Fuel Pressure
Thread Starter
Burning Brakes
Joined: Nov 2007
Posts: 1,213
Likes: 2
From: Cincinnati oh
Fuel Pressure
I have a 1985 I have new Bosh 3 injectors newer fuel pump, new fuel sending unit replaced the fuel filter last year.
It was running fine. a few days ago I had a fuel gauge issue where the float was hung up @ 1/4 tank. I pulled the fuel sending unit re adjusted it and it was fine.
Today it stalled a couple times when it was @ idle making a turn and seemed to stumble a few times under acceleration. I checked the Fuel pressure @ the rail and it goes to 40 and drops quickly to 0 with the battery on.
When it starts it idles @ 38-40 but drops to around 30 when i accelerate the engine.
Please ideas are needed.
It was running fine. a few days ago I had a fuel gauge issue where the float was hung up @ 1/4 tank. I pulled the fuel sending unit re adjusted it and it was fine.
Today it stalled a couple times when it was @ idle making a turn and seemed to stumble a few times under acceleration. I checked the Fuel pressure @ the rail and it goes to 40 and drops quickly to 0 with the battery on.
When it starts it idles @ 38-40 but drops to around 30 when i accelerate the engine.
Please ideas are needed.
Thread Starter
Burning Brakes
Joined: Nov 2007
Posts: 1,213
Likes: 2
From: Cincinnati oh
Fuel presure regulator is about 3 years old. I should also mention i kinda smell gas, and it has a new EGR valve and cyilnoid.
I did not disconnect the Fuel pressure regualtor with the vaccum line what will that do?
I did not disconnect the Fuel pressure regualtor with the vaccum line what will that do?
Safety Car
Joined: Aug 2009
Posts: 3,751
Likes: 276
From: Melbourne, Victoria, Australia
I have a 1985 I have new Bosh 3 injectors newer fuel pump, new fuel sending unit replaced the fuel filter last year.
It was running fine. a few days ago I had a fuel gauge issue where the float was hung up @ 1/4 tank. I pulled the fuel sending unit re adjusted it and it was fine.
Today it stalled a couple times when it was @ idle making a turn and seemed to stumble a few times under acceleration. I checked the Fuel pressure @ the rail and it goes to 40 and drops quickly to 0 with the battery on.
When it starts it idles @ 38-40 but drops to around 30 when i accelerate the engine.
Please ideas are needed.
It was running fine. a few days ago I had a fuel gauge issue where the float was hung up @ 1/4 tank. I pulled the fuel sending unit re adjusted it and it was fine.
Today it stalled a couple times when it was @ idle making a turn and seemed to stumble a few times under acceleration. I checked the Fuel pressure @ the rail and it goes to 40 and drops quickly to 0 with the battery on.
When it starts it idles @ 38-40 but drops to around 30 when i accelerate the engine.
Please ideas are needed.
The 85 has 24lb injectors standard so have a lower fuel pressure, my 85 was 30-32 psi but some forum members have said they have around 38-40 psi.. TPI's love more fuel 45 psi is a sweet spot but can make idle rich and fail emissions testing however improved mid range and top end performance.
Do you have a standard fuel pressure regulator or is it and adjustable type (with screw for adjustment on top)
I never noticed any stumbling under acceleration at 30 psi with the TPI in standard form, she always accelerated hard breaking traction as the rpm and torque rise.
You may need to check for fouled plugs or bad ignition leads, if the idle screw has been tampered with you may need to set the base idle again.
Check your TPS throttle position sensor (top and middle wires with multimeter and set 0.54 volts at idle or ignition on and check it rises steadilly to 4.5 volts full throttle (no need to run engine ignition on is all that is needed)
Reset the ecm there is a cable near the battery to reset codes as the ecm will try to counteract things and get in a knot.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Sometimes the fuel pressure regulator diaphragm ruptures or develops a hole. If that happens the vacuum line will fill up with fuel and it will end up in the plenum. Usually when that happens the engine will run rich because of the extra fuel. In extreme cases you'll get a fire (happened to me -- you can see where the fuel pressure blew the vacuum line off the FPR. Fuel sprayed all over the engine. The white powder is from the fire extinguisher. When I took off the plenum fuel poured out of it.):
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
If you take off the hose and you smell gas, you have a problem with the regulator diaphragm being torn or leaking.
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
The vacuum controls the fuel pressure. When you go to WOT the vacuum drops to almost zero, which raises the fuel pressure. The vacuum at idle is very high, which gives you minimum fuel pressure.
