Best way to disable engine starting

[Vikas]

I just had the battery replaced but I am "feeling" that the starting is becoming "weak". The car starts "instantly" i.e. within 0.2 second or less. The engine barely completes a single revolution before it catches. I put a DVOM on the battery and it is not able to catch the cranking voltage as the crank time is way too low.

My car has a separate fuse for fuel pump and another one for fuel injection. Here is my dilemma:

If I take out the fuel injection, ECU would most likely throw check engine light. If I take out the fuel pump fuse, car will stall but there would now be air between the fuel pump and the fuel injectors. Would I have issues once I put the fuse back and could I run in to air lock?

May be I over thinking this too much? All I want to do is to crank the engine for 5 second and measure the cranking voltage so I would know if the new battery is good or not. I think I want to see it staying over 10 volts given that it was replaced only couple of weeks ago.

I have already checked the alternator for proper output both under idle and load conditions and it is working fine at this time.

- Vikas

 

[Dave Sherman]

I'd be very surprised if it can throw a check engine light while cranking, normally the engine has to be running before that happens. I always pulled the fuel pump fuse and cranked the engine to relieve the fuel pressure on my Saturn when I changed the fuel filter. It always started right up after changing it, probably because the pump quickly purges the air through the return line to the tank.

DON'T pull the spark plug wires off though, ignition systems don't take kindly to that.

If you're concerned about testing the battery, take it to Autozone or one of those places. They'll put the load tester on and check it for free.

 

[Vikas]

I did not like disabling ignition idea because that dumps raw gasoline in the cylinder.

I thought Autozone/Advanced type of places wants the battery to be taken out before they will load test it.

- Vikas

 

[440Magnum]

Pulling the auto-shutdown relay should disable both fuel injection and ignition but allow cranking.

Pulling the fuel pump relay isn't likely to hurt anything either. The engine will start and run until the fuel pressure drops to a few PSI, but it wont "suck air" into the system so it'll fire right back up when you put the relay back in.

 

[eljefino]

Disabling fuel pump will be fine. You usually also get "clear flood" mode by flooring the gas; this reduces or eliminates the fuel injectors pulsing.

 

[Dave Sherman]

Originally Posted By: Vikas


I thought Autozone/Advanced type of places wants the battery to be taken out before they will load test it.

- Vikas


I hadn't heard that, Autozone load tested my battery while it was in the car.

 

[Vikas]

Guess what, it was actually the starter which was going bad. I had my mechanic put a Bosch reman. All of the intake air ducts needed to come off to get the access to the starter. Lots and lots of bolts and connectors came off. Fortunately at the end no "extra" bolts were found

Given that throttle body was exposed, we decided to clean the carbon which was accumulated over 154K miles. In retrospect, I should have not asked him to clean it. The computer has to adjust to newer and cleaner throttle body and I am finding some of the parameters on the OBD-II live data somewhat puzzling especially at idle. I have reset it couple of times but I might need a big battery disconnect overnight because I know on this car, only I/M and DTC gets reset and NOT the running parameter when OBD-II reset is done.

The mechanic is good but I think he is "too good" for my own comfort. He did all this work "live" even after I nudged him to disconnect the battery negative. I know lot of professional electricians change switches and sockets live but it always bothers me.

The instantaneous gas mileage at idle has gone up and the idle timing advance has gone down even after the idle speed as returned to the original. But the timing advanced while running seems to have gone up. STFT and LTFT parameters have not moved since cleaning of the throttle body.

The amount of carbon was not bad considering it was not touched in 11 years and 154K miles.

- Vikas

 

[Hardy]

You can disable any gasoline engine by turning off either the fuel, or the ignition. It is always best to disable the fuel. This will protect spark plugs from getting fouled, cylinder walls from getting washed down with fuel, and damage to the catalytic converter by overloading it with hydrocarbons.
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