Narrowing down my start issue (84 4kq) [with suggested procedure]

[John Cody Forbes]

I have two five gallon buckets filled to the brim with bad warm up regs diagnosed with a simple fuel pressure test that takes 5 minutes. Changing parts on hunches and well meant educated guesses may work for those with parts cars or a fleet of similar cars, but in the professional world my customers don't want to hear "yeah I changed the temp sensor, see if that works". There is a test procedure for everything that can lead to fixing problems by only changing the things that are actually broken 90% of the time. I understand that not everybody has all of the equipment that a shop does, but in this case a fuel pressure gauge set is very inexpensive (cant they be had at Harbor Freight for like $40?) and would take a minute or two to install and KNOW what is going on with the fuel pump, injectors, DPR, and others. CIS is not like a carb or EFI system where the system pressure is important, but can be 10% off before it's noticeable to the driver. The system pressure on CIS is not even very important, but the control pressure that controls the movement of the metering plate is *critical*.

Now with that all said, is it possible this problem is ignition related? OP mentioned that the PO changed many things in the fuel system and had it looked at many times. Could it possibly be that he was barking up the wrong tree? IIRC the car in question has a basic ignition system (vacuum advance distributor, no ECU), right? It's sort of unlikely, but maybe the advance is sticking all the way retarded for a time?


Also, a smoke test would be pretty useful just to be certain of the vacuum system. I've made a "smoke machine" before out of a quart paint can with the lid soldered shut, some WD-40 or ATF as smoke fluid, two pipes soldered to the sides to let air in and smoke out, a propane torch to make the smoke, and an electric tire pump to do the air moving. Sounds silly, but I discovered and fixed a few small leaks on a car that way. 

-Cody (mobile)

On Aug 16, 2010, at 2:35 AM, Huw Powell <audi at humanspeakers.com> wrote:

> 
>> Now that you have gotten to the point of things that Cody and Huw,
>> and others are pointing out, they may want to suggest clever ways to
>> do these tests.  Although I have done most of these in my ownership
>> of CIS cars, in most cases I never needed to go to the point of fuel
>> pressure tests  since I usually got things sorted by then.
> 
> I have never - NEVER - seen any need for fuel pressure tests.
> 
> Vacuum leaks and the resulting maladjusted static fuel mixtures, 
> endlessly.  On almost every CIS engine I have encountered.
> 
> -- 
> Huw Powell
> 
> http://www.humanspeakers.com/audi
> 
> http://www.humanthoughts.org/
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