dogleg

hi

i have just bought a 1981 924 2.0 litre non turbo cis injection.the car has a bad running issue.it runs perfectly at idle speed and it can be revved on and off cleanly.but it wont hold a steady throttle.if i try to hold the throttle at 2k rpm it just runs super rich putting black smoke out the exhaust.
any advice on where my fault is?i suspect injectors or maybe wur.

mel_t_vin

Does your car run rich when cold, when hot, or all the time?

CIS injectors are very simple...I doubt they are your issue.

In order for a CIS-injected car to run properly, there are a couple things to check...CO% present in the exhaust [measured at factory specified RPM] and WUR cold/warm control pressures. This will require the use of an exhaust gas analyzer [AKA tailpipe probe] and a set of CIS pressure gauges. If I had access to a WSM, I would provide you the factory specifications.

While the CIS gauges only cost about US$100, the EGA is probably cost prohibitive. Are there any decent independent Euro shops in your area?

morghen

Injectors are probably not the fault. They are just a pipe with a spring and ball/cone.
Wur does not enrich based on vaccum or boost, as this is a NA.

Check for vaccum leaks, the air tract from the CIS to the TB and further to the cyl head must be leak free. Probably someone adjusted the mixture to compensate for the vacum leak?

dogleg

thanks for the replies

the car starts normally for cold,seems about right on mixture at that stage.but as it heats up in runs richer and richer,car has no vac leaks.i have adjusted the co adjustment by ear to have the car running about right when hot.at this point the engine can be revved quickly on and off perfectly.but if i try to hold a steady throttle it just smoothers its self after a few seconds.
ive been doing some reading on the cis system and agreed the injectors are simple and unlikely to be giving this fault.my plan of action tomorrow is to jumper the fuel pump relay and see if im getting the 750ml of fuel in 30 seconds the system needs to operate.also i think theres an ohm test that can be carried out on the WUR.
i think ill have to buy a set of the fuel gauges.there is a specialist near but id like to sort this fault myself and keep the costs down.

any more thoughts gladly welcomed!

dogleg

update for anyone interested.
took an ohm reading cold across the two pins on the WUR and got a reading of 18.4 on the 200 setting
disconnected the fuel feed pipe between the filter and the metering unit removed the fuel relay and jumpered the two connecting to run the pump constantly and got a delivery of fuel of 1,800 ml or cc after running the pump for 30 seconds.
reconnected fuel lines removed one injector jumped the pump again and manually lifted the plate sensor and got what i think is a bad spray pattern of fuel not cone shaped just a straight line of fuel uneven in its delivery which i think may mean the injectors are bad.
am i on the right course of action here to solve this problem?

morghen

Injectors should spray in a cone shape not **** in a straight line, check the fuel pressures before doing anything else. Search how to test fuel pressures for the 924, get the right gear and do the test.

I had a similar issue 12 years ago, i replaced the injectors and the car didnt start anymore. The fuel pump was weak and could not even open the injectors. Further, the fuel pump electrical circuit was old and weak and could not properly feed the pump the current it needed to create the right pressures.

dogleg

thanks morghan

yes thats exactly what its doing pissing in a straight line.your right next step is the gauges on and see what pressure i have.ive ordered a set of injectors as there only $35 each and the gauge kit.have to wait a week or so for them to arrive though.
fingers crossed!