One doesn't need to search far when looking for pattern failures to find many problems that are common to specific fuel injected engines. The "analysis" part of our businesses brings in these vehicles on a daily basis.
Another method of finding these vehicles is to use iATN (International Automotive Technicians Network). Members can search the network's archives to find the most common problematic vehicles by make, model and engine.
I have found that injector problems most often are brought on by:
1. Design
Though not by intent, some injector units are just very poorly designed overall. Seals, windings and other component parts simply fail. Incorrect materials may have been used that do not hold up to the heat and rigors of underhood life.
In a perfect world, manufacturers quickly become aware of these situations and either recall, repair or replace these units early on in the production of an automobile. Yet even with recalls, thousands of units are still left out there for service shops to contend with and repair.
The GM Multec unit seems to have the record in the failure department with many units having shorted coils (low resistance) causing a rough-running engine and no-starts, and may even cause PCM injector drivers to fail requiring total PCM replacement.
Much has been said in regard to these types of failures and these units, and often, cleaners and fuel are blamed. But if the design were perfect, the cleaners and fuel would never get into these coils to begin with. Note that many units in production today using the same fuels and cleaners don't exhibit this problem.
2. Fuel System Contamination
Contamination will always be a factor when servicing a fuel injection unit. Contaminants often find their way into the fuel tank from a fuel-dispensing unit at a filling station.
3. System Service or Mishandling
Mishandling comes into play when the system is opened for replacement or service and is allowed to sit in the service shop (or wrecking yard) for an extended length of time. Special care must be taken when servicing these units. Seal all areas, use only clean replacement fuel when servicing and properly dispose of contaminated fuel.
After servicing more than 40,000 units, I would have to say that the majority of the problems I've seen have been simply contamination. Contamination comes from a variety of areas including dirty fuels and fuel deposits. Although the fuel quality is very much better today than in the early 1980s, there are still problems with some fuel contamination and fuel deposits. Mostly, I call these issues "neighborhood related," meaning some areas of the country have more service problems than others.
Contamination can be fixed in many cases on the vehicle by using one of the many two-line fuel system flush units on the market today or an off-car cleaning system with the reverse-flush ultrasonic systems.
Due to continued contamination problems throughout the county, filtration designs are continually being improved. In fact, some OEMs have enhanced the filtration to twice of what it was just a short time ago. Also, the latest high-pressure "gerotor" pumps require tighter filtration to prevent a short life cycle. To protect these pumps, some OEMs have tightened their overall filtration
With the latest offerings of returnless fuel systems, filter service is not suggested as a separate service item like before, most use the filter unit as a non-replacement item. These units require a total fuel pump modular replacement with regulator and filtration built in. Since this is a direct emission item, look for more and more of these units to be added to the next generations of automobiles.
Although the final injector filter is approximately 10 micron, some particles of dirt, rust, etc. still get into the injector unit itself. A dirty injector will cause the pintle to hang up or drag. This drag may cause the vehicle to start hard, run rough or not start at all (especially when cold).
Use the inductive low current probe, which shows the injector opening point and pintle position, to determine if this drag is causing a problem. A scope waveform from the current probe confirms injector coil condition and actual pintle lift in a very quick non-intrusive inductive hookup. This has got to be one of the best tips of the day for service technicians.
Shorted Injector Coils
Some engines use a "pattern failure" injector, meaning that the injector is more likely to fail than others. The GM Multec Injectors fall into this area as they often have shorted injector coils with a lower-than-normal working resistance. This causes a very high current draw, which may lead to a no-start, rough-running engine or a total PCM failure.
We have determined that current testing is required to test these units, as ohm testing doesn't load the coil enough to detect a marginal injector bobbin or coil failure. GM suggests the Kent Moore tool # J-39021 available through OTC as # 3396 unit, and I suggest the use of a current probe with the tester in lieu of the digital voltage readings suggested.
By using the current probe we can observe the current flow through the injector coil for a full five seconds under actual loaded conditions. I feel as if the digital voltmeter is somewhat unstable doing this test and prefer the current waveform.
A current probe is used around the power leads to the tool, and reads actual loaded current on each test. The tool limits this current, but the stability of the waveform may be monitored.
On-car injector coil testing has been greatly improved with the advent of the low current probe offered by many aftermarket companies. The current waveform for most injectors may be viewed from the actual injector harness, the engine harness and, in many cases, the injector power fuse.
CPI System No-Start
Another "pattern failure" unit has been the GM 4.3 Vortec with the Central Port Injection (CPI) unit. The CPI unit is very similar to the old "dribble" system of the late 1950s used on the Corvettes. The system is mounted under the intake plenum and uses a single injector with six spray holes feeding a pod with six lines and poppetts.
This CPI unit operates the main "maxi" injector at approximately 60 psi, and fires all injector lines with poppetts at the same time requiring approximately 43 psi to release final fuel spray.
This unit has been plagued with sticking poppetts, leaking fuel pressure regulator, leaking fuel supply lines (under plenum) and a high fuel pump failure rate.
GM lists a fuel pressure specification of 54 to 64 psi as being the correct pressure for the 4.3L V6 application. Note: The key is on, and the engine is off. Many techs have been somewhat fooled with a no-start at 56-57 psi. This system MUST have 58-60 psi to operate correctly. The reason is the actual volume of fuel at different fuel pressure settings!
Note that at 56 psi, the unit sprays approximately 20 mils of fuel. When at the correct pressure of 60 psi, the unit sprays 28 mils. This is a huge difference in volume (28%). Repair parts are not available for this impediment, and technicians must replace the entire unit with a new unit or reconditioned assemblage.
The EGR system on this engine has also been somewhat of a pattern failure, with carbon holding the EGR valve open causing a rough or no idle. A number of fixes are available for this problem including:
• A service fix of a PROM to exercise the valve, increasing the opening periods at highway speeds is available for 1991-94 models, and a new flash programming for '95 vehicles.
• An aftermarket screened gasket to prevent this condition from recurring, TOMCO # 2-1357.
• A chemical cleaning kit, requiring chemical to remove and clean out the EGR passages. The utilization of this method has prevented many comebacks and should be looked into as a maintenance service.
MAF Dirty Wire
A problem part that has become increasingly common is the hot-wire style Mass Air Flow used in many vehicles today. This is often caused by improper air filter service, which eventually allows dirt or filter fibers to wrap around the MAF hot wire sensor elements.
There has been some discussion on Internet discussion forums as to the proper method of repairing the unit, with some votes for replacements and others for cleaning the unit using some caution. Our testing shows that the new unit usually has a much better response, though we have also cleaned quite a few with great results.
