Slow To Start; Fuel Pressure Related?

[brplut40]

I have a 1998 GMC K1500 Z71 with a 5.7L V8. It has the throttle body injection. My truck is not my daily driver, so it tends to sit for about a week at a time. When I go to start the truck, it sometimes will take a long time to start. The oil pressure takes about 2 seconds to build up, which I verified with the dash gauge. A couple of weeks ago I had to crank it so much, the battery died. After I charged the battery for a couple of hours I tried again, and after a minute or 2 it finally started. When I go to start it now it, I will have to crank it on and off for about a minute until it will fire. Reading some things on this forum, which is very helpful, I think it may be fuel related. I got a hold of a fuel pressure gauge and noted the pressure at various times. What I am wondering is if these pressures look low, especially during cranking?

 

When I turn the key to the on position, I can hear the pump come on for 2 seconds and the pressure goes to 56psi

After 2 minutes the pressure dropped to 52psi, and looked like it was continuing to slowly drop

On first crank the pressure dropped to 44-46psi while cranking

When I stopped cranking it went back to 56psi

Second crank went from about 46psi until 50psi which is when it started

While running the truck maintains 52psi constant

 

Is this a bad fuel pressure regulator? Can anyone give me what these pressures should be? Any other test or ideas?

[silveradocoa]

those are good pressures. take a fuel sample and see if it smells right or was crap in it. just to cover the standard stuff look at your plugs and wires

[brplut40]

Forgot to mention that I replaced the plugs in the last 3 months and replaced the fuel filter in late Dec. I have not checked the wires lately, but they, along with the cap and rotor were all replaced 4 years ago.

[markw8]

This sounds fuel related rather than electrical. Mark.

[brplut40]

update in this situation. I decided to pull the cap and rotor off to look at the condition of them, just to make sure. According to Chiltons' if there is anything other than infinite resistance across all the connections on the cap, it should be replaced. When I pulled the cap off, it was corroded and did not look very good. There was almost 2 ohms of resistance between the connection point for the rotor and coil wire. I replaced the cap and rotor and everything runs much better. The exhaust sounds like it is fully there when I accelerate and idle. It starts easier also. It was cool and raining yesterday and it started right up.

 

When I opened the new cap a piece of paper fell out of the box. It was a note saying that there was a special technical bulletin. GM TSB #03-06-04-041A and #05500 state the distributor cap and rotor may be subjet to premature corrosion and ignition system failure due to a lack of airflow internal to the cap. GM recommends the following corrective actions:

 

1. inspect and clean the 2 distributor vents located in the base of the distributor housing. later model vehicles were equipped with a distributor base manufactured with vent screens. the screens should be removed to improve airflow.

 

2. some vehicles may have and air conditioning accumulator line near the distributor base. GM has recommended insulation of the line to prevent transfer of accumulated condensation to the distributor base vents. the required foam sleeve should be 9.0 inches in length, have an internal diameter of 1.125 inches with a thickness of .250 inches.

 

3. visually inspect to ensure that there are no coolant leaks. check heater hoses and areas surrounding the intake manifold.

 

4. ensure the PCV system is operating correctly, and is drawing moisture from the crankcase. the moisture can travel up the distributor shaft into the cap. Engine oil should be changes on schedule to prevent moisture as well.

 

5. inspect the distributor rotor condition,a nd replace as necessary.

 

I guess it was electrical related. $60 solved the problem.

[Gert]

*****************

I have a 97 Astro with the same or similar problem. In my case it's all electrical. I've been chasing this for 3 years. My final solution to get it back on the road is to change the Cap & Rotor every time it starts to misfire / stumble. I've gone thru 5 Caps now. Here's a bulletin I found from NAPA that explains it.

http://www.napaechlin.com/web_app/DYK/down...Distributor.pdf

As of yet I have not found a Cap brand that works more then 8 months. I have tried Delco, Standard, NAPA, and some off brands. Hope this helps!

[brplut40]

Well unfortunately I must revive this thread. Once again my truck is VERY slow to start, if it does at all. As you can see from the previous post, I changed the cap and rotor 3 months ago. I am really hoping it has not gone bad that fast. Is it possible for someone to provide or link to detailed instructions on how to test various fuel components. I would like to ensure that the fuel pump, especially the check valve, fuel pressure regulator, and injector is functioning properly. I know there are a wide variety of things to test for the fuel pump including the relay and the oil pressure switch. If anyone can please provide directions or links on how to do all or any of these it would be appreciated. I am really starting to get sick of being ready to going boating and the truck not starting.

 

One last thing. I have been ready some on the oil pressure switch and tried something out. When the truck was running I disconnected the connector from the oil pressure sending unit. I verified I had the correct sensor by looking at the gauge on the dash. The gauge read nothing. I thought the truck would stop if I disconnected this but it did not. am I wrong in that once the truck is started, power for the fuel pump runs through the oil pressure switch to verify there is oil pressure. I figured when I disconnected the switch, the system would see no oil pressure, and stop sending power to the pump. Where did I go wrong on this?

[brplut40]

anyone know what the cause is if the truck will start after adding a little starting fluid? runs fine once it kicks over and gets going. Does that mean the injector is clogged a little, the fuel pump is creating enough pressure when cranking, bad fuel pressure regulator, etc???

[BigBlaze]

random question... with key on engine off, will it hold fuel pressure or does it bleed down?

[BigBlaze]

never mind, just read your first post......

[BigBlaze]

you can use a noid light to check the electrical side of the injectors. you can also use a logic pulser and a fuel pressure gauge together.... use the logic pulser to pulse the injector, and watch the fuel pressure as you pulse the injectors.(checking for a clogged or leaky injector)

[brplut40]

I don't know a whole lot about fuel injection and throttle bodies, so maybe someone can help. In a throttle body injection, TBI, which is what I think my truck has, there is a throttle body, which looks kind of like a carb, that has a single fuel injector in it, instead of barrels. Is this correct?

 

Should an injector be clogged after 116,000 miles, even if I use a fuel injector cleaner every 3,000 miles or so?

 

Would running performance suffer if the injector was clogged to such a level that the truck has extreme difficulty starting? Or can the PCM adjust the pulse enough, that even if the injector is clogged, it will run fine?

[BigBlaze]

lots of short trip driving, followed by a long heat soak can cause an injector to clog... and yes your truck has an injector under the throttle blade.... btw, all good gas companies such as shell, exxon, bp, etc. already contain more than enough detergents to keep your fuel system clean.. (for example, chevron with techron... you can buy techron at advance auto, but their fuel already contains it)

[brplut40]

Well I finally solved this problem. It was the Fuel Pump. I looked at the fuel pump specs in the manual and it stated that with the key on, truck not running the fuel pressure should be between 60-66psi. As I stated in my first post it was 56psi. Because fuel injectors are so picky, especially when first starting, 56psi was not enough pressure. So I dumped the tank, replaced the pump and it starts right up now. So glad I finally got this solved, especially before winter gets here.