NO POWER
Dear Roy,
I have a 1990 Cadillac Deville sedan with a 4.51 throttle body injected engine and automatic transmission, VIN # 1 G6CD53 7L4342078.
The owner brought the car in because it was running poorly. We found three bad injectors and one weak one. We replaced the bad injectors and the car would idle fine, but only had 7 in. of vacuum.
The first thing that came to mind was a plugged catalytic converter. We checked this and found it good. So I pulled the timing cover and checked the chain because I could not get the timing mark to line up properly. While doing this, I found that the harmonic balancer had slipped, but the chain marks were fine. I replaced the balancer and put the unit back together.
We had a class from [a manufacturer] on its injector cleaning machine, and they said that it could be from a plugged-up intake manifold. We cleaned the manifold, injectors and EGR system. I still have the same problem: only 7 in. manifold vacuum and no power at all. Leak down tests show only 15 to 20 percent leak down and the compression is from 130 to 155.
We also have replaced the ECM. Do you have any suggestions for me?
Thanks for your help.
Jerry Wessels
J&W Automotive Service Inc., Laramie, WY
Dear Mr. Wessels,
From your letter, I can assume the engine has good sealing of all cylinders based on the compression and leak-down tests. The question I have is, has the vehicle been tested on an oscilloscope? Are all cylinders affected?
If they were, I would look for something that is likely to affect all cylinders such as a lean condition, valve timing, plugged converter, etc. However, if only certain cylinders are affected, I would perform a volumetric efficiency test by the use of a running compression test. Remove one spark plug at a time. Install your compression gauge with the Schrader valve removed. Start the engine and observe the readings. These readings will be lower than the results
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obtained during a cranking compression test. This is the result of higher piston speeds.
All cylinders should be within 20 percent of each other. An abnormally low reading indicates intake restriction or worn intake cam lobes while an abnormally high reading would indicate exhaust restriction or worn exhaust cam lobes. Hope this gets you on the right track.
The Missing Van
Dear Roy,
I have a 1997 Ford, E-150 Van, VIN# 1FTEE1422VHB07388, with a 4.2 L, V6, automatic.
Symptoms: It runs like you pulled off one of the spark plug wires, whether at idle or while driving. All six plugs are fouled after 50 miles, and it only gets about 5 mpg. Top speed uphill is only 35 mph. I have replaced the computer, plugs, plug wires and both oxygen sensors mounted in the exhaust manifold.
Tested: Coil pack, both primary and secondary; it ohmed out within specks. Compression is less than 5 psi difference between highest and lowest. Fuel pressure is correct with the vacuum line on or off. I have ruled out a plugged catalytic converter because there is one in each side of the
