Petrol Injectors

Joined
Jun 18, 2009
Messages
11
Reaction score
0
Location
birmingham, uk
Your Mercedes
1988 300 CE
I'm slowly working my way through niggles on my new 1988 300CE, the latest I'm looking at could possibly be an injector problem. The trouble is it does'nt start as quick as I think it should (hot or cold) When it does fire, sometimes it only fires on four or five cylinders for a few seconds, before running normal. Now I know that I read about the injectors leaking petrol into the engine whilst it is switched off? So my questions are, can these injectors be fixed, can I find which one is at fault, and any recommended suppliers. I've put some injector cleaner in the tank, but as usual with these bottle cures, it had no effect. Feel free to tell me I've got this completely wrong, I'm still used to carbs. thank you
 

kth286

Senior Member
Joined
Nov 4, 2002
Messages
3,067
Reaction score
2
Your Mercedes
E320 Coupe 95
You are probably working along the correct line.

Before you start the engine one day, take all the plugs out and shine a torch down into each bore in turn.

you will see the shiny petrol on the pistons of the cylinders that are leaking.

Also a tip, if you unplug the cold start device, you will likely find the car will start much better and save the battery.

The cold start device injects even more petrol into the bores and helps flood the car worse.

When you have fixed the injector problem, reconnect the cold start.
 

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
i too feel you may well be right.

nb; cold start injector should not fire when coolant above 15deg c - ie now.
 

LYNALL

Senior Member
Joined
Aug 7, 2003
Messages
315
Reaction score
0
Location
Kent
Remove and get them ultrasonic cleaned and checked, had mine checked no fault found bloke said very rare they see merc injectors.



Lynall
 

kth286

Senior Member
Joined
Nov 4, 2002
Messages
3,067
Reaction score
2
Your Mercedes
E320 Coupe 95
Remove and get them ultrasonic cleaned and checked, had mine checked no fault found bloke said very rare they see merc injectors.



Lynall

Yours are electrical, his are mechanical which do leak.
 

LYNALL

Senior Member
Joined
Aug 7, 2003
Messages
315
Reaction score
0
Location
Kent
Okay dokey ill go away then!

Cant they still be cleaned? after all an injector is just an injector.

Jetronic? bosch new.


Lynall
 
Last edited:

television

Always remembered RIP
Joined
Mar 14, 2005
Messages
164,073
Reaction score
332
Age
86
Location
Daventry
Your Mercedes
2002 SL500, 216 CL500, all fully loaded
Okay dokey ill go away then!

Cant they still be cleaned? after all an injector is just an injector.

Jetronic? bosch new.


Lynall

Yes they can be cleaned and there are many firms that do this service. Once an injector becomes dirty the spray angle and pattern changes and the fuel can fail to atomize correctly
 

television

Always remembered RIP
Joined
Mar 14, 2005
Messages
164,073
Reaction score
332
Age
86
Location
Daventry
Your Mercedes
2002 SL500, 216 CL500, all fully loaded
I was thinking about this while cleaning the window :D:D

Leaking injectors into the bore,,, how much can actually leak,at idle say 700RPM they are opening 350 times a minute.,,so can they leak to make any difference, they cannot drip readily as the fuel in the pipe will hold the fuel back to a certain degree

Just thoughts that is all
 

turbopete

Senior Member
Joined
Feb 4, 2009
Messages
14,204
Reaction score
328
Age
46
Location
Spennymoor
Your Mercedes
2010 '60' Ford Mondeo 2.0TDCi Zetec (sorry)
I was thinking about this while cleaning the window :D:D

Leaking injectors into the bore,,, how much can actually leak,at idle say 700RPM they are opening 350 times a minute.,,so can they leak to make any difference, they cannot drip readily as the fuel in the pipe will hold the fuel back to a certain degree

Just thoughts that is all

but it would take a few moments to get the excess fuel out of the bores after standing, a bit like a flooded engine. just a thought
 

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
leaking jetronic injectors are a known cause of slow starting. usually between a few minutes and a couple of hours after stopping, ie not on cold start.
 

kth286

Senior Member
Joined
Nov 4, 2002
Messages
3,067
Reaction score
2
Your Mercedes
E320 Coupe 95
leaking jetronic injectors are a known cause of slow starting. usually between a few minutes and a couple of hours after stopping, ie not on cold start.

