Have changes in injector designs and gasoline additive packages made injector cleaning obsolete? Or, to put it another way, can a professional repair shop justify selling this service today?

It depends on whom you ask. Opinions vary all over the map. The oil companies will tell you that using their latest gasoline formulations eliminates the problem of clogged injectors, while other authorities say it's in the nature of liquid hydrocarbons to create deposits in a hot environment regardless of the cleaning solvents added. And carmakers claim that their current injector designs are just about immune to clogging, but there are reports from the field that even deposit-resistant injectors get plugged.

The mechanism
So what's the truth? As with most other things in life, there are no easy, black-or-white answers. The best I can do is lay out all the info I've gathered and let you decide how it affects you. I'll start this exploration with the basics of deposit formation. Greg McConiga, a former NAPA/ASE Technician of the Year, has done a great deal of research on the subject. I'll quote what he told me about it:

"Gasoline is composed of several hundred compounds, two families of which carry a large portion of the guilt for injector problems: olefins and diolefins. By themselves, they won't cause injector deposits. They must be accompanied by "polar materials" (alkanes, alkylbenzenes and alkyl derivatives, etc.).

"But there are lots of other factors to consider. Injector soak time, for instance, which is one of the biggest contributors. The worst case scenario would be 15 minutes of running followed by 45 minutes of hot soak -- just what an around-town driver does. Deposits don't form while fuel is flowing, only when it stops. Then there's fuel system configuration and injector tip temperature. Any closely-contained or turbocharged engine will form deposits rapidly due to high injector tip temperatures. Geographical considerations come into play also. The injector failure rate is higher where it's hot and dry than in more moderate climates. Heat is the obvious link.

"Another factor is that deposits are promoted by EGR and PCV gases present in the intake passages at shutdown, which condense onto sensitive surfaces. In fact, this appears to be a big part of the mechanism that plugs injectors. The olefins, diolefins, and polar ends leave a sticky gum-like residue as the light fractions evaporate, and this can become very tenacious if baked on over several hundred cycles. Under high magnification, these deposits appear as small, round, black nodules.

"We've all seen the effects of injector fouling (whether we recognized it as such is another question). Probably the most common complaints are rough running, hesitation and stumbling on light acceleration, as well as dramatic increases in emissions. An 8% average injector restriction can cause hydrocarbons to rise 26%, carbon monoxide to go up 16%, and fuel economy to drop 2%. This is because while in closed loop, the system will try to compensate for a lean condition (as observed in the exhaust manifold) by lengthening the pulse width for all the injectors. Look at the block learn and integrator numbers on a scan tool.

"Frequently at our shop we see cases of severe driveability problems caused by injector deposits. Fortunately, almost all injectors clean up with the use of commercially-available cleaning systems and chemicals, and will remain clean with the use of a good detergent fuel. According to an MVMA gasoline survey, regular grades of gasoline measured 40% olefins by volume as opposed to 20% for premium.

"Even though redesigned injectors hold out hope for a big reduction in plugging, and the car makers are making changes in cooling, EGR, and PCV systems, engines with deposit-prone designs will be on the road for many years to come."

Thus spake McConiga.

Ivory tower?
Speaking of recent injector design improvements, I should mention AC-Rochester's recommendations for its Multec units, which appeared in '87. The company's service literature states:

"Questions from the field have been raised as to whether Multec Top Feed PFI injectors can or should be cleaned using GM Fuel Injection Cleaner or other chemicals introduced through the fuel rail pressure connection. The AC Rochester-produced Multec PFI injector is designed with a self-cleaning ball-type valve and fuel flow director plate. Varnish build-up is eliminated due to the spray tip that shields the director plate from fuel particulates that are present in the intake manifold. Although cleaning, if done according to the cleaner manufacturer's instructions, will not damage the Multec injectors, it will not improve their performance, either."

And Lucas, which manufactures its cleverly-conceived disk-type injectors in South Carolina, is of the same mind. Because the disk and orifices are almost halfway up inside the unit, there's much less chance of clogging than with the traditional pintle-type. By the way, these are approved replacements for GM and others, and have been adopted as O.E. for various BMW's, SAAB's, Jaguars, etc.

