Community Forums

Boujii · 03-13-2018, 02:18 PM

Hello my new friends

I was searching around the forums today looking for an identical problem. But it seems everyone's issue is slightly different.

What I have here is a 1988 Itasca Sunflyer with the P30 chassis. I just bought it for $1500 and the seller said it needed a fuel pump and even bought it. So I put the new mechanical fuel pump in, but it's still having issues. It seems like it's starving for gas. It idles decent. But when you give it any kind of gas, the pressure can either go up or just stall. Most of the time it will just stall.

I've replaced the cartridge filter at the block and the inline filter which is just about halfway the vehicle on the frame.

I was reading in this thread and wanted to confirm that these usually don't have a in-tank pump?
http://www.irv2.com/forums/f258/fuel-pump-382363.html

I was looking about the gas tank and didn't see any wires at all. Though it should have at least the one for the gauge I would think. It wasn't the easiest crawling around under there so I could have missed it.

I did follow the line from the tank to the mechanical pump. I did not find any kind of electrical pickup pump anywhere.

http://75.147.75.181/files/rv/IMG_0317.mp4

The fluctuation in the pressure is when I give it gas.

Any assistance with this would be greatly appreciated.

Thanks a bunch,
Jeff

Edit: This is a Suncruiser not Sunflyer

BFlinn181 · 03-13-2018, 05:13 PM

A GMC P 30 lists an in-tank fuel pump. The mechanical pump doesn't have the suction to pull fuel all the way from the tank and push it to the engine. If you put a fuel pressure gauge into the line between the tank and the mechanical fuel pump, I think you'll find the pressure too low for reliable running. There are many good sources of information online about P30 chassis, they are under thousands of delivery vans, buses, and RVs.

GBDTN · 03-13-2018, 06:39 PM

The older Chevy was notorious for vapor locking and fuel pressures. The fix was an in tank fuel pump and some still had to have an in-line pump to keep pressure up. Drugs from setting, stopping up the pickups, and rubber lines on rop of the tank dry rotting. Had to drop 3 tanks in about 20 years.most chassis were extended and it was cheaper to run rubber.

Boujii · 03-13-2018, 10:33 PM

Thanks for the feedback. I was eyeballing the https://www.summitracing.com/parts/a...olet/model/p30

I was hoping to use something like this as an alternative to dropping the tank and replacing the in-tank pump which I fear may be either bad or just not adequate enough to do the job alone. This pump has 16mm threaded ends which looks like it supposed to replace and mount and existing one. However I am unable to find where this would go since I am unable to locate the original anywhere on the frame.

I would much rather go hose barb and throw it inline if I could. I can contact Summit for an alternative, but I am not certain of the hose barb size on the P30 Chassis. It looks to be either 5/16 or 3/8. I am leaning towards 3/8. Has anyone a better idea then my guessing?

BFlinn181 · 03-13-2018, 11:07 PM

In a 30-year-old RV that has been sitting for a while, dropping the tank to install a replacement pump isn't a bad idea. You could clean it out, replace the gas lines to the motor and the generator, maybe even paint it. Clean the fuel gauge sender and check gas fill hose and any vapor recovery hoses are probably ready for replacement too.

Boujii · 03-13-2018, 11:45 PM

I don't doubt that at all Bob. I am guessing this in-tank pump is called a 'fuel sending unit'?

I've located what I believe is for my 7.4 engine.

Part Number: 3608-09087061
https://www.partsgeek.com/catalog/19...l_sending_unit

I think I am still in the diagnosing stage. If I disconnect the inline fuel filter and turn the ignition key, I should get fuel pumped up to that point from the sending unit correct?

Boujii · 03-17-2018, 02:31 PM

Hello friends,
So before I drop the tank and proceed, I wanted to do some simple diagnostics first. Perhaps someone with experience could assist with this.

Along the chassis there is an inline fuel filter about halfway. I disconnected that and let the metal line coming from the tank sit there with nothing on the end of it. I then turned the ignition to start and gas started to come out the end of the hose. But only while cranking the engine. As far as I can tell, the in-tank pump must be pushing it since it's disconnected before the manual pump at the block.

Gas comes out as long as I can cranking it. But when in accessory mode and after I stop cranking, it stops. I thought that when the key was in accessory mode, it supplies electric to the in-tank pump.

Am I missing something here? If it only supplies electric while cranking, then it will not get gas from the in-tank while running, thus only pumping gas from the manual pump at the block.

