© 2011 by Hib Halverson
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Even though, for the last 25 years, computers do the "thinking" for our Corvette engines, old-fashioned vacuum operates control devices, such as analog EGR valves, canister purge valves, MAP sensors, dashpots, delay valves and so forth. Vacuum actuators are more common on C3 and 4 than on C5 or 6, but vacuum still plays some role on all Vettes with computers. Diagnosing vacuum devices usually requires a temporary source of suction, typically a hand-operated pump which are available from several vendors. Actron, Kal-Equip and Lincoln Industrial are all tool manufacturers which market hand pumps.
I use a Lincoln Industrial Mityvac because of its ease of operation, rugged construction and a manual which not only covers the tool's operation but offers tips on troubleshooting with the device. Other reasons are: familiarity-I've used Mityvacs since my earliest days in the service trade-and durability. In more than two decades doing this stuff, I've owned three Mityvacs. The first was an original plastic unit which I bought ages ago and used for almost a decade until I broke it in a fit of anger at a car which was "failing to cooperate". To replace that, I acquired a Silverline, the all metal Mityvac-perhaps metal was a better choice considering the effects of my temper has on tools made of PVC. I used that unit for about a dozen years until early 2011, when I replaced it with one of the redesigned, Silverlines (PN MV8510 or, sold by Matco Tools, as PN MVP5000).
The old Mityvac design had been in production for several decades. In 2009, responding to growing numbers of turbocharged gas and diesel engines with computer-controlled waste gates or supercharaged engines (LS9 in the 3G ZR1) with computer-controlled bypass valves, the testing of which requires a consistent source of pressure, Lincoln Industrial updated the tool to improve its pressure performance. The new Mityvacs generate pressure in an easier and more consistent manner. In addition, Lincoln improved the look and ergonomics of the tool as well as adding new features such as: interchangeable front hose connectors and a gauge which, for easer viewing, is angled and can be rotated. I've worked with the new Silverline for about a month and conclude that this redesigned Mityvac is a significant upgrade. Indeed, the tool's performance in the pressure mode has been improved. The rotating gauge is a useful enhancement. Another great feature is the new design's better ergonomics-it fits your hand more comfortably making for less fatigue in a work session requiring a lot of pumping.
All Mityvacs produce vacuum and pressure and include ports for both. However, "dual vacuum/pressure converter" pumps, such as the Silverline, allow switching between vacuum and pressure at the front port and have a compound gauge indicating levels of both. The dual-converter feature is an added convenience which makes diagnosis of pressure devices easier.
Lincoln Industrial, also, markets a high-value line of Mityvac pumps, called "Selectline". They are made of PVC plastic and (unless you throw tools across the shop when you get mad at your car) are excellent choices for occasional-use, DIY engine controls diagnostics. All of the PVC Mityvacs received the same design improvements as the metal Silverline. The Selectline unit which duplicates the Silverline's functions is the 8255. If you're on a tight budget and you don't need the a dual converter pump's pressure function, the entry-level Selectline (PN 8010) is a good choice. Matco Tools sells the all-metal Silverline on its web site. The Selectline 8255 and 8010 are available from Amazon.com.
In Part One, we covered "flash-code" diagnostics on '81-'93s and '94-'95 ZR-1s, which are enabled by connecting the diagnostic link connector's (DLC) ECM diagnostic pin to its ground pin then turning on the ignition without starting the engine. The cheapest tools covered in this article are "code access keys." Marketed by Mac Tools, Wells Manufacturing, JC Whitney and others, these fork-like, steel stampings join pins-A and -B of a 12-pin DLC and are easier to use than a jumper wire.
Do the same task in a more foolproof manner with Zip Products' "Diagnostic Grounding Plugs". There are two sets of four plugs each, one for '82-'93s (PN TL-162) and the other for '94-'96 (PN TL-163). Each plug commands a different computer into its flash-code mode. '82-'89s only have ECMs, but '90s and up have as many as five systems which flash codes. We like the convenience of simply pushing a plug into the DLC, then turning on the key. Actron, also, markets a grounding plug (PN CP9001), but, since the two products are priced the same, Zip's is a better value because you get plugs for all codes one may need to read rather than one plug which supports only ECM and ABS.
