Bruno DeSousa

got it mark thanks. i was measuring vacuum because i was unsure if the FPRs were not getting enough vacuum to operate correctly.. i understand that the fuel pressure test port is on the rail.. thanks again..

just to clarify.. the manifold vacuum when under acceleration increases in order to open the FPR diaphragm to allow fuel pressure to increase or decrease? im a little confused as to how a FPR actually works.. i thought the fuel pressure decreased when the diaphragm in the FPR opens.?

thanks guys!

mark kibort

the vacuum is there during idle or off throttle , to reduce the fuel pressure.. might go from 35psi to 30psi ...... thats manifold vacuum. you floor it, that vacuum trys to go to 0.... you have a turbo, that goes up to 7-8-5psi, depending on boost levels. you get the idea.

it has little bearing on the fuel regulators. there is a valve in the fuel regulator that is spring operated an that regulates the fuel that returns back to the fuel tank... if all the fuel was routed back, there would be no pressure, if none, then very high pressure...... some, well, thats what we have ,and that pressure is about 30-50psi depending on the model.
it (and the pumps capacity) determines the fuel pressure, nothing else.
regulator itself regulates the fuel pressure. the more that is needed, the less that returns back to the tank. if you are idling or engine even off and fuel pump jumpered, the pressure is regulated by the regulator and its internal set of a spring and a valve.

do a search on fuel pressure regulator and you can see the diagram..pretty simple . thats why the rising rate fuel regulator is so effective...you can set that spring pressure and raise and lower pressure. (crude, but VERY effective for the Ljet cars especially)

Bruno DeSousa

ok now im starting to get it!! well my running rich issue would mean the FPRs would be closed shut correct? causing minimal return fuel to the tank = higher fuel pressure at the rails = running rich.

is there any way to physically test the FPR with it off the car? i tried pumping the vacuum gun to 20 psi and it held pressure then tried to blow from the inlet and outlet of the FPR(holding my finger over the opposite side i was blowing in to see if any air would escape through the return to tank line and there is nothing coming through.. or are my lungs to weak to move the valve.. the car sat for a while and perhaps the old gas glued the valved closed? i know the PO had to replace the filter and pump just to get gas to the rails..? im learning a lot!!

also wanted to mention that one of the Previous Owners or someone at one time put the - jumper cable on the + engine bay jump post and the + cable on the chassis causing the front engine harness to burn up badly.. alternator burned up and now im wondering if this might have fried the spark box causing a horrible firing order. the car does misfire .. this could also explain the running rich issue.. hmmmm

hwyengr

I'm still not sure why you're so certain that the problem is with the FPR. It's much more likely that something is wrong with the L-Jet, causing it to keep the injectors open longer than needed. Go through Hacker's list earlier up-thread. That's good advice, there.

Mrmerlin

Please write down the numbers of the parts and the locations of the parts,
From your info its quite possible you have a FPR swapped with a fuel damper.

NOTE they look the same.

Bruno DeSousa

Ive already swapped LJet with a good unit and no change. Ill check the part numbers but i think they are original FPRs the car has 43k original miles. Just sat in a garage last 10 years

Mrmerlin

posting pictures of the parts would also help,
though you have to have a membership to post pictures

hacker-pschorr

Did you read my post?
It takes less than a minute to test the temp 2 coolant sensor with a multi-meter and they do fail.

Bruno DeSousa

yes i read the post.. ive tested the temp sensors and everything else for continuity.. the L-jet brain plug and all... im past that easy stuff.. narrowed down to either stuck FPRs/clogged return line/ignition control unit/distributor/coil... everything else has been tested and sorted.

mark kibort

you are on the right track in understanding how the system works, but its probably near impossible that the rich condition is due to a "stuck" fuel reg. pressure woud go near 100psi if that was the case. ive got the S4 RRFR to go to 72psi, but the fuel mixture is really metered by the 02 sensor, in closed loop mode. the injector duration will be minimal and keep mixtures good. then at WOT, open loop, the fuel pressure and fuel maps take over and you could be overly rich at that point and nothing can be done about that but fuel pressure reduction.

