'96 Jimmy hard start

[Realitydept]

HELP!!!

I have a '96 Jimmy 4wd, its been getting harder to start when cold. Once it starts, it runs fine. I changed the original plugs (125k), and they were shot, but it didn't change anything.

I'm still on the original cap, rotor, etc, but I don't think that is the issue. The ignition module near the coil is very hot after lots of cranking....

There is pressure in the fuel rail, as indicated by pushing on the valve and getting a good stream of gas.

I poured raw gas in the throttle body and that didn't help, so I think it is an ignition/ spark issue, any ideas?

R

[Realitydept]

I froze myself to death yesterday in the wind and cold to try and get it running, here's what I found.

Fuel pressure-steady 40psi. Relays work, pump runs, no pressure drop. This was with the car connected to a running vehicle with jumper cables.

I cranked the dang thing for an hour with no joy. I then went and got some starting fluid, sprayed it in the intake, and it fired right up. Once it started it ran fine.

I got it home, and again, it wouldn't fire without the starting fluid.

I changed the plugs a couple of weeks ago, and it never failed to start before I did. The yahoo at the parts store told me to gap them at .045, the book and underhood sticker say .060. Surely that wouldn't be the cause of this problem would it?

-Confused

[Realitydept]

I messed with it some this afternoon. I hooked the fuel pressure gauge to it, key on, 40psi. I then sprayed starting fluid in it, fired it up, and have between 50-55 psi when running.

As long as the fuel rail has that amount of pressure in it, it fires back up every time.

When the fuel pressure only builds to 40psi on key on, it doesn't drain back down to zero, so I don't think I have a leaking injector.

-more confused.

[94 Jimmy]

40 PSI ain’t enough.
If it's cold where you are, gas will not vaporize well. The injectors do a pretty good job of spraying a fuel mist into the cylinder, if they have enough pressure to work with. If they don't have enough pressure the gas just dribbles out of the injectors in droplets which are to large to evaporate in a cold engine. 60 PSI is what I've read is the minimum for my 94 Jimmy although pressures down to the low 50's will work, but with reduced flow, longer injection cycles and harder starting.
Since you've tried the starting fluid it's not a lack of spark. Regap you plugs to factory spec, go back to the parts store, get and change the cap and rotor. Winter puts a load on them and you might be shunting a lot of spark to ground or cross firing to another cylinder especially if you have any moisture in the cap. Also change the ignition wires, they have a synthetic fiber center impregnated with carbon powder to transfer the high voltage to the plugs, the center "conductor" often melts and becomes very resistive to current flow. I've been told that around 5000-10000 ohms/foot (for us techies) is the resistance for ignition wires. If you want to check that's fine, but at 125K I'd just replace them. I replace mine every 50-70K, it puts a lot less stress on the other ignition components, especially that ignition module which, as you know will fail at the most inopportune
time.
Good Luck, let us know what happens.
94

[Realitydept]

I've been screwing with it trying to get it to mess up again. The car is turning over fine, but I noticed some corrosion around one of the battery terminals. I'm wondering if the fuel pump isn't getting enough juice sometimes when its cold, which is the only thing I can think of that would make the pump pressure vary with whether or not the car is running.

Whenever the pressure is in the mid 50s, it starts right up.

I will also probably bite the bullet and change the cap, rotor, and wires in case they are drawing too much current from the fuel pump also.

what a pain in the butt.

[BlazerLT]

Clean the battery terminals.

Check battery voltage with a voltmeter both when off and when the engine is running.

Charge the battery, your battery is low and the pump is not supplying the 60-66psi needed when starting.

Change the cap and rotor and do the obvious things like a tuneup.

[Realitydept]

Originally Posted by BlazerLT

Clean the battery terminals.

Check battery voltage with a voltmeter both when off and when the engine is running.

Charge the battery, your battery is low and the pump is not supplying the 60-66psi needed when starting.

Change the cap and rotor and do the obvious things like a tuneup.

Its 14-something volts when running.

I cleaned the battery terminals and it started right up. After sitting all night it was a very hard start again. Turned over very fast, but didn't light off.

It seems to do better if I just let it turn over a few times, quit, then turn it over a few more times, etc.

It fires right up with the starting fluid.

I'm going to charge the battery overnight and see if that helps. I'll do the tune up on Friday (next day I'm off)

ugh.

[BlazerLT]

Check the battery voltage with a voltmeter, NOT the gauge on the dash.

With the truck running, with the truck off.

[blazes9395]

54 psi is generally needed to fire it up, especially when its cold, like overnight. Anything less than that, you will have a hard starting problem, if it will even start. LT is right, make sure your battery voltage is good with the engine off. get the battery checked and make sure it is good. If your having a hard time starting it, give it a boost and it will likely start up right away. Either way, your hard starting is not enough fuel pressure, you now have to find out whats causing the low pressure.

[BlazerLT]

Originally Posted by blazes9395

54 psi is generally needed to fire it up, especially when its cold, like overnight. Anything less than that, you will have a hard starting problem, if it will even start. LT is right, make sure your battery voltage is good with the engine off. get the battery checked and make sure it is good. If your having a hard time starting it, give it a boost and it will likely start up right away. Either way, your hard starting is not enough fuel pressure, you now have to find out whats causing the low pressure.

Actually, a 1996 CSFI engine requires 60-66psi to start and the pressure is low because of a poor battery, a weak pump, a clogged fuel filter or a bad fuel pressure regulator.

The charge of the battery should be 12.8+ volts when engine is not running and the fuel pressure HAS to min 60psi.

The pump is electric, with a weak battery that needs to be charged, you CANNOT expect it to have the pump prime the system properly.

[blazes9395]

Right, I quoted for the CPI, not your engine, 96 CSFI, I didn't read it close enough. Wow, LT your an important part of this board, cause I don't know who else would put so much time and effort into posting as many posts as you do - good work

[BlazerLT]

I own my own business so I have time to kill.

[blazes9395]

Originally Posted by BlazerLT

The charge of the battery should be 12.8+ volts when engine is not running and the fuel pressure HAS to min 60psi.

The pump is electric, with a weak battery that needs to be charged, you CANNOT expect it to have the pump prime the system properly.

Yes, thats why I recomended getting a boost, it may give the pump the extra push to get it started. It is a little secret we use to use to get the truck into the garage instead of pushing it. It also gave us an idea of where to start with the truck.

[Realitydept]

on Sunday when it wouldn't start, I had it hooked to my son's running '95 Blazer with heavy gauge jumper cables and that didn't help. I didn't see 55psi on the fuel pressure gauge until it started running (after I gassed it with the Ether).

It also would not start on raw gas alone (when poured into the intake) leading me to think I have a weaker than normal spark.

Its a brand new FP gauge, I suppose it could be slightly off, I will hook it to the blazer and see what its reading (it runs fine).

Also, its been progressively getting harder to start, but never refused to fire until after I replaced the plugs, so pulling them and regapping them from .045 to .060 is at the top of my list.

[BlazerLT]

Please, check the battery voltage with a voltmeter when off and when running.