Starting Issue

[WNX700H]

My 88 Targa has started to become difficult to start when hot ..... cranks over fine but struggles to fire and then when it does, it is not running smoothly with constant idle until it seems to clear itself and then all is fine. Idle speed surges also during this . For the first time this morning it was also difficult to start cold with similar symptoms once it fired.

Most likely causes and solutions please

 

[les richards]

The DME relay is often the cause of most starting problems, they suffer from dry solder joints. Try another one as it's easy to swapl out. Worth carrying a spare, too.

 

[WNX700H]

Changed DME relay and then back again no change ....... car cranks over doesn't seem to fire at all then eventually begins to fire runs rough or cuts out but if you persist it eventually gets going and is then fine.

 

[chas3.2]

Hi. When were the TDC and speed sensors changed last
if never they only last 30 years.
Charles.

 

[T911UK]

As Charlie says, next after DME relay is the flywheel sensors.

 

[WNX700H]

If its one of the flywheel sensors then I don't understand how the car eventually starts and then runs fine?

 

[T911UK]

When they get hot they expand, probably go open circuit if damaged, when they cool down they work again

 

[WNX700H]

The problem I have is both hot and cold starting so temp affecting the sensors doesn't seem logical .

 

[chas3.2]

Have you looked inside the distributor cap + rotor arm.
Test fuel pressure could be fuel pump.
Old alarms do give trouble.

Charles

 

[WNX700H]

Ok so latest having unplugged temp sensor reconnected etc .... the car will start hot or cold but needs to be cranked much longer than it used to , it then begins to fire without throttle intervention ..... the car then does not seem to run on all cylinders but in say 10 sec it clears itself and then runs but with idle speed fluctuating for a further 30sec or so and then it runs ok. When the idle speed is unstable it will sometimes cut out but restarts easily and eventually runs ok .

Trying to avoid trial and error in changing bits out would rather diagnose cause and fix it if that is possible. DME has been proved to be not the issue having swapped it.

 

[chrishak]

One of the most common causes of fluctuating idle is the idle control valve, which may well contribute to the other symptoms (but don't quote me on that). OEM valves are not cheap so before buying a replacement, try removing it and cleaning it to see if that makes a difference.

 

[WNX700H]

OK this is driving me nuts ......
Changed DME relay ..... no effect
Changed cyl head temp sensor by just connecting new one when cold ...... no change. Reconnected old one no change.....

So now it starts cold and runs goes through warm up and idle adjusts itself ..... then if you just let the car run it will, every few minutes drop its idle speed almost to a stall then recover cycle like that twice and then be ok again.

Not taken it out on the road this is all sat idling in the garage , if you alter the throttle position it will also on times drop its idle sometimes to a stall.

 

[chas3.2]

Get the C/o mixture checked could be running to weak.

Any breather hoses split.

Inlet manifold gaskets blown out common fault.

Any vacuum hoses split. or fallen off.

Charles.

 

[WNX700H]

Ok been doing some further investigations,
- decided not to change any of the electronics until I was sure of any cause.
- On the basis that once it starts it ran and drove OK albeit with some idle issues I decided to look for vac leaks so stripped the inlets off and all breathers to do a detail inspection. The car is 30 years old but only covered 52k miles but still all the rubber bits are getting on. Changed the stepped pipe by the oil filter , both large breathers running across the back of the engine various other rubber bits , breather gasket at the back of the engine as I was in there anyway. Connection to the brake vac circuit looked suspect so renewed that. The car now runs much better and no erratic idle and now starts from cold without problems.
- The hot start issue remains though, if you leave the vehicle to stand, the engine will crank over merrily but it is reluctant to fire, eventually does fire but then cuts out , if you crank again it starts and then cuts out .... on the third or fourth attempt to start it, it then runs rough and then settles down and is fine.
- So my conclusion is its fuel pressure on the basis it starts cold ok so no fuel vaporisation issues but when hot the accumulator should retain the fuel under pressure and avoiding fuel vaporisation. So think either pressure regulator or pump is suspect although once running the car is fine so suspect pressure regulation is the more likely cause.
Anyone have any views on this?

 

[stuartbean]

I'll share my experience with failing Crank Shaft Sensors. First happened after a short journey, reversing into a space suddenly engine faded and stopped, would crank over but not start. After an hour I returned to car hoping it would start but it would only crank and not fire. Started fine when the recovery guy arrived! Happened again about a week later, and this time couldn't get it going again. Recovery guy suggested the crank shaft sensors after he did some electrical tracing to the "coil" (I don't really know much about motors yet, but the Porsche is making me learn quickly). Wouldn't start the next day but did start on the third day, and drove as far as the garage. Replaced both speed sensors (there are two if you are going to have a go). It's now been running perfectly well and starts hot and cold and I've done some distance to confirm.
The speed sensors were the Bosch ones, quite cheap (£70 each off ebay) - fitting charge reasonable as well. Apparently the sensors don't simply "fail" outright, but go on / off esp. with heat as they age.

What would be interesting to know is what happens when just one fails and the other is working - does the car simply stop or is one enough - does anyone know?

 

[WNX700H]

Hi

Does anyone have a known ‘good’ AFM for an 88 3.2 that I can either buy or borrow to either fix the running issues on my car or prove it’s the AFM causing the erratic idle , poor hot starting and running rich issues.
thanks
David

 

[chas3.2]

Hi David
I have a AFM you may borrow
But have you checked the inlet manifold gaskets to cyl heads.
Also the breather hoses oil tank to engine they split.
Distributer cap + rotor arm.
Have you had exhaust emissions test done.

Charles.

 

[WNX700H]

Hi Charles,

Thanks for your reply.

exhaust gas analysis shows co levels at 5 to 6% , would run lean if it had an air leak I think.

plugs are black and exhaust smells rich

inlet manifold gaskets have been renewed and breathers etc been renewed .

Whereabouts are you located ?


Best wishes
David
07394634782

 

[WNX700H]

Ok think I have now fathomed this with some help from IB community.
disconnected vac pipe to fuel regulator ....... started car and warmed up ,no pulsating idle every 45s.

so seems like the diaphragm in the pressure regulator / accumulator has broken allowing additional fuel to the motor via vac line. Fuel visible also from vac connection on regulator.

So so new unit to be ordered tomorrow which should prove the issue.