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Issues with fuel injectors and chasing warm start problems
I have been chasing a problem on a 993TT that has been a real pain to solve. Here is a short version of the situation:
On my 97 993TT, I pulled out the injectors and had them cleaned -> no issues, and they seem to work fine (2500 miles on them now).
Did a service on a 96 993TT - replaced the plugs and had the injectors cleaned at the same place since it worked fine for my car
The 96 is modified, with an adjustable fuel regulator, K24's and chipped
The 96 seemed to run strong, but started to be hard to start when warm - usually 2 hrs+ after stopping. At times it would take up to 30 seconds of cranking with zero ignition, then it would start roughly and finally start to run smoothly. Sounds totally like lack of fuel or flooding.
DME relay swap with two other relays makes zero difference.
Cold and hot starts seem to be fine, with a bit of minor hesitation
The 96's fuel consumption appeared to have increased
Ok, for diagnostics :
Checked fuel pressure, the car is running around 70psi (5 bar) which is about right with the mods
Fuel pressure retention is within spec
DME relay swap makes no difference
Vacuum is good
Heat temp sensor is working properly (reading via a Hammer)
Pulled a spark plug - appears to have a light dark carbonization which indicates a rich mixture
So I then swapped the fuel injectors in my car with this car, and interestingly enough, the problem follows the fuel injectors. My car then became hard to start when warm, and the 96 started fine with my injectors. So the problem appears to follow the injectors.
So we took the injectors back to the cleaners - and they retested flow and spray, they claim they are identical and they changed nothing that should cause this. That was our second revisit since we took them back when the 96 became hard to start. They then threw their hands up and said it's not their problem and it's the cars fault !!- but clearly something changed with the injectors since the problem follows the "bad" set, so they are bull of BS.
We are now taking the injectors to another company for testing since we have lost all faith in the first company. I will post their name an give a bad review at all the social media sites if it turns out it's their screw-up. A couple of observations :
The cleaners test notes show less flow in the bad injectors AFTER cleaning, which is totally counterintuitive.
The cleaners invoice show different filter baskets part numbers for the same injectors, which the rebuilders claim is not an issue. Really??
How can it not be the injectors themselves?
If you guys have any other (good) ideas would appreciate it.
Looking forward to how this sorts out. All this work, would it be cheaper to just buy new injectors?
Sunset price is $327 each - ouch. We will be looking for other sources.
We just got back some results from the second company, they say the injector spray patterns go random when they are hot. So WTF did the first company do to the injectors to screw them up that badly, given they were working fine when I pulled them out. They test fine cold.
Nope. Its not the pintle caps anyways, they are only to protect the needle valve and hold the O ring in place.
I need too see the test results again, but I think the technician ( I hesitate to call him that because his hand writing is like a 2 year old, prob did not have hair when these cars were made) ran the injectors at a high frequency - he might of cooked them. The trick is all of them are screwed, not just one, so it must of been something the first company did. Very hard to prove though.
** update: the tech ran them at "10,000 RPM, duty cycle 25%". See pict below, funny how the flow rate is lower after cleaning: BTW, my injectors were tested at 5000 RPM.
Mike, if possible use RC injection (SoCal) in the future.
Injectors can be cooked by leaving them on the machine too long. There is a fair amount of info out there about it.
SCARGO does a LOT of upgrades to 60lb injectors. One option is to buy a used set from them and send to RC Injection. The other is to convert the 5 Bar stock injectors to 60lb Seimens with 4.2Bar FPR. Protomotive has a GREAT tune for that. They are a better injector in every way.
Well my 96 was the unfortunate in this situation. For any locals or those on West Coast, you need to stay far away from:
NW Fuel Injection Service in Surrey
In addition to damaging them and poor diagnostic skills to confirm it, it took one visit to another local shop Fred Holmes Fuel Injection to confirm all 6 injectors are toast and not rebuildable. NW basically sends you out the door offering no form of acceptable customer service for their error.
Anyways I'm now on the hunt for new Bosch injectors. It seems like the best avenue to take right now.
For future RL reading, proceed with caution when sourcing out a place to service injectors.
Obviously they can fail outright, but this particular set tests fine when cold, but if you heat them up (like on a warm 911) they start to be unpredictable, with varying volume, etc. Static tests, like holding pressure works fine as well.
The solenoid inside the injector is not designed to be on all the time (100% duty cycle), so if the tech for instance turned them on solid or push the harder than specified they will overheat and trigger failures.
What I have not been able to find is the impact of running these specific injectors at a high frequency as they did (10,0000 rpm, or 5,000 activations./minute, so that is a frequency of ~83 Hz). That is well beyond what these have ever been run at, could that also cause issues? The test notes above are a bit cryptic, but at that speed, you only have 1.2ms for each cycle. He wrote M.S. 3.00 -> if that is the time the injector is on each cycle, basically he forced the duty cycle to 100%.
What happens to fuel injectors that they become roasted and unuseable? How does this happen?
Fuel injectors are a simple solenoid. When "pulsed" they open.
When cleaning injectors you can run them at maximum pulse rates for long periods of time. The injectors were not designed to handle this and over heat. That damages the internals.
Most modern injector cleaning machines have dummy proof setting to prevent this. Higher pulse width automatically lowers RPM simulation to prevent this sort of thing.
Anyways I'm now on the hunt for new Bosch injectors. It seems like the best avenue to take right now.
Don't shy away from some good used ones. They are not really a consumable item. Check with Protomotive or SCARGO. I bet they both have a fair amount of good used ones. Then send em to to RC Injection for profession cleaning and servicing.
Fuel injectors are a simple solenoid. When "pulsed" they open.
When cleaning injectors you can run them at maximum pulse rates for long periods of time. The injectors were not designed to handle this and over heat. That damages the internals.
Most modern injector cleaning machines have dummy proof setting to prevent this. Higher pulse width automatically lowers RPM simulation to prevent this sort of thing.
07-18-2017, 03:29 PM
Issues with fuel injectors and chasing warm start problems
