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Guys, but this is not a real injector, this is the metal pipe in which the fuel is pumped by the injection pump. What can break in such a metal tube?
It's job is to atomize the fuel so it's just not a pipe.
It has a pintle and return spring. It is opened by fuel pressure; hence the "continuous" in CIS.
As for the old injectors, the pintle spring weakens and could allow the injector to leak of not close properly. Clean them all you want but you can't fix that.
100% buy new ones.
rockauto dot com has the OEM Bosch units for sale at the best price I could find.
I had mine professionally serviced and the results were disappointing and wasted time, caused a hot-hard start symptom.
don’t crack your injector bodies when tightening.
replace your fuel filter while your back there.
also, check all
your intake manifold studs. Including the inaccessible cylinder 3 inboard nut. It requires you to lift the CIS head and gently move it 2-3 inches to the right. Which is not so difficult when the injectors are disconnected.
this is what I found when I did…. I’ve owned the car for 12 years, and it has one previous owner. Maybe the porsche tech went for lunch and forgot to put it back on after?
also, buy a cheap borescope of Amazon from depstech. You can see down your injectors bores and inspect the intake valves.
@fritz k. Nice work, thank you for sharing the informative pictures!
At some point...the plastic intake manifold flanges need to be inspected and replaced.
I recently split the case on my low mileage '94 and 3 of the 6 plastic housings had hairline cracks.
@fritz k. Nice work, thank you for sharing the informative pictures!
At some point...the plastic intake manifold flanges need to be inspected and replaced.
I recently split the case on my low mileage '94 and 3 of the 6 plastic housings had hairline cracks.
+1
Back in 2013 I had a rich issue on boost and an inability to adjust the engine idle speed. These symptoms were directly attributable to a cracked injector block, which I addressed during an engine reseal/SC cam installation in 2014. I took the liberty of port matching the intake and the blocks because who leaves 2-3 hp on the table
Everyone's injector blocks are 30 years old if they haven't replaced them yet and they WILL be a source of trouble eventually.
Last edited by Metal Guru; 12-01-2022 at 05:54 PM.
yep, I just replaced all my injector blocks last winter. Owned the car for 19 yrs now, and was having a surging idle problem. 3 out of the 6 were cracked to varying degrees
@Nyx Curious what was the "hot start symptom"?
thanks
Once the car had come up to operating temperature then shut off for about 45+ minutes it would be a long crank to start again. The symptom only appeared once they were cleaned. My guess is any deposits on the seat of the valve were washed away. These deposits would’ve allowed the valve to have sealed prior to the cleaning is my guess.
Always interesting stuff on this thread - I have "hot start symptom" on my 73, despite new injectors, refreshed MFI pump, etc., 66,000 orig miles, don't think the throttle bodies are toast yet.
Always interesting stuff on this thread - I have "hot start symptom" on my 73, despite new injectors, refreshed MFI pump, etc., 66,000 orig miles, don't think the throttle bodies are toast yet.
Under the condition of new and non leaking injectors the pressure accumulator is at the top of the list of suspects. Can be checked by measuring the control pressure at the warm-up regulator. After switching off the fuel pumps, the pressure drops to approx. 2 bar, within 20 minutes it must not drop below 1 bar.
If this is o.k., there is still the possibility of false air or a malfunction of the thermo time switch that controls the cold start valve.
"Hot Start" issues were called Vapor Lock in the days of carburetors.
If the fuel line has no or low fuel pressure, heat soaking after shutdown creates fuel vapor which will interrupt fuel flow. Once the vapor is vented and fuel flows, the car starts.
Old car with mechanical g-rotor fuel pumps were susceptible to vapor lock due to low fuel operating pressure and the fact that the fuel pump was usually above the height of the the fuel tank.
The solution to this is to hold fuel in the system under high pressure, which prevents fuel from vaporizing. If either end of the fuel system is not holding pressure, then long crank times will occur. On a CIS fuel injection system, either the fuel accumulator or the fuel injectors themselves can be the culprit.
Ian, did your shop test the new injectors before they blamed them for the problem? I'd never clean the old injectors and reuse them. They never get completely clean and the pintle springs are fatigued. Ordinarily, replacing your injectors shouldn't result in any issues if the engine was re-assembled properly.
I deferred to my shop (they are very good IMO and have a great reputation locally) who pulled my injectors and instead of replacing them with the new ones I purchased; they tested, cleaned and reused the old ones. They said they were fine. With that said my hot start problem has persisted (although not as bad - maybe b/c of a new accumulator) and the last time I was in the shop owner said "maybe we should replace the injectors"..... so that's where I am at. New injectors are on the list as is replacing the oil lines (not leaking) @ some point over the "winter". I did replace the injector blocks.
It does sound like Bosch injectors are fine vs Porsche (since maybe they are one in the same??).
11-27-2022, 02:33 PM