Why not on cold starts ????????????????????
 

television

Always remembered RIP
Joined
Mar 14, 2005
Messages
164,073
Reaction score
332
Age
86
Location
Daventry
Your Mercedes
2002 SL500, 216 CL500, all fully loaded
Why not on cold starts ????????????????????

Could be expansion within the injectors,,also you have the cold start valve/injector spraying in more fuel.

See what Alexander says
 

stever

Senior Member
Joined
Jun 20, 2005
Messages
174
Reaction score
0
Why not on cold starts ????????????????????

Warm start on the jetronic system relies on residual fuel pressure being maintained - which won't happen if the injectors or accumulator are leaking. Cold start uses various devices (warm up regulator, cold start valve, auxiliary air valve) that remove the need for fuel pressure.
 

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
yes, all of the above. however the reason the leaking injector causes poor starting in the approximate time frame i mention, is down to puddling of fuel in the manifold and consequent flooding - hence the lumpy running after laboured start.

over time the fuel pressure will drop to 0.0bar (in this scenario) as the accumulator empties, then eventually (by, say, the next morning) the puddled fuel will have evaporated through the throttle body and air filter etc.
 
OP
F
Joined
Jun 18, 2009
Messages
11
Reaction score
0
Location
birmingham, uk
Your Mercedes
1988 300 CE
  • Thread Starter
  • Thread starter
  • #15
I'm still reading up on this before I remove the injectors for cleaning/cheaking. Am I right in that mine is a Bosch KE-Jetronic system, and is open loop if I have no lambda sensor? Any suggestions on where to buy replacements if they are stuffed?
 

Number_Cruncher

Senior Member
Joined
Oct 10, 2007
Messages
1,806
Reaction score
2
Your Mercedes
1995 W124 E300D TE
Injectors on K and KE jetronic are really dumb devices - all they are is a sprayer. The metering and cut-off function is all done at the distributor / metering head.

There's no pulsing on and off so many times per second, they are either spraying, or they're not.

To check them, remove them from the manifold, and point them into jam jars.

Short out the relay to run the pump.

You should see nothing.

Move the air flap by the metering head, and they should spray. Let the air flap go, and they should all stop.

Cold start injectors are prone to sticking open, and dribbling fuel in even when they're supposed to be switched off.

If you find one that looks odd, swap it with a neighbour and repeat the test to identify whether the fault is in the injector, or in the metering head.
 
OP
F
Joined
Jun 18, 2009
Messages
11
Reaction score
0
Location
birmingham, uk
Your Mercedes
1988 300 CE
  • Thread Starter
  • Thread starter
  • #17
So can I test the cold start valve for leakage at the same time with it removed as well? Also, why can't you just put ignition on rather than shorting fuel pump relay?
 

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
mr tin-of-pie, yes and yes. also, don't know where.

number worrier, all true but the cold start on ke-jet is usually no trouble. cold starts on earlier cars, especially d-jet and mechanical are more likely to play up.

f.b. to avoid further confusion i was replying to your earlier post.
 

Number_Cruncher

Senior Member
Joined
Oct 10, 2007
Messages
1,806
Reaction score
2
Your Mercedes
1995 W124 E300D TE
>>the cold start on ke-jet is usually no trouble

On some Bosch systems with thermo time switches and cold start injectors (K and L jetronic) I've seen dribbling cold start injectors. In some cases it's slight, and can be compensated in a rough bodge way by tweaking the main system's mixture.

It tended to show up more on L jetronic cars, because the range of possible mixture adjustment is nowhere near as wide as K.

The cold start injector can be tested just like the other injectors - so, it's simple and cheap to check to make sure it's off when it should be off.

The fuel pump only runs for a few seconds after turning the ignition on - to get it running for longer, you'll need to temporarily short the terminals on the fuel pump relay.
 

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
>>the cold start on ke-jet is usually no trouble

On some Bosch systems with thermo time switches and cold start injectors (K and L jetronic) I've seen dribbling cold start injectors. In some cases it's slight, and can be compensated in a rough bodge way by tweaking the main system's mixture.

It tended to show up more on L jetronic cars, because the range of possible mixture adjustment is nowhere near as wide as K.

i guess this means we concur then number eater. ke-jet has no thermotime switch.
 


Over 100 branches Nationwide, More than 114,000 Parts in Stock, The UKs Largest, and Fastest Growing Parts Supplier,please see MBO Members’ Area for discount codeEuro Car Parts Ltd
Top Bottom