer consortium of GM, BMW, Honda and Toyota. Rather than accept the “Lowest Additive Concentration” set by the EPA (your tax dollars at work again), these automakers set their own standards for fuel system deposit control beginning in May of 2004 and labeled the mix Top Tier Detergent Gasoline. According to the consortium, the current EPA minimum doesn’t go far enough to ensure optimal engine performance. Minimum additive and detergent performance standards first established by EPA in 1995 have actually been reduced by up to 50% in today’s fuels by fuel marketers, and the ability of a vehicle to maintain stringent Tier 2 emission standards has been hampered by the subsequent formation of deposits. From the manufacturers’ point of view, this has a negative impact on consumer satisfaction and confidence, as well as affecting vehicle pass rates at emissions inspection stations. Hence, you should suggest that your customers fill up Top Tier stations, such as:
■ Entec Stations
■ MFA Oil Company
■ Kwik Trip/Kwik Star
■ The Somerset Refinery, Inc.
■ Aloha Petroleum
■ Tri-Par Oil Company
Or, for more information go to www.toptiergas.com/index.html