fueling issues [Archive] - SaabCentral Forums

: fueling issues


jasong
05-08-08, 11:12 AM
I have an 82 8valve giving me some fuel issues. The car is cis and evidently has low fuel pressure in the fuel head because the injectors are loading the cylinders up with fuel. I have replaced the suspect warm up regulator as well as every other test i can think of. Unfortunately I do not have the proper adapters to check head pressure. any possible problems anyone can come up with would be helpful. This car has been at the shop for about a year and they gave it to the saab guru to try and fix. Since I just started working for this company my rep is on the line.
;oops:

Jim Mesthene
05-08-08, 12:44 PM
I have an 82 8valve giving me some fuel issues. The car is cis and evidently has low fuel pressure in the fuel head because the injectors are loading the cylinders up with fuel. I have replaced the suspect warm up regulator as well as every other test i can think of. Unfortunately I do not have the proper adapters to check head pressure. any possible problems anyone can come up with would be helpful.
I can probably help, but you are at a severe disadvantage if you don't have the $1.50 adapters to properly test the system pressures.
I assume "head" means the Fuel Distributor. I assume "head pressure" refers to Line Pressure rather than Control Pressure.
This site has a good technical overview of Continuous Mechanical (CIS) Fuel Injection: http://www.diagnostic-assistance.co.uk/mech_inj.htm

First, disconnect the Cold Start Injector temporarily. Its (electrically controlled) behavior can confuse the diagnosis.
Second, check the intake manifold (look through one of the big Hose Grommets) to make sure there is no large puddle of fuel sitting in it.
Next, pull the 4 Injectors, jump the Fuel Pump, lift up the Air Flow Sensor Plate, and see if the Injectors leak, atomize and shut off.

Of course, you'll have to clean and dry the Plugs (use eye protection and blow out the cylinders too).

c900
06-08-08, 12:16 AM
I have an 82 8valve giving me some fuel issues. The car is cis and evidently has low fuel pressure in the fuel head because the injectors are loading the cylinders up with fuel. I have replaced the suspect warm up regulator as well as every other test i can think of. Unfortunately I do not have the proper adapters to check head pressure. any possible problems anyone can come up with would be helpful. This car has been at the shop for about a year and they gave it to the saab guru to try and fix. Since I just started working for this company my rep is on the line.
;oops:

Ok the most basic test is a fuel delivery rate test which doesn't need any special equipment and you should do that before worrying about measuring line pressure, residual pressure, etc. to check out what the warm-up regulator is doing.

What you need to do is remove the two large screws holding a pair of injectors into the intake manifold, very carefully extract them with the fuel lines attached (do it carefully since the lines can break), put the pair of injectors into a container like a metal mixing bowl or glass container and sit that somehow on top of the intake manifold, remove the 'snorkel' from the airflow sensor and fuel distributor assembly, manually operate the fuel pump by using a switched, fused jumper wire between sockets 30 and 87 of the fuel pump relay socket, and see how much fuel is expelled over 30 seconds when you pull up the airflow sensing plate (again do this carefully as it's a fairly precise mechanical device).

At the same time, you can watch the atomisation pattern out of each injector and make sure it's a good atomised spray which looks even.

The Bentley manual specifies about how much fuel should be expelled over the time period (I'm sure it's 30 seconds but it's been a while since I did that sort of test on one of my 8v cars), and if you get the right amount or better, the fuel pump, fuel pump pickup/filter, and the fuel filter (in the engine bay for an 8v car) are all good.

What you say about the injectors 'loading up' the cylinders with fuel would not be a low fuel pressure problem as K-Jet injectors inject fuel continuosly once the pressure is over a certain level, and don't stop until the pressure (regulated by the fuel distributor) falls. If the line pressure is down, but it's high enough for the injectors to still open, and the pressure differentials through the warm-up regulator, etc. are stable, you'll most likely get less fuel into the intake passages for a specific distance that the airflow metering plate is raised, assuming the pressure regulating valve (which sets the basic line pressure) on the side of the fuel distributor unit is ok.

What it could be is leaking injectors - over time the injectors don't seal as well when 'closed' and they can still leak fuel into the intake manifold passages. That would artifically change the fuel/air mix to make it richer which would be particularly problematic when starting the engine if it's too rich. This is one thing which the cold-start injector wouldn't help with as it's designed to make the fuel/air mix richer when starting, but if it's already enriched from injector leaks, starting could be delayed while the fuel/air mix re-stabilises as air is drawn through.

Craig.