how do you know you are rich? stop messing with the vacuum, as it does almost nothign.... sucking on the lines is only about 2psi, that will have no efffect on the fuel pressure that you can measure of see. its all about line pressure and you need a guage to measure that.

mark kibort

yes, and they fail after rebuilds when the wrong connectors are connected, as the two sesnsors look alike and cause one to short out and melt the sensor, causing very rich condtions. i think the ohms is something like 1000 ohms, otherwise this is a mixture problem. I think when the ohmes were tooo high, there was no fuel, and i remeber starting the car by wedging a screwdriver in the AFM to provide fuel to start, proving that it was lean. however, a new sensor fixed it .

hacker-pschorr

Have you pulled the plugs to see if the mixture is consistent across all 8 cylinders?



It's a range, and all three ranges need to be tested. I've had Temp II sensors "stuck" that caused either a rich condition or a super lean cold start.

From the WSM:
-10C / 14F; 7,000 - 12,000 ohms
20C / 68F: 2,000 - 4,000 ohms
80C / 176F: 250 - 400 ohms

The higher the ohms the richer the mixture. It's consistent and fun to play with by connecting a potentiometer to the harness. I did this years ago with my supercharged 81 when playing with different tuning setups.

That's not the only way the fail. As noted above, you can have a sensor that tests out fine when cold, during warmup.....but never reach the full lower resistance for a warmed up engine which will run rich.

They can simply "wear out" with age. It's something that should be checked annually.

Zero ohms means no fuel (car will not run or shouldn't run with this sensor disconnected)
Too high ohms will be super rich.....if it's really high will flood the engine into a no-run condition.


Bottom line, if a temp II sensor is above 400 ohms when fully warmed up it will be too rich. Even close to 400 could cause issues. At one point when my 81 was always running a bit on the fat side, I gathered up 5 sensors, tested them all in 200 degree water and installed the one with the lowest resistance.

The best way to test is at the harness end going to the L-jet to take up any variable of bad wires and / or someone adding a resistor in-line with the sensor.

mark kibort

i had it fail by misconnection , can happen after an engine install. so, it can fail this way FOR SURE.

yes, you are right..... the temp to melted and became 0 ohms, and that was no fuel.. thats why the AFM trick worked with the screwdriver to get it running to add fuel based on barn door position..

i also installed a 2000ohm resistor based on the 3 ranges you noted, and got it running. that proved in our case, (scots car) that the temp II was melted and had 0 ohms. good first check for sure to get out a meter and check it. might be something simple like this

Bruno DeSousa

my temp II sensor was reading under 400 ohms with warmed up motor on a 85 degree day.. i also checked the reading at the CSV and AUX air.. i physically tested the CVS and AUX AIR valve.. they are working fine..

i can tell the car is running rich because it stinks like gas.. fuel consumption is terrible and the car wont hold an idle after the AUX air valve closes... too much fuel/ not enough air.. and when i drained the oil there was 10+quarts of liquid... mostly oil.. and about 2-3 quarts of gas from blow by.. its not coolant btw.. some guy asked how i know it was gas and not coolant.. well cause it wasnt milky looking... and i have good compression.. the oil was very thin and smelled like gas..

im starting to lean towards an ignition problem.. the car does have a misfire.. im not positive about the O2 sensor .. i checked it and it looks fairly new.. i think the PO had replaced it when he was trying to figure out why the car was running rich.. also installed a new Cat converter..i also unplugged the O2 to see if it made a difference.. and nope nothing...

im going to test the ignition components.. i have a ignition box off my parts car 1980 Euro 5spd Kjet.. will that work with the Ljet set up? ill find out soon i guess..

also fuel pressure test later today..

hacker-pschorr

What about the green wire?

When in doubt, replace it. If you have no idea the age and it doesn't look very new, just replace it.

Back to plugs, did you pull them to see if they all look even?