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Fixing Cars Via the InternetPosted 12/9/1999By Jim Linder
This month I want to share with you a few "fixes" that were initiated on the Internet. If you haven't signed on in a while, there's a lot of good information out there if you hit the right sites. If you're a member of the International Automotive Technicians' Network (iATN), it is a great online source to exchange technical knowledge and information with other members from around the globe. Fixes are posted daily on the network (http:// www.iatn.net) and it has become a must-do tool for the automotive service technician. The following is an interesting "Internet fix" for Ford vehicles.
Case 1 The test procedure is fairly straightforward: Use a test that was developed by Randy Bernklau first; next, hook up to the MAF signal wire and set up the scope for single shot, positive trigger, 500mv/div, 100ms/div, trigger level set at1.2v or so. Delay 2 to 3 divisions, or whatever puts it in the center of your scope.
Now you're ready for a brief WOT snap. Clean the dirty MAF and rerun the test. See Figure 2 (right). Now, replace said MAF and pull in the next car. Yeah, you don't have to replace them all, but on a personal note to "Pete" (I hope he's reading this), you might have shipped this one - VBSEG. The ping was gone after the cleaning, but I still didn't like how the power felt uneven under load. Here's the wave (Figure 3)
The PCV hose was leaking and was soon found by a smoke machine. The small bottle is stabilant 22, a real good idea with MAF connectors (or any connectors) where small voltage drops can cause problems. A while back I cleaned one and got away with it, but Randy says he usually replaces them. I now agree. Also, I like to see 3.2 volts at a minimum on a WOT snap. I have many waves now; even a 1.9 SEFI can hit 3.8 Vp. I have experimented with dead cylinders and messing with the timing without affecting the waves much; it's still pumping air. I hope this helps someone fix a lean Ford, or maybe even a lean or adaptive limit code setter. (My thanks to Randy Bernklau for this one.) Case 2 An iATN friend in another state sent us an e-mail about a customer's father who had a continuing problem with a late-model, high-mileage (142,528 miles) 1993 Plymouth Grand Voyager equipped with a 3.0L V-6 engine. The vehicle owner was disgruntled with the inability of a couple of shops to repair the 40- to 45-mph surge with replaced plugs, cap, rotor, wires, cleaned injectors, fuel pump, timing chain and fuel filter. He had asked his son (in another state) for help from his local service facility.
Note: I don't disagree that all this may or may not have been needed, based on mileage. The fact is, the original problem was - and still is - there! After answering the e-mail, the vehicle was brought in to us for analysis. During a test drive, we felt as if the problem was EGR-related. Unplugging the EGR fixed the problem, but magnified the spark knock situation observed on the test drive. Further testing showed (with a smoke test) a leaking EGR transducer (normal with no exhaust back pressure applied). See Figures 1 (above, left) and 2 (above, right).
When pressure was applied to the transducer, the valve still leaked badly and was removed from the engine. (See Figure 3 - left) Further examination (Figure 4 below) showed the internal leak and the exhaust heat damage caused by many moons of driving this vehicle. Exhaust back pressure pushes upward on diaphragm (torn in picture) and closes EGR solenoid vent port to allow EGR to open when commanded by PCM. This unit with the hole would allow the EGR to cycle open and close, causing jerk at 40 to 50 mph.
A new EGR transducer was ordered for the vehicle, installed and the vehicle is repaired. I believe this repair shows a new method of Internet utilization with online contacts all over the world.
Case 3 Some time ago one of the DATA center technicians came to class and asked the following question: How does the GM coolant level unit operate? It seems as if the switch is in a dry hole and doesn't actually contact the coolant so the question becomes: How does it know? Thanks to Curt Marsh, from Marsh Garage in Indianapolis, we now have one apart and can discuss the circuits and the operation of the "Low Coolant Level Indicator" found on a number of late GM vehicles. The coolant level switch is an assembly containing a reed switch and magnetic float. When the coolant level is normal, the float rests away from the reed switch, causing the switch to open. When the coolant level is low, the float rests near the reed switch and the switch closes.
The coolant level switch (Figure 1) is mounted in the radiator surge tank (Figure 2, right). If the coolant level falls below a specified level, the switch closes, sending a ground signal to the powertrain control module (PCM). The PCM will then send a signal to the instrument panel cluster (IPC). The IPC will then illuminate the low coolant level telltale lamp.
Service tips:
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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A Ford Ranger (left) sent from another shop had been diagnosed with a pinging complaint caused by carbon. They had also removed the octane shorting bar, which retards the timing 3 to 4 degrees. On an engine that does not use an EGR, removing the octane shorting bar means something's amiss!
And here's the fix (left).
Our second Internet fix is somewhat different but also shows the value of an Internet group.
Did you ever wonder how a circuit or a particular device worked? I feel this is the trait that separates fair service technicians from very good ones.
