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  View original topic: Need help with erratic fuel pressure on FI type IV motor Page: 1, 2, 3  Next
bryancald Sat Jun 11, 2016 12:52 pm

I have a stock 77 Westy. I recently installed new (not rebuilt) injectors.
It now feels like it's stumbling ever so slightly at parking lot speeds. I checked the fuel pressure yesterday using the L-Jetronic manual. The pressure is erratic at idle to say the least. To add to possible causes, my EGR filter broke, leaving the lower tube open to the atmosphere. It sounds like this may contribute to the lack of smoothness. I used my phone in slow motion mode to capture what I'm talking about regarding the pressure changes.

https://youtu.be/JHIZakaTekU

I'm leaning towards replacing the fuel pressure regulator, or could the open EGR pipe influence this?[/youtube]

Wildthings Sat Jun 11, 2016 1:10 pm

You can loosen the bolts where the EGR tube attaches to the manifold and using a coin and some RTV silicone to close off the port. If your fuel pressure still fluctuates then check and see what your manifold vacuum is doing, you might just need to do a valve adjustment. Heck just do a valve adjustment anyway.

I would add some FI cleaner to your gas tank to help guaranty that the injectors are not sticking.

SGKent Sat Jun 11, 2016 4:31 pm

pull the vacuum line off the FPR and see if it gets stable. If it still bounces you either have a problem with the FPR or supply side.

bryancald Sat Jun 11, 2016 9:38 pm

Thanks guys, I'll give it a try tomorrow. I've heard replacing a part of the FI can exacerbate other problems. I

old DKP driver Sat Jun 11, 2016 11:11 pm

fuel pressure regulator test.

busdaddy Sun Jun 12, 2016 7:02 am

bryancald wrote: Thanks guys, I'll give it a try tomorrow. I've heard replacing a part of the FI can exacerbate other problems. I
Only without thorough and careful testing, replace nothing until it's been proven bad with science first.

Randy in Maine Sun Jun 12, 2016 7:44 am

Is your gauge liquid filled? (that helps with needle "flutter")

bryancald Sun Jun 12, 2016 11:16 am

When blocking the EGR tube, should I disconnect the valve linkage?

SGKent Sun Jun 12, 2016 12:05 pm

Have you done the tests on page 20?

http://www.thesamba.com/vw/archives/manuals/afc_fi...Manual.pdf

curtp07 Sun Jun 12, 2016 3:10 pm

I was looking at the gauge..Harbor Freight?

CPOC?

Tcash Sun Jun 12, 2016 3:18 pm

curtp07 wrote: I was looking at the gauge..Harbor Freight?

CPOC?

need an item # like this (Item #97706)
http://www.harborfreight.com/catalogsearch/result?q=fuel+pressure+gauge

HFD
Tcash

bryancald Sun Jun 12, 2016 3:56 pm

Test results:

Fuel pump pressure test with regulator vac hose disconnected and plugged.
Ignition on, flapper moved to initiate pump. Result: 38psi

Engine running, regulator vac hose disconnected and plugged.
Result: 37-38psi

Engine running, regulator vac hose connected.
Result: mostly at 28, but will randomly drop to 23-22psi as seen in slo-mo video in original post.

Checked engine vacuum at idle.
Result: steady at 18.5 in Hg

Wildthings Sun Jun 12, 2016 4:02 pm

Maybe you have a suction leak between the tank and the pump?

SGKent Sun Jun 12, 2016 4:12 pm

My money is on the FPR going bad. Reason: the pressure should not vary whether running or not when the hose is off. There should be surplus fuel there to hold the pressure at 38 psi. The pump is always on and the surplus fuel is routed back to the tank. Do make sure that you have an FI tank with a return to the tank on the bottom, and that someone has not put a regular tank in with a tee or something. Also your vacuum source is steady so there is no reason for the pressure to swing that wildly. The FPR is supposed to make very subtle changes as the vacuum in the plenum changes so that the fuel pressure is always the same amount above the manifold pressure. That helps regulate the spray. You can do a volume test on the pump to see if it can supply the correct volume. If you buy a replacement and it is not that then leave the new one on it and keep the old as a spare.

Quote: Fuel pump pressure test with regulator vac hose disconnected and plugged.
Ignition on, flapper moved to initiate pump. Result: 38psi

Engine running, regulator vac hose disconnected and plugged.
Result: 37-38psi

SGKent Sun Jun 12, 2016 4:23 pm

Rock Auto aftermarket $50+/-
http://www.rockauto.com/en/partsearch/?partnum=022906035

Rock Auto genuine Bosch http://www.rockauto.com/?mfr=BOSCH&partnum=0280160200

Amazon https://www.amazon.com/Bosch-0280160200-Fuel-Press...entries*=0

BusDepot - need to call to see what brand $80 http://www.busdepot.com/0280160200

or ebay run the part number "BOSCH 0280160200"

Tcash Sun Jun 12, 2016 4:32 pm

You are going to want to change all your fuel hoses to. They have syrup in them too.
Tcash

SGKent Sun Jun 12, 2016 4:58 pm

Tcash wrote: You are going to want to change all your fuel hoses to. They have syrup in them too.
Tcash

Quote: Ok, was able to get back to the bus after the massive SoCal storm of 2014.

how was this bus affected by that storm? Did it get water, sand, or silt into the gas tank?

bryancald Sun Jun 12, 2016 8:39 pm

Thanks everyone for you help and advice. I have ordered a new valve and will let you know if this was the culprit.

bryancald Sun Jun 12, 2016 8:40 pm

Tcash wrote: You are going to want to change all your fuel hoses to. They have syrup in them too.
Tcash

All fuel and vent lines change within the last year.

bryancald Sun Jun 12, 2016 8:41 pm

SGKent wrote: Rock Auto aftermarket $50+/-
http://www.rockauto.com/en/partsearch/?partnum=022906035

Rock Auto genuine Bosch http://www.rockauto.com/?mfr=BOSCH&partnum=0280160200

Amazon https://www.amazon.com/Bosch-0280160200-Fuel-Press...entries*=0

BusDepot - need to call to see what brand $80 http://www.busdepot.com/0280160200

or eBay run the part number "BOSCH 0280160200"

Thanks for the links SGKent! I found an NOS valve on Ebay for $50.



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