An Emissions Repair "Dirty Dozen"
by Brian K. Manley The top of the agenda sheet read: "Colorado Emission Technicians Night. Purpose: To share repair and diagnostic experiences and successes; no hypin’ or gripin’ about ‘the program’ — just what finds and fixes emissions failures and why."
I was stunned, having attended seminars and classes touted as "advanced" or "for professional technicians," only to sit through hours of basic information and come away with little ammunition to take into battle on the next business day. No, this gathering was going to be different, and over the next two hours I gathered repair strategies that would help me in the fight to fix emission failures.
Held in a Nissan dealership’s service facility, we heard repair techniques from Colorado Department of Health technicians, technicians with Diagnostic Technician Education Consultants (DTEC), and many of the top independent and dealership emissions and driveability technicians in the Denver metro area. I’d be remiss if I didn’t share the contents of this meeting with other emission repair technicians. The following "dirty dozen" problem cases were presented by state officials and elaborated upon by the rest of the group. Many of these repair strategies are designed primarily for vehicles in high-altitude areas, but the gross CO and HC failures that are repaired here can appear in any basic or enhanced area.
One warning: Re-jetting should only be performed after all other systems on the vehicle have been evaluated and are in proper working order. This includes, but is not limited to: basic mechanical condition of the engine, basic engine adjustments, evaporative emission systems, catalyst integrity, computer control systems and vacuum routing.
1) Ford 1.6L Escort. This Escort has an initial I/M 240 failure rate for CO exceeding 50 percent. It has been labeled a "pattern case failure" and studied extensively to verify the effectiveness of accepted repair strategies. At Seyfer Automotive we have developed a strategy to re-jet this Motorcraft model 5740 carburetor. Two Escorts that were used in the state’s Repair Verification Study are profiled here. One Escort had CO emissions exceeding 200 grams per mile (gpm) on the I/M 240 test and the second had CO values of 55 gpm. To drop CO emissions under the cut point of 30 gpm required recalibration of the main metering circuit. A wide range of various-sized main jets, primary air bleeds and secondary air bleeds can be purchased in the aftermarket for these carbs (see photo on page 16, item No. 1). After recalibration of the main circuits, both vehicles received a "fast pass" upon reinspection at the I/M 240 test facility. A "fast pass" indicates that emissions were low enough to stop the test early. Fuel economy increased in the first Escort by 8 miles to the gallon, and the second by 1.1 miles to the gallon.
2) 1991 Chevrolet Caprice, 305 CID engine with TBI. In Colorado, this vehicle has an initial I/M 240 failure rate of 32 percent. Failing multiple retests, the average reading for this car is 40 gpm, ranging from 16 gpm to 62 gpm. To isolate the root cause of this pattern case failure, Chris Chesney of DTEC and state technicians systematically evaluated all PCM inputs and outputs on one of the failed vehicles using a lab scope, a scan tool and a dynamometer. All serial data appeared normal at idle and at cruise, and no check engine light came on. Many sensors and components had been replaced on this car with no measurable improvement in emissions. With the vehicle loaded on the dyno, the fuel injector waveform (see page 18) showed an intermittent asynchronous mode when compared to the distributor reference signal (DREF). After condemning and replacing the fuel injectors, the Caprice passed multiple retests and came close to the Federal Test Procedure (FTP) CO emissions requirements.
3) General Motors 2.8L, non-feedback Varajet. These vehicles can fail basic and enhanced tests, and I usually see I/M 240 CO readings at 100 gpm! Ever see one of these carbs pull fuel from the main venturi while idling? Jay Kidwell from The Carburetor Shop had several suggestions about addressing this "bleeding over" condition:
• Advance the base ignition timing, reduce the vacuum advance.
• Reduce unmetered air by rebushing the throttle shaft bores and replacing the throttle plates.
• Re-adjust the throttle angle so the idle transfer port is not exposed.
• Watch for "loaded" vapor canisters and verify the integrity of the AIR system.
Last week I worked on one of these carbs on a Canadian vehicle. This 1985 Olds Cutlass failed an enhanced emissions test at 105 gpm CO on a 30 gpm limit. This vehicle also had border papers that exempted it from Environmental Protection Agency (EPA) regulations, so it did not have air injection or a feedback carb! I road tested the vehicle, baselined the in-stall exhaust readings, followed approved diagnostic procedures and recorded my findings. I recommended the aforementioned carburetor and timing adjustments, and a re-jetting procedure.
To make a long story short, after searching in vain for smaller jets from our suppliers, I reduced the size of the main metering jet (photo on page 16, No. 3) by .007 -- by filling with solder and re-drilling with a jet drill and a pin vice. I also trimmed several coils off of the spring under the power piston assembly to reduce power circuit enrichment. The car returned to the lanes and passed with a 29.5 gpm CO reading on a 30 gpm scale! Whew! NOx did increase on the retest, but stayed well below acceptable limits. Note: I’ve replaced the "180" jet found in low-altitude certified carbs with a "174" jet that I found in a high-altitude carb. The part number for this "174" jet and rod package is #17110238. (If you can find one. Some parts people say it’s discontinued.)
