Testing/Adjusting Fuel Pressures and a rough cold idle

[mark w]

I tested my primary/system and control fuel system pressures.

I am trying to see if a part is faulty that may be causing a rough, cold idle.

As the car warms, at idle, it smooths out. this takes only a few mnutes. Also at the same time, the Lambda system becomes active as can hear and monitor the frequency valve start to function with the dwell meter. I have no hot/cold starting issues or driveability issues hot or cold. Only a rough, cold idle. I have the UK exhaust and correctly set air/fuel mixture. I do not have engine loping and I have the DMCH fuel pump. the car starts quickly and cold start system is functioning, this is not a starting issue.

I first thought maybe the heater circuit in the control pressure regulator (CPR/WUR) was not functioning. i tested for this and it is ok, I can see the Control pressure rise (leaning the mixture) as the coil heats the unit from 55 deg F. i also tested my vacuum acceleration enrichment function and that works. I also tested that the vacuum valve (Green one on the Y-pipe) was connected right and working/routing vacuum to the WUR at the 55 deg temp.

on the idle circuit, tested its coolant temperature sensor (two wire plug on the y pipe) and it also was giving values in range when measured at the idle ecu connectors.

my fuel pressures tested at 63 psi system and 22 psi control (at 55 deg). this is too low.

i then removed my primary pressure regulator from the Fuel distributor, and i added another shim that had from another distributor. this raised my pressures to 70 psi and much closer to spec. I ran the car then for a while and as it heated up it was still a but rough. i plugged in the wire for the heater on the WUR control pressure came up to about 55 psi. again now in spec.

tomorrow I will see what it does again from cold and no residual pressure and let t heat up fully and then reset mixture.

Looking for comments with regards to what Ive done- is it all right- and what may of caused the low pressure- and looking for ideas. Thanks.

Mark W

[David T]

Everything you did so far was correct. Rough running till it gets into closed loop is normal to a point. Watch the pressure on the control valve as it warms up and follow the chart, the pressure should rise close to the values given. Not unusual for it to be off a bit, the more it is off the rougher it will run. The CPR can be re calibrated to run smoother if necessary. The Delorean vendors can help you out or you can try to do it yourself.

[dmcman73]

I tested my primary/system and control fuel system pressures.

I am trying to see if a part is faulty that may be causing a rough, cold idle.

As the car warms, at idle, it smooths out. this takes only a few mnutes. Also at the same time, the Lambda system becomes active as can hear and monitor the frequency valve start to function with the dwell meter. I have no hot/cold starting issues or driveability issues hot or cold. Only a rough, cold idle. I have the UK exhaust and correctly set air/fuel mixture. I do not have engine loping and I have the DMCH fuel pump. the car starts quickly and cold start system is functioning, this is not a starting issue.

I first thought maybe the heater circuit in the control pressure regulator (CPR/WUR) was not functioning. i tested for this and it is ok, I can see the Control pressure rise (leaning the mixture) as the coil heats the unit from 55 deg F. i also tested my vacuum acceleration enrichment function and that works. I also tested that the vacuum valve (Green one on the Y-pipe) was connected right and working/routing vacuum to the WUR at the 55 deg temp.

on the idle circuit, tested its coolant temperature sensor (two wire plug on the y pipe) and it also was giving values in range when measured at the idle ecu connectors.

my fuel pressures tested at 63 psi system and 22 psi control (at 55 deg). this is too low.

i then removed my primary pressure regulator from the Fuel distributor, and i added another shim that had from another distributor. this raised my pressures to 70 psi and much closer to spec. I ran the car then for a while and as it heated up it was still a but rough. i plugged in the wire for the heater on the WUR control pressure came up to about 55 psi. again now in spec.

tomorrow I will see what it does again from cold and no residual pressure and let t heat up fully and then reset mixture.

Looking for comments with regards to what Ive done- is it all right- and what may of caused the low pressure- and looking for ideas. Thanks.

Mark W

Pull all the injectors and place each one in a jar. Jump your fuel pump to stay on and then check the injectors. Without touching anything, there should be no leaks or drips. Press the metering flap down and verify all injectors have a uniform spray pattern and they are outputting the same volume (measure the contents of each jar).

Rough running could be from a bad injector or even a bad spark. You might even want to do a compression test on each cylinder if everything else checks out.

Did you check your timing as well?

[mark w]

Pull all the injectors and place each one in a jar. Jump your fuel pump to stay on and then check the injectors. Without touching anything, there should be no leaks or drips. Press the metering flap down and verify all injectors have a uniform spray pattern and they are outputting the same volume (measure the contents of each jar).

Rough running could be from a bad injector or even a bad spark. You might even want to do a compression test on each cylinder if everything else checks out.

Did you check your timing as well?

ignition timing is verified- 13 deg.

yes that was a next step- to pull the injectors. i just did that on another car and still have the bottles. thanks for the recommended next step.

ive not yet checked compression

thanks for the replies.