Sometimes the fuel pressure regulator diaphragm ruptures or develops a hole. If that happens the vacuum line will fill up with fuel and it will end up in the plenum. Usually when that happens the engine will run rich because of the extra fuel. In extreme cases you'll get a fire (happened to me -- you can see where the fuel pressure blew the vacuum line off the FPR. Fuel sprayed all over the engine. The white powder is from the fire extinguisher. When I took off the plenum fuel poured out of it.):
Sometimes the fuel pressure regulator diaphragm ruptures or develops a hole. If that happens the vacuum line will fill up with fuel and it will end up in the plenum. Usually when that happens the engine will run rich because of the extra fuel. In extreme cases you'll get a fire (happened to me -- you can see where the fuel pressure blew the vacuum line off the FPR. Fuel sprayed all over the engine. The white powder is from the fire extinguisher. When I took off the plenum fuel poured out of it.):
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Le Mans Master
Joined: Feb 2005
Posts: 6,479
Likes: 565
From: Clearwater Florida
..... You have to keep over 1/2 tank of fuel in just about any C4 for adequate fuel supply to the pump during maneuvers and brisk acceleration ... otherwise the fuel sloshes , the pump sucks air and the engine stumbles ........................
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
Haven't seen that in the few cars on the auto cross runs. They run with a quarter tank for weight savings. Have to try it out myself since I always run till empty before filling up.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I have only had that happen ONCE since I got my car in 1985. I was on a freeway cloverleaf and going pretty fast and it stumbled. I autocrossed this car from 1986 until 2002 and never had that happen.
Safety Car
Joined: Nov 2009
Posts: 3,973
Likes: 341
From: Adelaide South Australia
Ive got exactly the same issue as you shamdave, I know its a leaking injector in mine coz the reg diaphragm and fuel pump are new,
there are 3 major things that will cause the fast pressure leakdown, the pump not holding pressure, the diaphragm not holding pressure or the injectors not holding pressure,
one trick i tried was to undo the out fuel line at the tank and got my brother to put pressure into the fuel system with a compressed air gun while i listened at the engine,
well it worked, i could hear the injector leaking, until he squeezed a fraction too hard and it went to 65 psi, then the leak stopped ! seems that putting in more than 44 psi that the reg was set at closed up the leaking injector/s.
unfortunately it didnt fix the problem coz when i started it and ran it, stopped the engine, the fuel pressure dropped of quickly again, so it looks like the leaking injector/s pintle valve has jammed open again when it started operating.
anyway have ordered a new set of bosch 3 30lb injectors from Jon today (its only money !)
there are 3 major things that will cause the fast pressure leakdown, the pump not holding pressure, the diaphragm not holding pressure or the injectors not holding pressure,
one trick i tried was to undo the out fuel line at the tank and got my brother to put pressure into the fuel system with a compressed air gun while i listened at the engine,
well it worked, i could hear the injector leaking, until he squeezed a fraction too hard and it went to 65 psi, then the leak stopped ! seems that putting in more than 44 psi that the reg was set at closed up the leaking injector/s.
unfortunately it didnt fix the problem coz when i started it and ran it, stopped the engine, the fuel pressure dropped of quickly again, so it looks like the leaking injector/s pintle valve has jammed open again when it started operating.
anyway have ordered a new set of bosch 3 30lb injectors from Jon today (its only money !)
Pro
Joined: Sep 2012
Posts: 610
Likes: 12
From: Seattle Wa
New doesn't always mean good. In 45yrs of working on cars, I've gotten lots of bad parts right out of the box, and its not uncommon for fuel related parts to fail early if the aren't properly assembled. h
Thread Starter
Burning Brakes
Joined: Nov 2007
Posts: 1,213
Likes: 2
From: Cincinnati oh
Ok so I checked the Fuel pressure regulator.
It runs about 46-48 with out the vacuum line and i do not smell gas, so im lead back to the fuel sending unit and pump.
Also it seems to stall more when its cold
It runs about 46-48 with out the vacuum line and i do not smell gas, so im lead back to the fuel sending unit and pump.
Also it seems to stall more when its cold
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
Does it hold pressure after shutdown? For how long? What is the drop off like? Check it after 1 hour and 2 hours.
Thread Starter
Burning Brakes
Joined: Nov 2007
Posts: 1,213
Likes: 2
From: Cincinnati oh
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
Without the 9th injector, you will need ECM changes to enrich the fuel spray if I am reading those that have done it correctly, Also it could be the fuel pressure drop.
Team Owner
Joined: Jan 2003
Posts: 20,306
Likes: 242
From: Summerland B.C. Canada
Also,there is a pulsator between pump and supply line in tank. That can also leak and cause a quick loss in pressure.
Thread Starter
Burning Brakes
Joined: Nov 2007
Posts: 1,213
Likes: 2
From: Cincinnati oh
Also,there is a pulsator between pump and supply line in tank. That can also leak and cause a quick loss in pressure.[/QUOTE]
I eliminated that and replaced it with a hose and clamps
which one is the return line? Looking at the FSU standing at the back of the car of the 2 lines on the right the top or bottom?
I eliminated that and replaced it with a hose and clamps
which one is the return line? Looking at the FSU standing at the back of the car of the 2 lines on the right the top or bottom?