928 starts and runs good, then after a bit dies and won't do more than idle

[challengergary]

My 17 year old son got a 1979 928 as a Christmas gift form one of my best friends who had it for about 4 years and did nothing with it.

We have since got it running and he has really been enjoying it but lately we have been having what seems like fuel issues. It starts and runs perfect but after driving it for a while, it seems to starve for fuel and will not do much more than idle. If you give it gas, it misses and pops and farts.

We replaced the external fuel pump but it still does the same thing. It runs great up until the time when all of a sudden it doesn't. HELP!!!

[JK McDonald]

Hey Challenger - I guess you've replaced the fuel filters (internal and external of the fuel tank ? Have you worked on the Bosch CIS fuel injection system before? It is not difficult to troubleshoot but to determine if you have a fuel pressure (supply or control) issue you will need the CIS pressure test gauge and hoses. There are set pressures that must be met to determine the air/fuel mixture which controls how the motor runs when transitioning from cold to warm. This control pressure is regulated by the "Warm-Up Regulator".

Where are you located ? Perhaps there is someone near by that can help you sort this out ?

Michael

[stepson]

Challenger,
Absolutely is necessary to have the pressure gauges to adjust CIS 928 engine as pointed out by Michael in post 2

In addition, where did you source the fuel pump with which you replaced the original? CIS systems run at greatly increased pressures from EFI cars. A fuel pump with insufficient pressure may allow the engine to start and idle, but will run out of fuel much above idle. Make very sure that the fuel pump is correct for your model 928.

[challengergary]

We only replaced the external pump. I will pull the one in the tank and see if the strainer is clogged. Never worked on one of these systems before so it is all Greek to me...