4) Hyundai/Mitsubishi feedback (Mikuni) carbs. Many emissions failures, under loaded and unloaded conditions, are caused by high CO readings related to these carburetors. The air bleeds can be replaced or drilled to reduce CO, and this can be done with the carb on the vehicle. Other items to look for are:
• Failed mixture control solenoids. I’m told that these can be purchased separately from the air horn, but require slight modification to the casting.
• A properly functioning coolant sensor. The system won’t go into closed loop without it.
• The catalytic converters on many of these cars are plugged from running rich. These are the ones that bolt directly to the exhaust manifold. One tech said that there is an aftermarket source for these, so don’t give up!
• Verify the condition of the high-altitude compensator (HAC) before drilling the air bleeds on these carbs.
5) 1985 Honda Accord. Many of these failures that we’ve seen have a VECI decal that reads, "Low altitude only does not comply at high altitude." There were many suggestions for these failures including:
• Watch for plugged filters in the HAC on driver’s side strut tower.
• These Accords have power-controlled frequency valves. If using a lab scope, "on" is high voltage. These can go to 100 percent duty cycle.
• These systems need to see a speed sensor signal to go into closed loop. The sensor is in the speedo head, so guess what a broken speedo cable will do!
• Check for air temperature sensors that were left unplugged, or plugged into an incorrect lead, after the air cleaner housing was reinstalled.
• My friend, Scott Hopkins-Stutz, who has worked on several carbs on these Accords, says, "You can’t buy jets for these, and they can’t be removed."
• You can enlarge the .018" air bleed jet that is in the primary venturi to .035". Also enlarge the .032" air bleed passage to .035". I understand that this recalibration of the air bleeds can produce the same results as a $1,000 air horn and high-altitude package from the dealer.
6) Mid ’80s Oldsmobile 5.0L VIN "Y" with feedback E4ME 4bbl Quadrajet. We’ve seen these cars run as high as 250 gpm CO! Our group compiled a list of tips including:
• The canister purge valve has high failure rate if it’s on the intake manifold.
• Beware of an inoperative thermal vacuum valve (TVV) or incorrect vacuum hose routing.
• If these carbs are the 2-point adjust style, be certain to adjust the lean and rich stops correctly!
• Check dwell readings under load, not just in the stall.
• TPS adjustment is critical and can cause gross failures. If out of adjustment, the computer receives a "wide open throttle" signal too soon, causing full enrichment and fixed timing.
• The AIR system may have management valve failure. If air is diverted upstream with a hot engine, the oxygen sensor will interpret this "false air" as true exhaust oxygen content and send a rich command to the mixture control solenoid!
7) Early Chrysler feedback carburetors with Electronic Fuel Control (Lean Burn) Systems found on 2.2L and 5.2L engines. Note the following:
• Power valves fail consistently.
• A closed signal from the throttle switch will result in fixed timing and fuel, so if this switch is shorted, driveability and emissions problems will result.
• Several technicians agreed that spark control computers can be defective right out of the box.
• Temperature switches are just switches, not NTC thermistors. The coolant and charge temperature switches affect EGR enable, air switching from upstream to downstream, canister purge and fuel feedback status.
• A 2.2L engine control system requires a speed sensor signal for closed loop. I’ve seen a fuel-injected 4-cylinder Chrysler system that needed to see "D" from the PRNDL before going into closed loop. Read the enabling criteria for each system before condemning any parts! The photo below left shows a 1984 Dodge truck with a 318 CID engine. After a carb rebuild and a new air pump, this truck got a fast pass on the I/M 240 test!
8) Ford 200 CID, 6-cylinder engine with a non-feedback Holley model 1946 carburetor. My test for these carbs is to "grab and twist." If the main body moves or lifts completely off of the throttle body (I saw one like this once ... and it was idling!), then you know that you’ll at least have to R&R the carb to replace the loose or missing throttle body screws. Besides loose carb parts, other items to watch for are:
• Burned-through EGR plates that mount under the carb. Can you say "hydrocarbons?"
• Be sure the air injection systems are working correctly and that the air pump is producing enough volume. (O2 readings on your emissions analyzer should rise at least 2 percent to 3 percent when enabled.)
• Perform a catalytic converter test. The oxygen absorption test is the first one that I learned, but the GM method seems to be preferred by most techs.
• Power valve opens at 12" hg. This can be delayed by removing the brass plug from the top of the power valve assembly, gently heating the Allen screw to loosen the threadlocker (with the power valve assembly removed from the carb), and turning the Allen screw to reduce the spring tension. In some cases, the spring will have to be trimmed to reduce cruise CO enough to clean up emissions.
9) Toyotas (and late-model Chevy Novas) with the electronic air bleed control valve (EBCV) mixture control system. As the name suggests, this system uses a richer than normal main metering circuit and bleeds air into the main circuit to control the air-fuel ratio. Several of the following tips were presented by a Toyota master technician:
• Watch for rubbed-through plastic vacuum lines.
