Weird intermittent starting problem...

[yoshisushi]

Hi all,

OK, I did the tune up, new cap rotor wires and plugs, still happening. It's not a security Passlock problem because the symptoms don't match.

I had to drive around in a snow storm recently for about an hour and the truck died while I was driving (first time that's ever happened). I pulled over and made a call for a ride, 15 minutes later the truck started and I drove home fine. It kind of ran rough for the first 15 seconds but then ran fine.

My question right now is when I turn the key to ON and the fuel pump comes on, how loud should it be? Mine is LOUD! It's not bad sounding, not like a rock in a lawnmower sound but just loud like a vacuum cleaner is loud. Is that bad? People at work even notice it. I just thought that's how it's supposed to be.

Also, does it sound like a loss Spark problem or a loss of fuel pressure? I’m going to buy a fuel pressure gauge this weekend and when it will not start again I’m going to check the fuel pressure.

Thanks greatly for your help!!!

Rick

[Chevy-SS]

My fuel pump is also very loud. My friends have commented on it. I can sometimes hear it while driving and it is a little annoying.

Have you put a code reader on this thing? That may help. Also, you said you were going to try the resistor bypass trick? Did you do that?

[J-Ri]

It's not nescesarily bad because it loud. If you have access to an oscilliscope, look at the waveform of the fuel pump. It should be very even. The waves are where the brushes in the pump contact 1 or 2 contacts on the rotor. If the pattern is eratic, your fuel pump is bad.

[yoshisushi]

It finally happened again and I was able to get the code pulled at AutoZone.

It's Troublecode ODBII (Alpha) P Code. P1351 IDM Input Circuit Malfunction.

About all I can find on the web is that IDM stands for Ignition Diagnostic Monitor Input Circuit.

[marc_28269]

Originally Posted by Chevy-SS

I suppose I could be wrong here, but I though all GM vehicles used VATS or PASSLOCK. Introduced in 1996, GM has changed the VATS anti theft system to Pass-Lock system. This is a similar device to the VATS system, in that there is a resistor present during the start cycle. However, in the PASSLOCK system, the resistor has been placed inside the ignition switch, instead of the key. This is why you no longer see the resistor actually in the key itself. This is still a theft-deterrent device.

To remotely start a car with this feature, you must bypass the PASSLOCK system. There are two methods of doing so.. The first, is to permanently bypass this system. This is the easiest method for accomplishing your task and this is what I did. The second way, is to temporarily bypass the PASSLOCK, by introducing relays into the system, which retain all of the features of the system, while allowing your remotes start module to bypass it automatically during a remote start cycle.

Bottom line: your '98 truck uses PASSLOCK with the built-in resistor circuit, therefore you could certainly be having the problem that I was. After you get stuck a few more times, if you can't fix it, then do as I did and measure the cranking resistance, buy or make your own resistor of matching ohms and solder in place.

http://www.e-z.net/~iei/vatts.htm

There's a page with instructions. Go to the bottom and use Diagram A. Hope this helps.

Good luck

Is there a diagram available without the automatic start involved?

[Chevy-SS]

marc,

Just go to that page. At the bottom simply use Method A or B. I used (and recommend) Method A, which is a permanent bypass of the security code wire. You should be able to do the whole job in about an hour. You need something to measure resistance (an ohm meter), then you just need to go to Radio Shack and buy resistors to match (+/- 4%) the reading that you take. Solder the resistor in place as per instructions and you will have no more starting problems.

Of course, this bypasses an important security feature, but I'd rather be able to start my car, LOL.