Fuel delivery / afm chart

[nahuston]

Today seems to be the day of fuel related questions here - I'll add another one. I'm tracking down a high rpm cut out on my 230sl. A quick background - I never drove this car when it was running "right" so I don't have a great baseline but injection pump was rebuilt a few years ago and not run much since. I have renewed ignition components and started with a clean fuel tank/ new fuel. I have also replaced some linkage ball ends and ajusted the linkage per the linkage tour. At about 4k rpm the engine starts missing/ backfiring and will not rev higher, almost acts like it is hitting a  rev limmiter. I hooked up my wideband o2 sensor / datalogger and I'm a little puzzled by the results. At full throttle from idle through through 1st and 2nd gear you can see that it goes way rich and then right at 4k rpm when it starts to cut out it goes WAY lean. I then hooked up my fuel pressure gauge (to the CSV feed line, I assume that is ok) and it is at about 10psi all the time, even at 4k rpm when it starts to miss. From what I've read on here 10psi is too low. I have much more experience with EFI but I was surprised that if 10psi is too low it would be able to over-fuel at low RPMs and yet not show a dip in pressure at high RPM, although I'm not measuring pressure at the the "rail" like I would in an EFI car. Thoughts? Thanks!

[nahuston]

attached jpeg of graph as it may be easier to view than pdf

[nahuston]

Update - I changed the fuel filter and screen again, they looked fine though. I clamped off the return line from the regulator and my pressure went up to 15psi. It revs better over 4k now but is running too rich at idle/ low rpm. Is the regulator adjustable?

[garymand]

The flow rate of 1 litre per 15 seconds should be the flow rate measured from the return line at the tank end.  I looked but couldn't find a pressure.  at 1st I thought you had a spark problem, points or plugs.: missing at 4K.  But you changed something in the gas system and it got better.  Saying you are onm the right track.  The chart is crazy.  Do I understand?  the rpms go up to 4300 and drop to 1800 theen up again and back down?  The A/F go3es bang bang stop to stop, then gomes in almost good then shoots to bang again? 

[mbzse]

..../.... Is the regulator adjustable?

No. Inside is a rubber diaphragm and a spring - is this unit ok in your car?

Pressure from fuel pump, before fine fuel filter canister, should be 0,8 to 1 bar [11.5 to 14.5 psi]
However, the 1 litre in 15 sec specification is what is mentioned in the workshop manual
/Hans in Sweden

[garymand]

Once you get this running right, post a few graphs of what the a/f should be like.  I have an O2 sensor on mine and It is driving me nuts: when cruzing with little to no load, the a/f goes rich below 12.  the less load, the more rich.  I can only think my pump cam is for a motor that pulls a bigger car as I would think the cam would reduce gas when the throttle is eased back as i cruze at 3500rmp.

It does drop to lean when coasting down a hill and the trottle is backed off a lot.

I do have the FIP adjusted for a little rich for all the specs.  the motor puts out its best performance there.  I can increase the rod clicks and bring all into spec, but the performance is much milder.

[nahuston]

ok- first to answer the question about the graph. black is rpm, purple is afm.  You can see the rpm go up to about 4000 then plateau off (because it wont rev any further right now) then I shifted into second gear and you see the revs climb again.  But yes, at throttle tip in and until about 4000 rpm my car goes off the scale rich and then at 4000 rpm it goes off the scale lean. I dont know that the quick spike into range means much, its probably just an error. I thought that maybe it was ignition as well but I'm using an inductive rpm pickup and I think I would see the rpm graph drop off or become intermittent if it was not firing, instead it has a steady curve. When I first got it up and running it was running way rich at idle and fouled a set of plugs. I changed them and when I re-checked them today after driving the car several times they actually look pretty decent if not a bit lean.

Ive done the flow test too and it is in spec - i've been trying to avoid messing with any of the injection pump settings as they all have paint marks on them from when it was rebuilt. The only thing I have messed with is the knurled knob on the back of the pump for idle mix with limited success. This thing is giving me fits because one day it will fire right up and idle/ rev great (albeit not over 4k rpm) and then the next it idles too high or barely idles at all. Every now and then it will rev fine to almost 5k and every now and then it starts sputtering at 3500. Fuel pressure stays consistent at 10-11psi.  I may have to bite the bullet and take it to someone who is very familiar with these injection systems but I would like to figure it out on my own and be able to keep it running right in the future.

Compression is consistent at 155 across the board and all of the ignition components are new except for the coil. Vacuum advance is working. I still need to check timing but I don't think thats the issue

I am picking up another 230sl tonight, its an automatic but I will datalog it and post the graph for comparison, I'll also check fuel pressure at the same port on it to compare.

