'94 Ram Van issue...fuel pressure regulator?


motoguy
12-14-2007, 11:11 PM
I've got a '94 MaxiWagon, 360 auto. ~225k miles. The fan will usually start fine when cold, but I have problems after it's warmed up. Once the van is warmed up (say, after driving it for 15-20 minutes), I have re-start issues.

Basically, I have to crank it 6-7 times (for a decent period) to get it to start. It's a progressive thing...first crank nothing, by the 3rd it's trying to hit, by the 5th it's almost started, and on the 6th crank or so...it fires up.

I thought it might be the fuel pump, given the age and mileage on the van. I had a buddy swing by with a fuel pressure gauge, and we checked it out. Upon turning on the key, the pressure spikes to about 45psi, then drops back down to 0. Upon cranking, the pressure goes back up to ~45 psi. When running, it stays at ~45psi. Upon shutting the van off, though, the pressure drops -immediately- to 0.

Any ideas what this may be? Would a leaky injector be able to drop the fuel pressure almost instantly? Would that somehow be the fuel pump, even though 45psi seems to be in line with the manual? Fuel pressure regulator?

I'd love to get some input from those who know more about it than I do! :)

alloro
12-15-2007, 12:39 PM
The fuel pressure is fine since you're getting 45 psi during cranking and running. I'd focus on the coil, distributor, plugs, or wires first. Have you checked for good spark when the van doesn't start.

motoguy
12-15-2007, 01:19 PM
The fuel pressure is fine since you're getting 45 psi during cranking and running. I'd focus on the coil, distributor, plugs, or wires first. Have you checked for good spark when the van doesn't start.

Thanks for the note! According to the information I could find online, after shutting off the van, the fuel pressure should slowly bleed off over a period of time. Minutes, to tens of minutes is how I understood it. When we shut of my van, the pressure -instantly- drops to 0.

My friend was of the opinion that when the pressure drops to zero, the fuel in the lines may begin to boil (or whatever). He thought it felt like a vapor lock issue. He said normally the slow-bleedoff of fuel pressure would keep this from happening, but my instantaeous drop may be allowing it.

Ideas? I'm not trying to be argumentative...but the van doesn't give me issues in any other way. No issues while driving, under load, etc. I would expect electrical issues to act up at that time (particularly a coil issue while under load). It just "feels" fuel-ish to me...if that makes sense...

alloro
12-15-2007, 05:18 PM
Your friend's idea of the fuel boiling is imaginative but highly unlikely since the fuel is not near a heat source as is the case with a carb. The quick drop in pressure is not going to do this unless the line goes from being pressurized to having a vacuum. There is a check valve in the fuel system that is supposed to slow the depressurization of the fuel line. It sounds like that might be leaking. It's a part of the sender unit in the tank.

I mentioned the coil because it is a distinct possibility that it's efficiency drops off as it becomes heated. Others have reported this same problem and the coil was the culprit. Keep in mind that the coil can be receiving 40% more power when the engine is running versus when the engine is being started.

During cranking, you're loading down a 12v battery to as low as 9 volts, but when the engine is running, the voltage can be up around 14 volts. A weak coil will not work during the lower power moments, yet function normally with the higher voltage. It's best to pull a plug wire and check to see if you're getting a strong blue spark or a weak orange (or non-existent) spark during these no start periods.

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