72-73 fuel injectors

[slofut]

What's the difference in 72 and 73 model 0280150024/36 fuel injectors? I'm (no, my mechanic) is having a terrible time sorting out a rich running problem. Stan Weiss site shows 24 and 36 identical in specs and 36.15 lbs/hr flow @43.5psi.

Now, this ebay listing shows these inj as replacements for 36's, but flow tested for 46.5lb/hr @43.5psi. The seller says theyre incorrect for '72 450sl but correct for '73 450sl.

https://www.ebay.com/itm/Set-of-8-Bosch-UPGRADE-Fuel-Injectors-1973-75-Mercedes-450-0000782723-783423/191547335251?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D225074%26meid%3D394386081b644 120b52229956f6214d1%26pid%3D100675%26rk%3D1%26rkt%3D15%26mehot%3Dpp%26sd%3D191547335251%26itm%3D1915 47335251%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DBosch&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Af4c85892-cc4d-11ea-98a1-74dbd1807171%7Cparentrq%3A77e8465f1730a86697061130fff2ac3e%7Ciid%3A1

Short story is I bought these injectors and the car ran great for a few min and then went way rich. Any help would be much appreciated.
Bill

[Tomguy]

All DJet 4.5s came with the 036 injectors, the 024 are direct compatible just came with a different hose style for Volvo I believe.
Flow rate for D-Jet injectors on Stan's site, I do not know where he gets the pressure data from, but look at the comparison on his chart for the 2.8 with D-Jet to the 4.5 with D-Jet. The 0-280-150-035 is rated at 30.5 at 29PSI. The 0-280-150-036 is rated at 36, but it claims 43.5PSI. I can say that one of those is wrong, for sure. I would say likely the 036 (and the 024 by proxy) is wrong, because D-Jet is designed for 29PSI operation (although I would suggest using 31-32 to prevent ethanol vapor lock).

These injectors you bought are listed at 46.5, but at 43.5PSI. If Stan's website is accurate, these injectors will flow way more than your 4.5's injectors do. If not, well, I don't know what to compare them to data-wise. Perhaps Bosch rates them at a different PSI than their own system was designed to supply them at? That doesn't make sense to me but I'm not a Bosch engineer.

No 450SL or 450SE(L) that I've ever seen (that uses D-Jet) has anything other than the 036 (or replacement 024) injectors.
No 3.5 engine I've ever seen has anything other than the yellow 034s.

[slofut]

Thank you Tom. Since early motronic and d-jet uses a preprogrammed map to supply fuel based on rpm's I'm thinking these injectors may flow too much fuel, a $400 mistake. Would a 350sl and a 450sl have the same injectors? Same guy has another set but listed for a '72, they're 200 bucks more but says they replace (again) 36's. Wth...

[Tomguy]

A 350SL (US-Spec with the 4.5) and 450SL would also be the 036, yes.

[Frank Reiner]

Originally Posted by slofut

What's the difference in 72 and 73 model 0280150024/36 fuel injectors? I'm (no, my mechanic) is having a terrible time sorting out a rich running problem. Stan Weiss site shows 24 and 36 identical in specs and 36.15 lbs/hr flow @43.5psi.

Now, this ebay listing shows these inj as replacements for 36's, but flow tested for 46.5lb/hr @43.5psi. The seller says theyre incorrect for '72 450sl but correct for '73 450sl. Short story is I bought these injectors and the car ran great for a few min and then went way rich. Any help would be much appreciated.

Originally Posted by slofut

Thank you Tom. Since early motronic and d-jet uses a preprogrammed map to supply fuel based on rpm's I'm thinking these injectors may flow too much fuel, a $400 mistake.

A couple of words on flow rates. The rating pressure of 43.5psi (3bar) is a standard for the purpose of comparing various injectors. In some systems it is also the operating pressure; in others not.
The book flow rate of 36.15lb@3bar is approximately twice the flow rate that would be used in any system other than D-jet for the anticipated horsepower. 250-300HP engines are frequently operated with 19lb@3bar injectors. When high flow rate injectors are operated at idle, the injector "on" pulse time becomes very short, as a consequence any error in input signals to the ECU that causes even a small increase in "on" time will result in a rich condition.
At idle the D-jet system relies heavily on the RPM signal, but not exclusively. Air and water temperatures affect the calculation, as does the MAP signal. An air leak in the MAP hose from the intake manifold can shift the mixture rich. Once the idle (closed throttle) contacts on the throttle body are opened, the primary load sensing signal is MAP, and the RPM signal controls the rate of injector pulsing, and the MAP signal controls the duration of the "on" time.

[801mbz]

I have not had many problems with those injectors. A gas analyzer is needed or you are just guessing. Points and dwell must be good no vacuum leaks vacuum advance working timing on spec or 5 advance. to pass IM retarding timing can lean it out some there is a knob on ecu that I had best results turning all the way lean then enriching mixture with allen screw on pressure sensor. Most cars have a tag with timing and CO spec. Is it rich at idle and 2500rpm? Or what?

[Tomguy]

Very good information as always Frank!
I agree with 801mbz that gas analysis should be done.

If you're too rich it might be possible to lean the new ones out (hence not a "$400 mistake") BUT the D-Jet window of adjustment might not be enough for this.