[nahuston]

Oh! and just to add one more piece to the puzzle. Before ever starting the car I checked the oil in the injection pump, it was clean and at the proper level. Now (a couple weeks later) I noticed a substantial oil leak out of the cap on the pump. I unscrewed the t-handle dipstick and several ounces of oil came streaming out (engine not running). It was thick and black. How did the injection pump go from clean oil at the right level to way overfilled on an early 230sl with a self contained oiling system?!?

[ctaylor738]

This sounds to me like a bad coil or something related to ignition.  I worked on a 230SL that did almost exactly the same thing. It would go to 6000 if brought up slowly but lay down and die at 4000 under full throttle.  A new coil fixed it instantly.

I worked on a 250SL with a Pertronix that had a similar problem but at lower RPM and not necessarily at full load.  It had an ancient capacitor on the positive side of the coil.  I removed it and it was like a new car.

I can't explain the results of your A/F meter, but it seems to me if you were running out of fuel, you would get some backfiring.

I am currently working on a 250SL with a brand new fuel pump, rebuilt injection pump, and a new regulator/modulator.  It does 1.2 liters in 15 seconds but has 11 psi at the CSV with the return open, and 15 with it pinched shut.

Good luck,

CT

[garymand]

Good clue.  Now we have something.  I'm not expert on the 230 but I know the 250.  I think there is overlap with late 230.  The FIP has a separate isolated oil supply around the centrifical govenor.  That is what the dip stick and red cap are about.  The pumps are, I think, given engine oil to keep gas from getting past the pumps.  There should be a little pipe delivering oil to the piston area,  I'm not sure how or if the oil flows through. On later models the oil spills out the front into the chain gallery.  

I think the seal between the front and back has failed or the outlet is blocked.  The engine oil is backing up into the govenor side.  

The other symptom I read was the inconsistant idle as the FIP should easily adjust the idle.  Check the manual on the FIP, I vaguely remember this type of issue but sorry, don't remember reading a solution.  Since you have access to another but good running 230, pull the pump! Do a quick swap in with a known good device.  

I also don't understand the extreme swings in a/f: I can see that on FT the FIP is dumpinf in gas.  that can explain the rev limit, but then why does it swing to no gas with the motor reving from 3.5k to 4k.  But I do like the dip at that point to near stoic at 4.6k, but then it startd dumping in gas again and the motor limits again.  I do like the fact that it repeats.  That gives us some focus. But it could be ignition with un burned fuel due to internittent/poor spark.  Pull the other coil, then the disty, both pretty easy and quick.

I'd say pull the pump, sub in the good one.  If the good pump fixes it. send the fip back to the rebuilder with history and ask for help. The engine oil in the regulator area is not correct on the 230 or 250.

[ja17]

I agree with Chuck,  check the coil.   

[nahuston]

This is helpful! After reading your replies I started to think...  If the spark is weak it would show up as a rich condition UNTIL it can no longer ignite the mixture. The o2 sensor can meter exhaust gas but not unburnt fuel, it would see it as air and ignore the raw gas thus showing a lean condition. The inductive pickup on my datalogger would still be seeing ignition (rpm) because the coil is still firing, just not firing strong enough to fire the plug! New coil on the way, I'll keep you updated!

[nahuston]

Coil and condensor has fixed my high rpm cut out issue! Now I have a pretty consistent dead miss on #6, it was there some before but now its really obvious... Changed the plug, swapped the wire, checked compression, confirmed spark. Ugh, its never ending. I may have the mixture off enough that its not getting fuel. I'll start checking that. Is there a way to test the injector for proper flow/ spray?

[ctaylor738]

If you're not in a hurry, you can pull your injectors out and send them to me.  I have one of the old Bosch testers.  Cost is return shipping and a can of BG44 which I use for testing and cleaning.  PM or email for address.

You can also move the injector to another cylinder and see if the miss moves to that one.

[ja17]

If your car is an automatic, then a rupture in the modulator diaphragm will cause auto trans fluid to fowl out # 6 spark plug and cause a miss in that cylinder. Also check the  #6 spark plug  cable end with an ohm meter.

[jeffc280sl]

As it has been said before check everything before trying to adjust the FIP.  It is tedious and requires a manifold air pressure sensor, data logger, afr inputs and a lap top/  I have an old post that describes what I went through.  It was worth it to get everything right first.  I'd say it easier to sent the pump out for calibration.  More satisfying I think not.

[nahuston]

Its running great now. They say that most carburetor problems are electrical (ignition) and I guess the same holds true on the 113. I did of course have to go through and get all of the linkage set right and mess with the idle mixture. I'm running a little rich but its running so damn good now that I'm hesitant to mess with anything else. Setting timing and dwell fixed my #6 miss somehow. When i get a chance I will post an AFM chart with it in its current good running state. Thanks for all the help!