• This system needs to see a throttle switch input before going into fuel control.
• Beware of pellet gun BBs in the HAC hoses. That’s right. Some tech working on the vehicle may have left a BB, used as a self-styled "anti-hesitation" valve, in a HAC hose.
• Watch for a "V" cut in the lowest hose of the HAC (some technicians’ way of compensating for a plugged HAC filter).
• If your vehicle has an "A" and a "B" vacuum switch, watch for swapped vacuum hoses.
I have seen a bad distributor vacuum advance diaphragm cause low system vacuum and a rough-running engine on this system. I’ve also seen bad auxiliary accelerator pump (AAP) diaphragms that will cause extremely rich running engines. This diaphragm is used for cold enrichment, so if it is ruptured you’ll see a rich condition until the engine warms, unless the TVS that controls the AAP is stuck open, then you’ll have a constantly rich-running carb!
10) Feedback Hitachi carbs found on the Nissan Sentra, Subaru Justy, Isuzu Pickup, Mazda 323 and GLC. Hopkins-Stutz has worked on many of these cars and has compiled this list of common "opportunities" to look out for:
• Failed duty solenoid. You can purchase just the duty solenoid separate from the air horn. Have you ever called Nissan only to hear that you have to buy the entire air horn for $400 or more, just to get the solenoid? The part numbers are: duty solenoid, part # 16197-61A03 and air horn gasket part # 16455-33M22. (Some parts sources may say this part is for California cars only, but the solenoid will fit 1987 Nissan Sentras built after January 1986.)
• Hopkins-Stutz has seen up to negative 2 volts on the O2 sensor wire because a non-factory replacement battery cable did not have a pigtail ground strap! This voltage drop across the O2 sensor sends CO through the roof.
• The large PCV hose on these engines will soften from exposure to oil and collapse. Without this calibrated air entering the engine, the vehicles often run too rich.
11) Jeep Wagoneer, 360 CID, 2 bbl Motorcraft non-feedback carb. These engines often fail enhanced emission tests at 200 gpm CO, and fail basic tailpipe tests for high CO at 6 percent to 10 percent.
• Power valves love to blow on these carbs. If your carb has its power valve hose running from the base of the carb to the intake, simply remove the hose and check for fuel. Several at the tech session said to switch from a "54" main jet to a "52" main jet. The part numbers are: C3GY-9533C for the 54 main jet: and C3UZ-9533A for the 52 main jet.
• If these engines have been running rich for too long, the catalytic converters may be coated beyond saving.
• Watch air pumps for proper output and the air injection system for proper functioning. I’ve seen a lot of rusted or removed air injection manifolds and burned check valves on these trucks.
• Check the EGR system for correct vacuum hose routing and any stray "anti-hesitation" BB pellets.
12) Ford 3.8L central fuel injection (CFI). A plethora of possibilities exist on these systems for driveability and emission problems, including:
• The O2 sensors must pass the response and calibration tests. If there are two sensors, they must switch together! I’ve seen one sensor disconnected and the other senior sluggish on the same vehicle.
• Check for TSBs or recalls involving the AIR system.
• Engine coolant temperature (ECT) and air charge temperature (ACT) sensors must be checked for sensor "drift" and reliability. The ACT often becomes coated with oily blow-by and will give erroneous values to the PCM. Both sensors should be equal with a cold engine and should be monitored during a warm-up cycle.
• EGR valve position (EVP) sensor. I have seen a grossly out-of-range EVP shoot CO readings off the scale.
• Throttle position sensor (TPS). A lab scope is the only way to test these sensors. Last week I had a customer complain of stalling, surging at cruise and rough idle. The TPS was breaking up at idle. If the signal from this sensor is out of range, high emissions can result. Guess what happens when one of these is stuck at 4.5V at idle? The car won’t run because the PCM sees "clear flood" mode, shutting off trigger to the injectors.
Sharing Information
In a world full of complex vehicle systems, information is the single most important weapon that we have when faced with difficult emission or driveability situations. This "Colorado Emission Technicians Night" was two hours well-spent. I learned new repair strategies and reinforced old ones. I hope this practice of information sharing continues between dealers, independents, state officials and training companies for a long time to come.Brian K. Manley is an automotive instructor at Smoky Hill High School in Cherry Creek, Colo., and also instructs for DTEC, a technician education firm based in Aurora, Colo. Manley is a National Institute for Automotive Service Excellence (ASE) master technician with L-1 certification. A longtime technician, Manley works full time during the summer as a technician and consultant at Seyfer Automotive in Wheat Ridge, Colo.
ASA Main Page || AutoInc. Main Page
TechTips || Stat Corner || News Briefs || Directions
News Briefs Extra || Taking The Hill || More Info About AutoInc.
Chairman's Message || Tech To Tech
Guest Editorial || Diversifying Your Collision Shop || National VOC Rule Sparks Congressional Interest
AutoInc. Magazine ®, Vol. XLIV No. 8, August 1996