Personally I would have gone the other way in terms of flow rate, because lower-flow injectors often have a better mist, and D-Jet tends to be very rich to begin with. As an aside, if I were doing a D-Jet replacement, I would stick with injectors around 20-25lbs, while also running a much higher pressure, around 50PSI (like on modern cars). 25lbs at 50PSI would probably be more than sufficient for a boosted 4.5 I'd think, too.

[Graham]

Originally Posted by slofut

What's the difference in 72 and 73 model 0280150024/36 fuel injectors? I'm (no, my mechanic) is having a terrible time sorting out a rich running problem. Stan Weiss site shows 24 and 36 identical in specs and 36.15 lbs/hr flow @43.5psi.

015 and 024 are just predecessors of the 036 blue injectors. The 72 NA 350SL has same engine as a 73 NA 450SL and uses the same injectors.

Most of these Bosch injectors are NLA. But there are injectors available from Standard Motor Products that some have used for about $56/piece. https://tinyurl.com/y33vl7wf

Other option is to send old Bosch injectors to Witchhunter and have them cleaned and flow rated for about $25 each.

The injectors in the auction have a capacity of 396cc/min at 29psig. The Bosch 036 are rated at 310cc/min at same pressure according to Weiss site. There is a lot of conflicting data on injector capacities on-line, so this may not be accurate. But, if correct, it does seem to show that the injectors have about 27% too high a capacity. The MPS/ECU would have to be adjusted to suit. Other info I have confirms the 036 capacity at about 302cc/min at 29psig. But that too could be wrong. I have also seen capacities of 370cc/min at 29psi. So what to believe???

Ideally, you would want to increase the pressure to say 32-34 psig to prevent hot start problems. But the excess capacity of these injectors could make that problematical. Lower capacity injector would be preferable if pressure is increased.

Regarding an analyzer, these are not readily available. MB used to measure %CO, but there are no reliable CO meters available, at least for the DIYer. The alternative, is a wideband AFR meter that uses an O2 sensor in the exhaust. I installed one permanently with the sensor before the first muffler/resonator.

Once you have a means of measuring, you need to know just what to adjust. There is a knob on the ECU, but that only adjusts idle mixture. To get mixture under load correct, you need a meter that will read out while you drive. MB have specs for %CO under different operating loads. (%CO can be converted to AFR). To adjust the load mixture, you have to adjust the MPS. This is generally not recommended. But many cars have already had this fooled with (you can tell if the seal has been disturbed).

Your problem might be something else, but if you think you need to do this, get a reliable AFR for a couple of hundred bucks, install it so you can read it while driving and then adjust MPS in very small increments.

[Graham]

If you ever get to measure %CO/AFR, these are the numbers:

Full load shifter position S 3,000 rpm = 2% - 5%
Upper partial load position S, 2,500 rpm 300 mm Hg vacuum 0.1% - 0.5%
Lower partial load 3rd gear shifter position S, 1,500 rpm 300 mm Hg vacuum = 0.2% - 0.5%
Idle neutral, idle speed, oil at operating temp = 0.5% - 2.0%

Not easy to understand! For full load, I assumed a steepish hill. Or hold foot on brake while driving at 3000rpm in S. Overall, my car idles on rich side - AFR about 12.5 and 14-14.7 while cruising depending on load. I can lean it out, but these cars perform better with mixture on rich side.

%CO to AFR conversion

[Graham]

As an example of varying info on net about injector capacity. This site quote a capacity of 588 cc/min for the 036 injector based on testing at 3bar (43.5psi). They say that this is what they measured. https://injector-rehab.com/knowledge-base/flow-rates/ That would mean that the injector would provide 480cc/min at 29 psig! So what numbers do we believe?

I would go with Witchunter - the company that will clean and rate old injectors. Their number is close to same as the injectors in the auction. (404cc/min at 29psig) Injectors, then not likely the problem. For a start, make sure your coolant temperature sensor (TS2) is good based on resistance numbers in FSM and check that it is properly connected.

[JoshC450SL]

To Tomguy saying the 450’s came with 036. From what I can tell the injectors in my 74 450SL have 024.. they look original. I currently have 036 as their replacement because of it running rich I suppose and a misfire. Someone before me purchasing the car had replaced ONLY ONE injector and it’s a 036 as well the rest are 024. I wonder if that would be the case for the misfire or oil smelling of gas?

[Graham]

Originally Posted by JoshC450SL

To Tomguy saying the 450’s came with 036. From what I can tell the injectors in my 74 450SL have 024.. they look original. I currently have 036 as their replacement because of it running rich I suppose and a misfire. Someone before me purchasing the car had replaced ONLY ONE injector and it’s a 036 as well the rest are 024. I wonder if that would be the case for the misfire or oil smelling of gas?

The 024 and 036 injectors likely have the same capacity and performance. They just had slightly different design, such as the pintle caps. They both would have been blue. So no problem mixing and matching.

There are other things that could cause your misfire. For gas in oil, I would first check the ignition to make sure all plugs, wires and distributor are good. Maybe one plug is not firing and unburned gas is being left in one cylinder. Also do a compression test to make sure rings are good. There are several other things that can cause rich running. But one step at a time is best!