454 P30 ENGINE PROBLEMS

[Daniel Jacobs]

Hi Everyone! I'm having problems with my 1980 Citation p30 motorhome with carburated 454.

A month ago i had a major tune up done on it, changed spark plugs, distibutor cap new battery, alternator etc.  Rv wouldn't start and had to get it towed last week.

fuel filters, fuel lines and fuel pump was changed at a truck repair shop

Today i decided to go for a drive, it ran excellent until 40 minutes onto the highway it started to lose power and backfire when going up a slight hill, i pulled over and at lower speed it seemed to run good again, until i got up to 55 miles it started to backfire and lose power and eventually stalled and would not start back up! I'm guessing the mechanic who worked on it didn't go for a test run after the pump was changed.

I removed air filter to check in carburator and rv cranks good but it's not getting fuel, could it be a faulty fuel pump?

I've been looking on the net for some info on what might be wrong:

Accelerator pump?

Fuel Pressure Regulator?

Vaccum Leak?

Coil?

Intake Valve?

any info would be greatly appreciated?

Thank!

Daniel

[Rick Stafford]

 Hi Daniel,   I just thought I would through in some ideas. Now I am not a mechanic and i am sure there are a lot of fellas on here that know much more then me. But since I have most always for the past 40 years done my own auto work I have had weird things happen through the years  so thought i would comment. I first thought of dist cap because I have had those go bad and as the engine heated a crack will expand and then of corse stall back fire etc.  I have also had problems with the throttle position sensor.  I had a Olds Tornado once that would Idle great you could race the engine and run great but when you went to drive it the thing would not do 30mph. I had it to two shops and one thought timing chain but I did not think so because it started great and all that until I drove it. I spent some time and found it to be the TPS which was mounted in the carb and replaced it and it ran great. Also I would think could be coil. A coil can get hot and loose power. If there is a small break in a winding it makes contact when cool and then acts up when hot from expanding. (Had that problem on lawn mowers too) I just had to replace the coil on  my Astro van because it was doing this. When you say backfire it makes me think ignition but you say it is not getting fuel to carb? Did you try to pour a little dab of gas into the carb and see if it fires?  yes might be fuel pump. If it was me I would pour just a little gas into the carb and see if it fires. I mean to try this if it will not start. Take a spark plug wire off fix stick a screw driver or something into the wire plug and hold it near (close but not touching the block or ground) crank the engine and see if your getting a good spark . Just some old school stuff but common ways. That still work. And yes a vacuum leak can cause problems too. But if I understand you right it stalled and then would not start after warm? Sounds like ignition.  if that coil has many miles on it I would replace it. Oh yeah the rotor can cause problems too.   Like I said Im only giving my two cents worth from my battles with them! Hope I helped a little Best wishes   Rick Stafford

[Daniel Jacobs]

Thank you Rick. I will mention some of this to my mechanic tomorrow.

[Sam Green]

Daniel, try removing the gas cap or just loosen it.  If it is a vented system and the gas cap vent is plugged they will sometimes pull a vaccum and stop the flow of gas.  This may explain why it runs fine cold but later dies out.  If you hear a rush of air when you open the cap that means it is plugged.  I know that this sounds too simple to be true but I also know that it happens.

[Rick Stafford]

 Sam, Thanks for suggesting that. I had forgotten about what trouble that cap can give. my son had a Ford once and it ran terrible due to a plugged vent on the gas cap. So thanks from me as well cause that is good advice I had forgot!

[Chris Reed]

I read through your post and noticed that you had stated, "fuel filters, fuel lines and fuel pump was changed at a truck repair shop". What was the reason for replacing all these items? Did the shop recommend their replacement to solve a problem? If so and there was speculation about something in the fuel system that could cause a drive-ability issue, then why not clean the tank and rebuild the carburetor as well. If the lines, filter(s) and pump were replaced to cure a problem, the problem would have to start somewhere (the tank) and after passing through the system will end up somewhere (the carburetor). Given that at some point your filter(s) allowed enough of the contaminant to pass through the system to cause an issue. If this is a suspected problem you could install a clear glass filter inline and try to start the engine and see what you get in the filter. Just a couple of thought, if I had a suspected fuel system issue I would do some more diagnosis to accurately diagnose the root problem before throwing money at it. The comment by Sam Green was an excellent idea and simple to check, too.

