Damnit! WTF!

[jamiholzbach]

I've been trying to address a low/rough idle, and while looking around for vacuum leaks decided it would be a good idea to change out the coolant temp sensor(it was covered in green corrosion on the outside & brown deposits on the sensor). After doing so, my idle got a little rougher, then I started to bog down(hesitate on initial acceleration) I started to hear a knocking. So, I parked it up for the night. the next morning I started it up, and it sounded the same. As I backed out into the street it stalled and will not start again. It turns over fine, I believe fuel is good as I have a pressure gauge mounted and it jumps up to 45 psi. I haven't checked for spark yet(ran out of daylight) but after reading some of the posts here I decided to check the resitance on the crank position sensor. It read at 533 ohms which I believe is within range (is it possible it went bad while still giving good resistance readings?) Also, it turns out I've got a 525 ECU instead of a 173 or a 153. Is this the wrong ECU? Help! Its gone from rough idle to no start over a CTS?

[jlevie]

The rough idle and hesitation on acceleration sound most like intake leaks. If they get bad enough, the engine won't start.

The fuel pump is controlled by the DME and only runs when timing data from a rotating engine (from the CPS) is presented to the DME. So if the pump is running when cranking the CPS is probably okay. But do check for spark.

A 525 DME is simply a later version and it will work as well as a 173 does.

[jamiholzbach]

Thank you Sir!

I've looked around, and other than some small cracks(not all the way through) on the intake boot I can't find anything. The hose from the throttle body to the valve cover is good, did not detect anything leaking where the fittings press into the throttle body, the vacuum hose to the FPR is good, and the gaskets for the crankcase tube are new. I'll check the valve cover gasket today when I do my spark check.

[jlevie]

Idle or hard starting problems are most commonly caused by intake leaks and/or
a sticky or defective Idle Control Valve (ICV). The only reliable method of
locating intake leaks is to have a smoke test run on the intake and crank case
and to test the brake booster with a gage and vacuum pump. The complete list
of possible causes of an intake leak is:

Intake boot
Throttle body gasket
ICV hoses & connections
Brake booster, hoses, and connections
Crank case breather hose
Evaporative control hoses, valve, and expansion tank
Fuel pressure regulator & hose
Injector seals
Valve cover gaskets & bungs
Oil filler cap
Dip stick o-rings
Oil return tube o-rings

While leaks in some of those can be found by inspection or by spraying carb
cleaner on suspect areas, not finding leaks that way doesn't eliminate the
possibility. Only a smoke test will really work.

[jamiholzbach]

Update...

Did a spark test yesterday evening, no spark! However, I had no helper to turn the key, so I jumpered between pin 11 & 14 on the diagnostic plug to turn her over( would that cause no spark?) the resistance values on the coil were not exactly what was listed in the Bentley manual, I got 1.1 ohms between 1 & 15, and 6330 ohms between 4 & 15 (is this still good?). So, I'm starting to suspect the 525 ECU? Oh, and by the way, I found a bad spot on the lower front corner of my valve cover gasket(vacuum leak?). What do you think Mr. Levie, am I correct?

[jlevie]

If the ignition was on when you jumpered the pins in the diag connector, there should have been spark.

Is power present at fuse 11 when cranking. That is the fuel pump fuse and will only be powered up if the DME is running and sees timing data from a rotating engine.

No timing data to the DME, a bad main relay, or bad fusible link are more likely than a bad DME.

[jamiholzbach]

Got it, will try again.

I 'll try the spark test again, this time with the key in the on position. I guess that the coil is good? I'm almost ready to just tear it apart and start all over again.

[jamiholzbach]

WTF Again!

I went to do a spark test again, and noticed that the fuel pressure gauge was down, now no fuel. So, early the next morning I decided to start from scratch, and try to troubleshoot the fuel problem( by the way I had disconnected my ECU the night before, thinking of swapping with my other ECU which happens to be a 380) I hook every thing back up, go to check for voltage to fuse 11, and when I turn the key, the damn thing starts!!? It runs but sounds like crap. So, I turn it off, and now it wont start again, but fuel pressure is back up.??? I'm now right back where I started. Ground? I've even swapped ECU's, the main relay, and the fuel pump relay and still no start. I'll try swapping the crank position sensor next, but I'm running out of Idea's. So far all sensors, etc. have checked good per the Bentley manual, but I'm still not getting any spark!

[jamiholzbach]

Oh Yeah!

and the fusible link checks good too!

[jlevie]

Put a test light on the fuel pump power lead. The pump is controlled by the DME and only enabled when the DME is running and seeing timing data from a rotating engine. So if the pump isn't running when you have no spark the possible causes are:

No timing data to the DME
No power to the DME or a bad ground
A bad DME.

If the pump is running when you have no spark the possibilities then become:

No power to the coil (which is provided by the ignition switch via C101)
A problem with wiring between the DME and coil ground
A bad coil
A bad ignition output section in the DME

Check for spark at the coil output lead, not at a plug. That eliminates the distributor, rotor, ignition wires and plugs from the picture.