"Code readers" are for OBD-II systems only and available from several vendors. They display diagnostic trouble codes (DTC) and can clear codes. A few display other information, however, none display ECM serial data. Popular are the Actron "PocketScan" (PN CP9125) and the AutoXRay "Code Scout 700", but we feel they're of limited value to serious DIYs because all they do is display and erase codes. To C5 DIYs, these products are worthless because their capability is built-in those cars. We, also, evaluated Actron's "PocketScan Plus" (PN CP9550) which is not a scanner but a code reader which, also, displays freeze frame data and OBD-II monitor status. That it reads those other two types of data makes it somewhat more useful, but again, we're not that fond of code readers.
All '81-'08s transmit diagnostic data over a "serial data link". To read that information, you need a device which "scans" this serial data and "scan testers" (also a "scan tools", "scanners" or "testers") do that. In our opinion, anything which cannot display serial data is not a "scan tester" and manufacturers characterizing code readers or grounding plugs as "scanners" are misleading their customers. While additional features in products like the CP9550 can be informative, because many DTC solutions require serial data; they and other faux scanners are of limited value at best for a Corvetter doing engine controls diagnosis and service.
While there are some diagnostic situations where a scan tester is unnecessary, a tester is an efficient way to interface with your Corvette's on-board diagnostics. For OBD-II systems, they're the best way-sometimes, the only way. Scan testers read and clear DTCs, and show engine parameters. Most record data-a feature valuable in solving random or intermittent problems. When connected to an OBD-II car, scanners display the system's failure records, or "freeze frame" data, limited histories of conditions present when a DTC sets. They display OBD-II monitors and "I/M readiness" data-whether or not your engine is ready for an exhaust emissions test. Some testers support GM "enhanced functions" which gives you about 50% more data. Some testers are "bi-directional"-they temporarily control engine functions for diagnostic testing or component initialization. Lastly, some have DMM and oscilloscope functions making them more valuable as diagnostic tools.
There are two types of scanners: hardware devices and scan test software for personal computers. This article covers hardware-based devices. We'll cover software-based testers in Part 3 of this series. We divide hardware-based testers into two segments: $250-1000 consumer units for basic/intermediate DIYs, which we cover here, and testers marketed to professionals and advanced DIYs selling for $1000 and up which we'll save for Part 3.
We evaluated several consumer-grade scanners from SPX Corporation's Actron and AutoXray divisions. We, also, tried out a couple of entry-level consumer-grade units, the Actron CP9575 and the CP9580; a mid-level unit, the Actron "Elite AutoScanner Pro" (PN CP9190) and a high-end consumer scanner, the AutoXray TechScan 7000. We, also, asked Equuis Products, Inc. to supply some of its "Innova" brand testers for evaluation but it failed to respond prior to our deadline.
For a control in this comparison we used our MTS-3100 Mastertech scan tester, a professional-level piece of equipment marketed to the service trade by Bosch Diagnostics. In this evaluation, if the testers were OBD-II only, we used '04, '08 and '09 Corvettes along with a '99 Blazer, '01 Camaro and '07 HHR. If the scanner had OBD support, we used '82, '89 and '95 Corvettes.
The Actron CP9575 is a basic scan tester in a compact package. Its diminutive size is why it's favorite of ours because it fits in the glove box or center console, ready for quick diagnostic evaluations. It's scan test functions are limited-it reads the global OBD-II serial data only, along with, codes, freeze-frame data and I/M monitors-but we've found the little Actron perfect as a "quick-and-dirty" scanner to keep in any project car. It even slips into my back pocket. Sometimes I carry it around at shows or on the trips my Corvette club takes. That way, I'm always ready when someone says, "You know, my check engine light is on. I wonder why?"
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Actron, also, makes our favorite itty-bity scan tester, the CP9575. I can't tell you how many times, I've popped this baby out of the glove box of a project car on a road test to look at some engine controls parameter or clear one of those pesky DTC coolant warm-up codes. It is so small, it fits in my pocket. I love this tool!.