[Richard W. Cobbs]

Hi, Many years ago I bought a van at a substantial discount because it had a similar problem.  The owner had spent a lot of money at several mechanical shops, but they didn't solve the problem.  I was able to track down the problem to a rubber fuel line that connected from the tank to the steel fuel line that runs along the frame.  Someone had installed a line that was too long and as it got older it would collapse from the vacuum created by the fuel pump.  It would start and run for a while then stop until the vacuum drained off, then start again and run till the vacuum collapsed the line again.  I had to drop the tank in order to install a new flexible fuel line.

[Mike and Heather Brancich]

Daniel, My name is Mike and I am a retired Auto and Diesel Technician, I also worked on a lot of Motor Coaches when I co-owned a shop.  One of the things I have always done is put an electric pusher fuel pump on the frame rail as close to the fuel tank as possible. The Manuel fuel pumps that are being built now days "suck". they wont pull any more than a 2 inch vacuum. that is why I run a electric fuel pump The best pump I have found and always used is a MR GASKET pump from Oriely's. The part number on their website is 12S, It cost around $50.00. This is what I am running on my 1974 Dodge Travco and my lean out conditions have ceased. I have also found that a cold air intake helps even more. The reason for the cold air intake system is that hot air from the engine being sucked into the carburetor will cause a lean out condition also referred to as a vapor lock. this is where the fuel is evaporating before it has a chance to reach the engine. I also like to run clear style fuel filters, that way I can tell if the fuel is reaching the engine. If you have any questions reply and I will try to respond. 

Sincerely Mike 

[Alan Cookerly Sr.]

Mike-don't want to hi-jack this thread-but I have been thinking of installing an electric pump in my M40 Dodge Chassis-440 eng. I haven't had any starving yet, but after sitting for more than 2 days-I have to manually fill carb float bowl to get a quick restart-Did you run thru the manual pump or bypass it?-Thanks-Al

[Richard W. Cobbs]

Alan, pull your dipstick and smell your oil.  I suspect that you will smell gas in the oil and that your carb is leaking into the intake manifold after shutdown.

RWC

[Alan Cookerly Sr.]

Richard-Thanks for the reply-I was working in mechanics during the Thermo-Quad era. Even learned how to replace the seals under the bowls & cracked bowls. Even tho this may leak down (I'm not convinced of that yet) it won't fill the bowl back up with cranking-you can run the battery down trying-but if you fill the front bowl thru a vent tube-it starts right up at runs smooth. I guess I wanted the elec pump more for that-just wondered if I could be lazy and run it thru the existing pump.-Thanks-Al

[Jim Sweet]

I had the fuel guage problem and got into the tank and found the electric fuel pump which I did replace. Got my help from the Forum and it all worked. The other problem of the engine  cutting out was also solved. So with the 89 P30 with the 454 needs the in the tank pump.

[redwing]

well first let me say i hope for better days, i should let you know we have a yahoo group for p-30's thats pretty extensive and only deals with that chassis.

 

your describing a problem that has been known in the industry for a long time (2000) it has to deal with the distance that the fuel has to travel from the tank to the engine, this creates a big suction and since your rig is an older rig i going to point you at a few culprits, there are two places that causes problem the first one is the pickup hose between the tank and the main line and the second is the hose between the pump and suction line, both of these hoses unless changed after the introduction of alcohol into fuel in the year 2000 will soften the hose up to the point that suctiion closes it off. sure they may have replaced most of the line, but unless they dropped the tank and replaced that hose thats where to start, most likely with a new fuel pump the front one was changed.

 

another note is if the tank is in the rear of the motorhome and not in the front, you also have a pump which can not pull fuel that far and by the time it does it can't provide enough fuel for full throttle under load. this too was a problem for the p-30. and the fix was a vane pump like will be in the pdf below.

 

i'll leave a pdf url below which deals with not only vapor lock(not your problem) but also deals with the fuel delivery problem from a rear tank.    redwing

 

http://truckroadservice.com/barth_attachments/Chevy_P32_vaporlock.pdf