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Bosch Injectors #1634126
22/07/2019 13:40
22/07/2019 13:40
Joined: Feb 2019
Posts: 56
Behind a blue gate
clanger Offline OP
Reaping the fruits
clanger  Offline OP
Reaping the fruits

Joined: Feb 2019
Posts: 56
Behind a blue gate
I know the standard Bosch 0280150450 20vT injectors were discontinued in 2008. My question is has anybody found a replacement? I've seen reference to Lucas Denso and they seem to produce a 360 cc injector but the impedance is 12 rather than 16 Ohms and I suspect this would cause a problem.

My current injectors are visibly dripping; fuel rail drops from 3 bar to 2 bar in 10 mins. After half an hour all pressure lost. This is causing hard starting from flooding (I can smell fuel on the engine oil) and I can hear vapour being pushed back in to a full tank of fuel if I cycle the ignition key several times before trying to start. I've changes the O rings, filter baskets etc. and they have a good uniform spray pattern but warm start is just a pain.

Really don't want to buy second hand from ebay as they could equally be shot and don't trust units from the far east.

Any advice?

Re: Bosch Injectors [Re: clanger] #1634128
22/07/2019 14:54
22/07/2019 14:54
Joined: Dec 2005
Posts: 3,657
Pothole City
GrahamL Offline
Forum is my job
GrahamL  Offline
Forum is my job

Joined: Dec 2005
Posts: 3,657
Pothole City
You could try having them cleaned, eg. https://www.asnu.com/service-centres

or buy a cheap ultrasonic cleaner from ebay and DIY.

Re: Bosch Injectors [Re: clanger] #1634134
22/07/2019 18:41
22/07/2019 18:41
Joined: Dec 2005
Posts: 32,217
Hemel in the Hempstead
barnacle Offline
Club Member 18 - ex-Minister without Portfolio
barnacle  Offline
Club Member 18 - ex-Minister without Portfolio
Forum Demigod

Joined: Dec 2005
Posts: 32,217
Hemel in the Hempstead
I discussed this very subject with Joe only the other day (though I don't recall which injectors he was asking about, the impedances were very similar). He had come across a car with 12 ohm impedance which had been running for some time without issue.

Here's the (electronics engineer hat on) deal.

1) current through a circuit is proportional to the loop resistance of the circuit - in this case, the current therefore would increase by about 33%.
2) power dissipated in a circuit is equal to the voltage across that circuit multiplied by the current - so the power dissipated by each injector will be around 16W, most of which is absorbed through the manifold and the fuel flowing through the injector. We can assume that Lucas are happy with that sort of load.
3) the injectors are switched on using a transistor in series with the injector coil. That transistor - one per injector - is in the ECU housing. The transistor is always either off (and dissipating no power) or hard on, with a voltage drop of about 0.2v (guessing here from 1990's power transistor spec; I don't know which transistor is actually used) and so when it's turned on, the power dissipated by the transistor's internal resistance will be around 200mW; no great problem as it's bolted on to a heat sink on the case of the ALU.
4) the bad news: between those two extremes, the transistor is either switching on or off, and it can't do that instantaneously. The time it takes to do that depends on the transistor characteristics (which I don't know), the circuit configuration (which I don't know) and the speed the engine is running. While it's switching, it's not a switch, it's another resistor in the circuit and it's dissipating like mad. As the engine runs faster, the proportion of the time that it spends in this switching time vs either on or off increases, so the worst time is when you're running maximum revs - where each transistor would be dissipating around 33% more than the ECU was designed to...

Ok, we do have a couple of points: first that Joe knows of at least one case where they have been successfully run for some time (I don't know how long). Secondly, no designer worth his salt would use transistors running particularly close to their limits, particularly where the environment in which they would operate is so harsh, and where they're expected to work for decades. Personally, I'd spec at least two hundred percent overload, and try and get five hundred past the production engineers (they're more expensive!).

So, my *BEST GUESS*, no guarantees, is that at normal speeds there will be no issues. I'd check the ECU after a fast run with the correct injectors and see if it got too hot to touch; if it does, I would be very wary of changing to those lower impedance injectors. If it feels ok, change them and then do the same test. 'Too hot to touch' is about 60C at the heatsink, so the transistor cores will be at maybe 80 or 90C. Most electronics are specified for 0-70C, those for cars from -20 to +85. Running components at elevated temperature degrades their operation... make you own mind up laugh

Neil

p.s. Injectors with impedances in the 10-14 ohm range are referred to as 'high impedance'. Don't even think about fitting 'low impedance' injectors with an impedance of around an ohm.


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Re: Bosch Injectors [Re: clanger] #1634136
22/07/2019 21:05
22/07/2019 21:05
Joined: Feb 2019
Posts: 56
Behind a blue gate
clanger Offline OP
Reaping the fruits
clanger  Offline OP
Reaping the fruits

Joined: Feb 2019
Posts: 56
Behind a blue gate
Thanks GrahamL. I thought about that and it might be a solution - I ran 1 liter of acetone through each injector at 3 Bar pressure, alternating constant flow and pulsing using a pp9 battery. It improved the spray pattern such that they are all now the same and on a cold start the engine now revs out to 1500 revs and then progressively drops down to 750 rpm idle. At that point I thought I might have fixed it, it was that good! However whilst cold start has improved impressively it has turned out to make no difference to the clearly observable injector tip leak frown So my concern is spending money on injectors that might just be past it - 124k miles.

Thanks Neil. What you have said all makes sense, I remember my V/IR and tbh I had not given a thought to the injector heat dissipation. My concern was the effect it might have on the ECU transistors but as you have described it might be worth pursuing. The only source I can find for the Lucas Denso @350 cc 12 Ohm at present is the US, the price is good but as usual they don't respond to mails. I'll give it a bit longer then give them a call.

Re: Bosch Injectors [Re: clanger] #1634268
29/07/2019 14:47
29/07/2019 14:47
Joined: Sep 2007
Posts: 548
Freedom
Master_Mariner Offline
Club member 583
Master_Mariner  Offline
Club member 583
Enjoying the ride

Joined: Sep 2007
Posts: 548
Freedom
If its of any use- on the issue of sonic cleaning -I had an injector issue last year - and had all of the injectors sonic cleaned/patterns checked etc. Maybe that made some of them healthier/spray better.

The non working one however still didn't work - they seem to have the tendency to be fine when cooler- but when hotter and the demand is high- so long hard driving - there at their weakest.

In the future this too is going to become (is starting to be) a real issue for coops. Be good if there was a go to solution...

Regards

MM

Re: Bosch Injectors [Re: clanger] #1634285
29/07/2019 21:30
29/07/2019 21:30
Joined: Dec 2005
Posts: 32,217
Hemel in the Hempstead
barnacle Offline
Club Member 18 - ex-Minister without Portfolio
barnacle  Offline
Club Member 18 - ex-Minister without Portfolio
Forum Demigod

Joined: Dec 2005
Posts: 32,217
Hemel in the Hempstead
We have thought for some time that the sonic welded joints have a tendency to stop working at elevated temperatures.


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Don't get no respect! [b]Coupe Fiat 1994-2000 - an owner's guide[/b] <-- clicky!

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