Get real
But does the real-world experience of those in the trenches of auto repair justify the practice? Not in every case. Bob Peppin, New Hampshire shop owner and 1982 Technician of the Year, told me, "I have an aerosol set-up. When I use it, I can sometimes hear a little difference in the way the injectors sound. But I've weighed the cost against the benefits, and the income against the risks involved. You're working in a hot engine compartment with a pressurized can of highly flammable solvent. What happens if a fitting blows or something? And you could ruin a paint job. The exhaust system gets cherry red, so if those parts are marginal you could be blamed for a problem there, too.

"I've been in business for 15 years, and I can't honestly tell you that I've ever seen a plugged injector. If I replace one injector a year, it's a lot. I wouldn't stock them, that's for sure. Maybe it's a regional thing -- the cool weather up here might have something to do with it. We add a can of cleaner to the gas tank when we do a tune up, and I recommend that customers fill up periodically with brand-name super. We don't have to do injector cleaning. There's plenty of needed work to keep us busy."

Mitch Schneider, California shop owner and popular MOTOR SERVICE magazine columnist, is also not entirely thrilled with the potential of injector cleaning. He said, "We do the service because people want it, but we've seen very few instances where we've actually fixed a car by doing injector cleaning. Occasionally, we have seen dramatic results on European cars with CIS."

Middle of the road
Alan Keyes, New York shop owner and 1988 Technician of the Year, occupies the middle ground. "We're not cleaning as many as we used to," he said. "We're just not getting as many problems. One thing we do is install a bottle of concentrated fuel injection cleaning solvent in the tank. We use Chevron Textron, which has been approved by lots of carmakers, and we find that it really works.

"We judge whether or not injector cleaning is needed on the basis of four-gas analysis, and we take the sample ahead of the cat -- we drill a hole and put a pipe plug in it. But most of the driveability problems we see aren't from clogged injectors. We see more fuel pump inefficiency or restricted strainer socks in the gas tank causing fuel volume problems. We've been replacing a lot of pumps and strainer socks, whereas we only replace about five or six injectors a year on the average.

"On the other hand, I don't think the job of cleaning injectors is going away. We started with a bulk cleaning system about three years ago, but we switched to the aerosol type for convenience and because it's an easier sell."

Andy Balmuth, well-known fuel injection trainer, said,

"I see injector cleaning as a preventative maintenance procedure, or as part of a major tune. As far as determining when it's needed other than as maintenance, it depends on the specific complaint. Off-idle stumble and any kind of rough running are typical problems that can be caused by partially clogged injectors. Using a pressure gauge and one of those 'buzz boxes' that pulse the injectors one at a time is a good test. The set-up that uses a sight glass instead of a pressure gauge is even more accurate."

Aftermarket view
The tech services manager of a major injection solvent and cleaning kit manufacturer gave me his perspective on the future of this job: "I still see a viable need for this service even on the newer systems," he said. "If anything, I think there'll be an increase because of environmental concerns and more emissions testing."

"One factor is that an SAE fuels and lubricants committee has stated that continued use of EC (Emission Control) gasolines that contain an oxygenate like MTBE have been scientifically proven to promote deposit formation. In Phoenix, for example, there was a program to use this type of gasoline, but there were many complaints of driveability problems caused by deposits in injectors and on the valves. And that type of gasoline will probably become more prevalent.

"It's basic physics. If you push fuel through an orifice in a hot environment, you're going to get coking. According to information I've been given orally by O.E.M. sources, the new style injectors may take longer to clog, but it will happen. I feel as though there is always going to be a need to clean injectors and intake valves because of engine designs, fuel composition, and driving habits." His company must go along with that opinion because it has spent a great deal of R&D money to improve its injection cleaning products.

The last time I talked to McConiga on this subject, he told me, "We're still cleaning injectors because there's no indication that it doesn't work. We recommend cleaning every 30,000 miles. No matter what the oil companies say about their new gasoline formulas, or what the manufacturers say about deposit-resistant injectors, we still see that 3-4% variation that can cause driveability and idle problems. Deposits form because of the composition of gasoline itself, and all that stuff in the manifold from PCV, EGR and fuel is looking for a place to condense."