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The CP9575's bigger brother, the 9580 is the the best value in an entry-level, OBD-II-only, scan tester on the market at this writing, May 2011.
The CP9580, a bit larger than the 9575, adds a host of additional features such the ability to record and playback serial data, customized data lists, graphing capability, ability to read and clear ABS codes on '96-up cars and battery power for offline playback of data. The 9580's unique "Code Connect" feature is a database of three million verified fixes for trouble codes. These actual vehicle fixes have been reported and then verified by Actron's ASE-certified technicians. If you only work on 1996 or later cars with OBD-II diagnostics, the Actron CP9580, at $299.99 MSRP and street-priced at 150 bucks at Amazon.com, is the best value on the market in a conveniently-sized, entry-level tester.
A "mid-level" scan tool, as well as reading global OB-II data, needs to support "GM Enhanced" OBD-II diagnostics along with pre-1996 systems, which some call "OBD-I" but are properly termed just "OBD". The mid-level unit we tested was the Actron Elite AutoScanner Pro, but just forget the long name and use it's model number, CP9190. This Actron supports engine controls diagnostics on Corvettes back to 1984. It, also, supports GM Enhanced OBD-II data up to 2006. In addition to all that, it will connect to Chrysler and Ford products' OBD back to the mid-'80s. The 9190 is actually a kit which includes cables needed to connect to all OBD-II systems along with GM, Ford and Chrysler OBD systems, a USB cable for updates, and the power cable needed when connecting to pre-'96 systems. The CP9190 lists for a little over 500 bucks but can be had for a lot less at Amazon and similar vendors. If you are going to only work on an OBD-II car, Actron sells the CP9185 which is just the scan tester and an OBD-II cable without the other accessories offered in the CP9190 kit.
All these Actrons support the computer area network (CAN) interface used on Vettes from 2006 and up. They all are "trilingual" (display in English, Spanish and French) and the CP9550 and the GP9190 have USB ports for software updates via the Internet and Actron's "Scanning Suite 3.0" software application which is a free download.
Moving up the price scale, the final step on our "$1000 or less" scanner list is the AutoXRay Techscan 7000. It supports Corvette back to 1982, global OBD-II data up to 2011 and GM enhanced data up to 2006. Of interest to those with cars other than Vettes will be the 7000's support for Ford, Chrysler and Toyota vehicles. A 7000 has a 128x128 pixel, 15-line screen. It doesn't require accessory power from '82-'95s because it has four AA batteries. It's easy to connect, simple to operate and worked well with every Vette ('82, '89, '95, '04 and an '08) to which we connected it. The Techscan kit comes with DLC connectors for GM, Ford and Chrysler along with a USB cable to link to a PC.
The AutoXray Techscan 7000, even with a higher price, is a solid value for Corvette DIYs and an excellent choice in consumer-grade testers. It lists for $650 but can be found for less at Amazon and others and, even with some accessories, such as the available ABS support and the optional "EX-PC AZ500 software" (allows you to store and graph captured data), at street prices, it is still going to come in under our limit of $1000.00. In the next part of "DIY's Dose of Digital" we'll survey professional-grade scan testers, scan test software for PCs and maybe have a more detailed discussion of '96-up OBD-II diagnostics.
Auto Meter Test Equipment
413 W. Elm St.
Sycamore IL 60178
2030 Alameda Padre Serra
Santa Barbara CA 93103-1716
Fluke Corp. (Fluke and Raytek)
Everett WA 98206
Hickok, Inc (Waekon)
10514 Dupont Ave.
Cleveland, OH 44108
Danaher Tool Group (KD Tools)
14600 York Rd.
Sparks MD 21152
Lincoln Industrial (Mityvac)
One Lincoln Way
St. Louis MO 63120
4403 Allen Road
Stow, Ohio 44224
Schumacher Electric Corp.
801 Business Center Dr.
Mount Prospect IL 60056
Simpson Electric Corp.
Lac du Flambeau WI 54538-0099
28635 Mound Rd.
Warren MI 48092-3499
8067 Fast Lane
Mechanicsville VA 23111