'96 Jimmy hard start

[blazes9395]

Originally Posted by 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).

That rules out being a low battery condition if it was being boosted and it still didn't work.

[Realitydept]

Originally Posted by blazes9395

That rules out being a low battery condition if it was being boosted and it still didn't work.

I had the battery load tested, it is fine. The starter spins over super fast, also. I tried a booster box just for grins and that didn't help either. I cleaned the battery terminals, etc, nothing changed.

Today I pulled the plugs, regapped them to .060, changed the wires, the cap and rotor. I changed the air filter last week. Its still doing the same thing. 45 psi or so on the fuel pressure gauge when its been sitting for a while, and 55psi while running.

Where is the fuel pressure regulator?

[BlazerLT]

Originally Posted by Realitydept

I had the battery load tested, it is fine. The starter spins over super fast, also. I tried a booster box just for grins and that didn't help either. I cleaned the battery terminals, etc, nothing changed.

Today I pulled the plugs, regapped them to .060, changed the wires, the cap and rotor. I changed the air filter last week. Its still doing the same thing. 45 psi or so on the fuel pressure gauge when its been sitting for a while, and 55psi while running.

Where is the fuel pressure regulator?

Tell me this, what is the battery voltage when the engine is not running.

AGAIN, take the voltmeter out there and CHECK IT!!!!

Just because the engine won't fire off of a boost does not mean that the battery is fine.

If a plate has let go in the battery, it won't accept a charge either.

[Realitydept]

I don't have a DVM handy, but the parts store insisted the battery was fine. Its only about 18months old and is warrantied, so I doubt they're lying to me.

Anyhow, I will swap the battery with a known good one from my Blazer and see what happens before tearing into anything, but...assuming the battery isn't the issue, would you agree that the fuel pressure regulator is the next likely culprit?

[Realitydept]

hi, folks, I'm running out of ideas. I checked the battery today. I've got 12.7 volts not runnint, 13.9 when running.

I swapped the battery from my perfectly running Blazer just for grins and still have 45 psi on the fuel gauge when you key it on.

Once the car fires, the fuel pressure goes to 55psi. Keep in mind that this fuel pressure gauge is a cheap-o from Advance Auto parts, but it is consistent.

When the gauge shows 55psi, it will start every time.

When I turn the key off, the fuel pressure does not bleed down for 15-20min, which means that the check valve in the pump may or may not be ok, but for sure it means that I don't have an injector leaking so bad that it will prevent the fuel pressure from holding.

So, I think I either have a bad fuel pump or a bad fuel pressure regulator. I'm leaning away from the pump, because when the truck runs, it makes enough pressure to restart and it also has good performance otherwise, not sluggish, not jerky, etc.

I have to pull the upper plenum and injection to replace the regulator, which I will likely do tomorrow unless I get some other ideas here. Anyone?

[BlazerLT]

Swap in a new fuel filter.

Also, you should have 60-66psi with the key on but the engine not started.

Could be the regulator or the pump, or a blocked fuel filter.

[Realitydept]

the filter is brand new (week ago as part of troubleshooting this problem).

So, is there any way to best guess this one, or should I just start swapping parts?

I'm leaning towards the regulator, as there is no reason the pump would pump less psi with the engine not running.

[BlazerLT]

I would get the battery load tested becuase if it is not putting out the right current, it might cause the pump not the prime the system enough.

[Realitydept]

Originally Posted by Realitydept

the filter is brand new (week ago as part of troubleshooting this problem).

So, is there any way to best guess this one, or should I just start swapping parts?

I'm leaning towards the regulator, as there is no reason the pump would pump less psi with the engine not running.

I had it load tested in 22 degree weather and the shop said it was fine.

plus, today I swapped it with another good battery and the symptoms didn't change.

[Realitydept]

Just for grins, I went out just now and bypassed the fuel pump relay (conneced the test wire to 12v and got 60psi on my gauge. When the relay kicked in when I turned the key, it actually lost psi.

I'm going to try swapping the relay in the glove box w/ another one and see what happens.

ugh.

[BlazerLT]

Welp, smart thing will be to work from the cheapest part to the most expensive.

It could indeed be the regulator.

[JackDaniels386]

well, if you bypassed the relay and got 60 PSI, it has to be a wiring related problem. If its not the relay, get a meter and check the voltage in the circuit. My guess is that theres too much resistance in the circuit and thats not giving ur pump the juice it needs to turn fast enough to get you at around 60 Psi. it could be a bad ground.

[Realitydept]

Hi, everyone.

To pick up where we left off, I hotwired the pump with the underhood wire and left the wire connected for about 30 seconds, and the pump eventually got 60psi and the truck would start. This eliminated the fuel pressure regulator as the culprit, as well as the electrical parts.

The remaining possibility was the fuel pump, which I had swapped, and that fixed the problem.

BIG HINT: employee cost on a new pump from GM is around $250. There are some wholesalers selling new pumps on Ebay for $175, which is the route I took. I also shopped around and had a local shop swap the pump for $150, which was about $80 less than the dealer wanted.

Thanks for all the ideas from everyone, its nice to have a running truck again.

Ed

[brucexxx]

I have a 94 S15 Jimmy that has a similar problem. Hard to start after about an hour. Less than an hour and it starts right up with a tap of the key. Even if the motor is still warm will struggle with starting if sets for more than an hour or so. Worked perfectly up to a couple weeks ago. Will start but will crank for awhile before it does. Some black smoke for a few seconds and then it levels out. From what I can see from the forum it might be the fuel pump or the fuel pressure regulator. Can I check the fuel pressure right from the port right before it goes into the intake manifold ... I think that is what this port is for...

Sounds like i better get 60 PSI right away or there may be an issue with the pump or the filter located on the frame mid way down the truck on the drivers side? I have never replaced this but have a new one ready. Vehicle has 96K on it right now. Seems to run well otherwise. Just replaced the Cap and rotor and plugs ... made no difference at all

Help.....
Thanks
Bruce

Originally Posted by 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