Code P0300

Good evening,

What is the fuel pressure? Low fuel pressure is the most common cause for this code.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

You have covered most of the basics. but the fuel pressure should have been the first check.

Did you do a compression test when you had the plugs out?

https://www.2carpros.com/articles/how-to-test-engine-compression

Roy

The fuel pressure was the second thing I checked after the cap and rotor. It was excellent.
Did not check the compression because the Astro van is a nightmare to work on, especially on your back on the floor. The truck ran perfectly, until whatever failed messed things up.

What is the exact fuel pressure? I need numbers to help.

Roy

I am almost positive it was 65 lbs. I will pull the doghouse today and confirm. I have had no less than six fuel pumps replaced on my 1996 Astro! So I wouldn't doubt that it could have been the cause. I had to cut a hole in the floor of the truck to get faster access to the pump for replacement. Saved dropping the tank each time. The truck coughs and stumbles starting up from a stop until I give it more throttle! At higher speeds it runs fairly well until I let up on the throttle a bit, then it stumbles (misses). I hope the jpg with the fuel trim data helped. I will reply again once I pull the dog house and take another reading to the fuel pressure.
Wayne

Thanks Wayne.

I will be looking for the fuel pressure readings.

Roy

I am glad I rechecked the fuel pressure! Turn on key, pressure goes to 65 lbs! Then immediately falls to 57-58 lbs! Book says it should be between 58-64 lbs. Would you suggest replacing the fuel pump? It is a bit messy, but if you say yes, I will cut through the floor above the tank and replace the pump! I've done it before on the 1996 and it is the best way, especially, if I have to do it again down the road.

Thank you very much,

Wayne

Yes sir. You need a fuel pump.

Roy

Just one more thing, since about ten to fifteen minutes ago when I took the readings, the fuel pressure dropped to 51lbs. With a new spider injector system installed, it must be flowing back into the tank. Your guess?

Yes, the check valve in the pump is the issue. that is why you are replacing the pump.

Roy

Thank you very, very, very much for your help!
Wayne

Never a problem.

Roy

Roy,
Well, I just replaced the fuel pump on the Astrovan which was less than a pleasant experience. With the new pump, the pressure hits 63-64 lbs and then immediately goes to 58-59 lbs which is at the low end of he 58-64 lb range the manual says is OK. That is only 1 or two lbs more than the pump that was in there. Then, the pumps pressure falls to 50 lbs in about 10-15 minutes. No gas is escaping from the repair. The spider injector mechanism is new and tested for leaks during assembly. Where else could the pressure be leaking to? I am at a loss....so much money time and effort. I haven't taken it out for a test drive yet, but I would expect the same jerking and error code P0300 misfire. Any suggestions would be helpful. I don't know if you still have the info from my live data, etc.
Wayne

Monitor the fuel pressure while driving and see what the actual pressure is while driving.

Roy

OK, but I have to keep the dog house off and it's cold outside!!!
I'll check it out.
Thanks

Sounds like a plan

Roy

Could I get an accurate reading by just putting a hose on the exhaust pipe and putting that out of the garage and bringing the rpm up to 2 or 3 thousand? Or, should I take it out on the highway?

Just normal driving around town. No 60 mph.

Looking to see what it does under load.

Roy

OK, I will have to do that tomorrow.
Thanks Roy

Your welcome

Always glad to help

Roy

I don't see my earlier reply message here, so I'll try to remember what took place on my little test drive. At 30mph in OverDrive, the fuel pressure maintained pretty close to 58-59 lbs. As I increased speed to about 40, the pressure went up to about 60 psi and then settled back to about 58-59 lbs. Using 2nd gear and low speed (about 20 mph) the pressure went up to around 62 lbs while coughing and jerking like crazy. Then the pressure went back down to about 59 lbs when no longer accelerating. The truck is acting just like it had from the initial P0300 code and all the stuff I've replaced like: Spider Injectors, Distributor Cap and Rotor, Plugs and Wires, and now Fuel Pump. Any suggestions besides setting the truck afire!
Wayne

Did you try disconnecting the egr valve and driving it

Roy

No, I did take it out and made absolutely sure that it was free and clear of any carbon buildup. Replaced the gasket. I will try to disconnect it tomorrow and take it for a spin.
Wayne

The reason I ask is back pressure from the cat converter.

OK, just returned from the test drive. It might have made a very slight difference. Hard to tell. In 2nd gear still bucking and coughing a little with and without hooking up the EGR valve. In 1st gear at 15mph you get one hell of a ride...coughing and jerking like you wouldn't believe!

Check the back pressure on the cats.

Roy

New for me, how do you check for the back pressure????

Use a back pressure gauge in where the o2 sensor goes and run the engine. No more than 1 5 lbs.

Roy

I can order one on line that has an adapter that looks like it would fit in where an 02 sensor goes. May take a few days to get it. I was wondering if my compression gauge used on the cylinders would work and have the proper adapters?
Wayne
PS: Were you referring to run the engine no higher than to generate 15 lbs of compression or 1.5 or ??? I thought that there was to be no compression if the Cat isn't plugged. I also noticed that on youtube that had that problem......The vehicles couldn't get power, where mine had no problem getting to 70 mph. Open throttle and it flys.

Sorry, I meant 1.5 lbs. Senior moment.

Your compression tester gauge will not read that low.

Roy

Ordered gauge...Due here around the 1st of Feb.
Any idea of what else to check while I am waiting? I would hate to go after a compression test on the engine. Everything is so hard to get at on this truck.
Wayne

You can do just one cylinder to see what the compression actually is.

Roy

Roy, How are you on 2001 Ford Expedition vacuum line routing?
I have a disconnected hose and do not know where it plugs in.
Should be easy, but I just can't find it.
Let me know. I have enclosed a couple of photos just in case.
I think I have the white hose correct, It is the red one that I can't find a home for.
They both come out in a harness from the passenger side of the engine around back to the driver's side.

Wayne

OK, We are on a new vehicle.

Site rules are 1 vehicle per post.

Please start a new request and we will be glad to help you with this issue as well.

Roy