My Cold Start Problem

[ZZ]

I have a 1990 GMC Sierra 4X4 Ex Cab that has developed a cold start problem for the 2nd time in 5 months. The 1st time was last September and then only if the outside temp dropped below 45 degrees. It was like it was losing prime. It would start easy and then only run from 5 to 7 seconds. Then I'd have to crank it several times to get to prime back up. Then it would be Ok till it sit overnight. A fuel filter change cured the problem till about 2 weeks ago.

One day it was fine and the next it was back to starting and then stopping after a few seconds again. I changed the filter again, but it didn't cure it this time. The next morning it was like it was out of fuel. I know this was wrong but then I by-passed the oil pressure switch to the lift pump. That helped a couple of mornings and then it was back again. Yesterday I put a new lift pump on it hoping that would help. I went to the hospital earlier tonight and it was parked a little over 4 hours. It started this time and ran from 10 to 15 seconds and then died. I seems I had to had to crank it quite a bit longer with this new $64.99 Carter lift pump from O'Rielley's Parts Store.

I guess it is somehow leaking the fuel back to the tank. I've had the truck for almost a year. The only leak I've seen is under the back of the engine if I cram the fuel tank too full. The IP is dry and the throttle shaft is not leaking.

I'm not convinced the fuel is leaking from the IP pump since it will usually run a few seconds.

Any ideas will be greatly appreciated....

[britannic]

Check out the troubleshooting section in the reference section and look up IP drain back; the earlier lift pump and IP didn't do a good job of preventing this problem. As the temperature drops, the fuel contracts and starts to siphon back towards the tank, whilst drawing air from the return line past the IP return check valve.

GM updated the mech. lift pump with ventless check valves and an anti-siphon design in the IP return check valve.

I had exactly the same symptoms you describe, until I installed the anti-drainback lift pump and valve. Earlier, I had installed a leak free fuel filter housing (the drain valves on the FM80 can be a real pain) and fixed an air leak in the fuel line feeding the lift pump which stopped the symptoms somewhat, but as the weather grew even colder, they worsened again.

To fix this issue, first eliminate all air leaks from your fuel system (tip: pressurize the fuel tank with 8psi using a modified fuel cap with a tire valve and then check for seepage in the fuel lines to the lift pump).

Then install the updated components: fuel lift pump with ventless check valves is P/N 25116503 and the updated return check valve is P/N 10149645.

[ZZ]

Thanks. I'll check into the mods you talked about this week. I could not find the IP leak down you talked about that is supposed to be in the reference section. Is the valve you spoke of on the IP internal or external?

[ 01-25-2004, 08:00 AM: Message edited by: ZZ ]

[britannic]

Look under the heading Fuel Lift Pump in chapter 2 of the Troubleshooting Guide (http://www.thedieselpage.com/members/guide2.htm). The IP regulator check valve is external and very easy to replace.

[ZZ]

Thanks again. The new lift pump I put on it yesterday should be Ok according to the article. I will order the check valve online today. I found it on gmpartsdirect.com for $28

[ZZ]

Nothing has worked yet. It evidently has a leak. The smell is too strong and there is spots under it on different nights. It is going in the shop in the morning. I told them to find the leak and fix it.

[ZZ]

The truck went in the shop Friday. The drain hose that attaches to the bottom of the drain valve by the thermostat housing was loose. It started like a new one Saturday morning. It's Hell when something that simple causes such headaches.

I also changed it over to the LDM glow plugs yesterday. They seem to be working well. They are not exact replacements, but are stamped 11 volts like the AC-60G. A couple of them were rough getting threaded. A 10mm socket is used instead of 3/8. I sure hope they don't swell much if they ever fail.