I was thinking maybe there is a relay or something else that engages the pump once it's running. I thought it just was engaged the whole time the ignition was one.

Please see the video below. This is me starting it and gas coming out while doing so and then stopping after I let the key off, but still in accessory mode.

http://75.147.75.181/files/rv/video-1521317074.mp4

Thanks a bunch for any input

BFlinn181 · 03-17-2018, 02:46 PM

It's a safety thing. The fuel pump initially gets power for 2 seconds, but if the engine doesn't start, the fuel pump is turned off. To operate otherwise, it could be pumping gasoline after an accident or other reason the engine stops.

If its pumping fuel in sufficient quantity to supply the mechanical pump, it might be O.K. You could look up the requirements of your engine for the fuel flow and capture the fuel as it pumps, paying attention to the time.

MSHappyCampers · 03-17-2018, 03:26 PM

Hi Jeff!

Welcome to IRV2! We're sure glad you joined the gang!

I'm about the farthest thing from a mechanic that you will find, so I can't help with that problem! Keep her between the ditches!

Good luck, happy trails, and God bless!

Boujii · 03-17-2018, 10:24 PM

Thanks Bob, that makes sense about it only supplying fuel while the engine is running. I guess the next step would be to get a pressure tester on it and see what I am getting at an idle and with throttle.

In another thread LJowdy posted "PSI should be 3 to 5 at idle and 9 to 12 at wide open throttle".
So maybe the in-tank pump isn't completely shot yet, but just not doing the job.

Between the manual pump and the electric pump in the tank, I would think that would be enough PSI combined. But hey, what do I know lol?

twinboat · 03-17-2018, 10:32 PM

Try looking for a bad oil pressure switch. It could be used to keep the pump running, when the engine is.

Boujii · 03-17-2018, 11:08 PM

Quote:

Originally Posted by twinboat

Try looking for a bad oil pressure switch. It could be used to keep the pump running, when the engine is.

Good thinking there. I never thought that the pump might not be running when the engine is. Which would give the same starvation symptoms I am getting.

In case others might catch this thread, I found a good read regarding the 454.

454 Engine Fuel Systems Information- Expanded - Engines - FMCA Motorhome Forums

"The fuel requirements for the 454 engine at wide open throttle are 25 gallons per hour at 2 PSI minimum and 3 PSI maximum. If fuel line lengths or
routings create a situation where this cannot be met, an electric pump should be added at the fuel tank to supply fuel to the mechanical pump on the engine."

So I'll investigate that oil pressure switch and the gph/psi.

lonfu · 03-18-2018, 09:14 AM

If it is a carb engine, then I would suspect the accel pump in the carb. Quadajets are tough carbs to rebuild because there are some hidden passages that you have to drill out to be able to clear them. National Carb in florida offers a lifetime rebuild warranty that can't be beat.

If it is a throttle body engine, then I would look at the 2 injectors and their wiring. One injector does your idle and the other does your main load. sounds like one could be plugged or non functioning. I'd replace both, but you can try to clean them out with some carb cleaner. trick to cleaning is to get them to open while you force carb cleaner through them. Youtube has many vids about cleaning injectors.

If it is full fuel injection, and there is no fuel pump in the tank, then you are screwed because you need at least 50psi at the engine to get any action and some one has replaced the engine and not upgraded the fuel system to match the engine requirements.

I'm guessing your have the TBI. I"d also check the "throttle position sensor" if it has one. It can cause exactly the same symptoms that you are indicating. your vid shows that you are getting plenty of fuel. Need to check the fuel pressure at the carb when running. I don't think it is your fuel supply, it is either your TPS or your main injector. When you open up the throttle, the TPS sensor can open and cause the engine to stumble and misfire, even die if it is very severe. The TPS is a reostat or variable resistor. when the computer gets no signal it reduces the fuel to the engine. Checking it when out of the vehicle is not an option because of the way they are made.

The other thing I would check is the dist. cam to make sure that you don't have a worn out cam that is not sparking on the cap contacts.

Hope this helps, I've had all 3 chevy fuel systems.... each one has good things, and bad things about them.

lonfu · 03-18-2018, 09:36 AM

Last year I had to rebuild one carb and replace 16 fuel injectors because I added fuel stablizer to my gas tank. The stuff gummed up every vehicle that I added it to. l Perhaps the last owner added some to the gas tank, that is why I suspect the main injector. stabilzer also gummed up two of the back flow check valves too. Sure learned my lesson....