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Re: REALLY stumped on this no start even after Ari's list.
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Fri, 21 Jul 2006 05:11:05 Share Post by Email
In Reply to: REALLY stumped on this no start even after Ari's list., ProfKenn, Thu, 20 Jul 2006 16:14:58
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A few thoughts-

The first is to forget cause-and-effect. We all like to think that the engine isn't running because we fiddled with something, so all we need to do is un-fiddle it. After years working in diagnostics I have learned that weird stuff happens. Sometimes something fails because it decided to fail, and the fact that you fixed something on the other side of the engine is just coincidence. Think of it as an episode of CSI - follow the evidence, and don't assume. If it turns out the problem is due to something you did (or didn't do right), a methodical process will get you back there.

So ignore what you know and start from scratch. To run requires air, fuel, fire.
First question - does it sound 'right' when it cranks? Is the engine note different? Pull the fat hose off the AMM and hold your hand a few inches in front of the AMM intake as someone cranks the engine with the throttle open. You should feel the intake of air in pulses, and shouldn't feel air getting pushed out. You could do this at the intake, but I'd prefer the AMM, as it has a screen that will prevent big items from being sucked in. What is this doing? It is making sure air is being pulled in. Why wouldn't it? Maybe that rag got dislodged after driving and is stuck in the intake. Maybe the timing chain broke and the valves aren't opening (sorry, had to say it). Maybe it slipped a few teeth and the valve timing is way off. The engine would sound wrong as it cranks.

Next, REALLY check the DI. Buzz and hum aren't enough, because the engine isn't running. Pull it out, flip it over. Stick plugs into each boot, and ground each plug. All plugs must be in place, and ALL plugs must be properly grounded. Crank the engine. Do they all fire?

When the engine starts, the DI fires in a hail of sparks. If it is working and there is gas (and air), the engine will at least cough and spit. You didn't mention C&S, so I immediately think ignition.

The plugs are wet. That could be from residual fuel pressure in the lines. You've verified the fuel pump runs - good. But is the fuel pump relay pulling in? You can measure the voltage at the fuel pump relay as the engine cranks - it should be 10 volts or so (battery cranking voltage). If you don't see a good voltage there (5 volts or less is too low), suspect either the fuel pump relay, or that the ECU isn't telling the relay to run. Ideally, you'd like to know that you have both good fuel pressure and fuel flow, but at least be sure the FP runs when the engine is cranking (when it counts).


Of course, inspect each plug. Use a flashlight to look into each piston. And I like yaofeng's idea - go back and re-seat the connectors on all of the major player boxes - ECU, etc. Yes, I know you didn't touch the ECU - humor me. If you've determined that you have good spark, plenty of fuel, and good airflow, then the only thing left is that your engine is possesed by a demon and an exorcism is in order.



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