Author Topic: Fuel Pump volume (Read 11015 times)

Pinder · « **on:** January 14, 2016, 14:28:16 »

Ive been chasing an issue with my recently rebuilt 1970 280sl engine. I have rebuilt the fuel pump but suspect fuel volume is low for some reason. The symtoms are that the car while idling (cold or hot) will all of a sudden die. when I start it it starts right up. I measured fuel volume on the return line by the tank and its about .75 lt in 15 secs. I also took a measurement by the IP and its closer to 1lt in 15 secs there. If I measure it right after the pressure regulator its .75 lt.

Any thoughts on the fuel volume? does this look like the pump is working OK or not?

Tyler S · « **Reply #1 on:** January 14, 2016, 15:50:03 »

Delivery sounds ok. How about the electrical portion of the pump. If you can duplicate this issue I would suggest putting a fuel pressure gauge near the IP inlet and watch it when the car stalls out. If it drops out then check for power at the pump during the stall. If it still has power with no pressure, check the pump brushes.

Pinder · « **Reply #2 on:** January 14, 2016, 16:26:59 »

Tyler,

Sounds like a good plan. I did change brushes on that pump but my soldering iron was not very good and i just barely completed the solder. Maybe a weak connection. Ill check it out on Saturday.

ja17 · « **Reply #3 on:** January 15, 2016, 00:51:07 »

Hook up a pressure gauge to the system. Watch to see if the fuel pressure drops off right before the engine stalls. If not, it's probably not a fuel delivery problem. Once fuel pressure falls below 9psi. , bad things begin to happen. Healthy systems carry between 12 and 16 psi.

Benz Dr. · « **Reply #4 on:** January 15, 2016, 19:09:11 »

I agree with Joe but sometimes getting 10 + PSI can be a real challenge.

Volume and pressure sort of follow each other so if you have 10 PSI and 1 liter per second your engine should run OK.

Did you check that you have full return all the way back and through your fuel tank?

Pinder · « **Reply #5 on:** January 15, 2016, 23:22:30 »

think i was on a wild goose chase. Pressure is above 10 PSI and when it quits pressure is the same. So Now it looks like the issue is with the transistorized ignition module under the battery. Not getting spark or it goes in and out. I'm in the process of eliminating it and see if it resolved the issue.

ja17 · « **Reply #6 on:** January 16, 2016, 15:04:32 »

Sometimes it is just the coil. The electronic ignition is a good system as long as the expensive electronic "box" is still good. If you change over to std. you need to change the wiring around a bit, replace the coil and the ballast resistors.

Pinder · « **Reply #7 on:** January 16, 2016, 21:45:59 »

So the latest update. disable the transistorized ignition module and hooked it up like a standard ignition using the 6 ohm resistor only. It still didnt start. Then I swtiched the distributor cap ffrom my other car and it fired up right away. Turns out the distributor cap was totally worn out.

Now since I have disable the transitor module is it OK to run it with the way I now have it ? will i need to replace the blue coil with a different one? What is the down side of running like this.?

I will now order a new cap and rotor (which I should have done earlier) and also reconnect it back to how it was before as I think thransistor module is probably ok.

Tyler S · « **Reply #8 on:** January 17, 2016, 03:59:02 »

Quote

think i was on a wild goose chase.

No, not a wild goose chase. You correctly ruled out a fuel delivery problem.

Part of diagnosing is narrowing down your potential culprits.

Naj ✝︎ · « **Reply #9 on:** January 17, 2016, 11:20:01 »

Quote from: Pinder on January 16, 2016, 21:45:59

Now since I have disable the transitor module is it OK to run it with the way I now have it ? will i need to replace the blue coil with a different one? What is the down side of running like this.?

Personally, I would keep the transistorised setup and the blue coil. It gives a much stronger spark.

If you decide not to use the transistorised setup, you will need to change down to a red coil, otherwise the current thru the points will burn them out in no time...

Just my $0.02...

naj

Pinder · « **Reply #10 on:** January 17, 2016, 15:13:40 »

I can conclude for a fact that the points burn out very quickly. I put a new cap on and ran fine for a while and then tried to start and nothing happened. Had to use some fine sandpaper to clean points and re gap and then it ran fine. So will switch back as this blue coil is screwing up the points. Will switch back to how the wiring was after my morning cup of tea.

ja17 · « **Reply #11 on:** January 17, 2016, 16:08:16 »

Yes the factory transistor set up works well (85% stronger spark), and easier on the ignition points. It must be hooked up correctly also to work well. When changing to standard ignition be sure to change the coil and the ballast resistor. The coil you use will specify which ballast resistor to use. With a red coil use a 1.3 ohm ( it has a red band). The wiring is changed also as the ignition coil is no longer directly connected to ground (as on the transistorized). In a pinch you can use the std. red coil and take both two original ballast resistors from the transistor ignition (0.4 ohm and 0.6 ohm) hook them up in series to form a 1.0 ohm resistance. This will work till you get a 1.3 ohm resistor. I always thought is strange that the expensive transistor box was located directly under the acid battery !

Pinder · « **Reply #12 on:** January 17, 2016, 16:43:59 »

This is very good to know.

Ok so just got back from the garage and hooked it all back up with the transistor module. Everything fired up perfectly. So the final conclusion is that the Cap was worn or wrong cap on it. I got a cap from Napa (last one in stock) and it works great! Thanks for every ones help nailing this. Now I can move on to getting the slave and mast clutch cylinders in plus that painfully unnecessarily expensive master to slave hose.

Benz Dr. · « **Reply #13 on:** January 17, 2016, 22:41:19 »

Quote from: ja17 on January 17, 2016, 16:08:16

Yes the factory transistor set up works well (85% stronger spark), and easier on the ignition points. It must be hooked up correctly also to work well. When changing to standard ignition be sure to change the coil and the ballast resistor. The coil you use will specify which ballast resistor to use. With a red coil use a 1.3 ohm ( it has a red band). The wiring is changed also as the ignition coil is no longer directly connected to ground (as on the transistorized). In a pinch you can use the std. red coil and take both two original ballast resistors from the transistor ignition (0.4 ohm and 0.6 ohm) hook them up in series to form a 1.0 ohm resistance. This will work till you get a 1.3 ohm resistor. I always thought is strange that the expensive transistor box was located directly under the acid battery !

red coil should use a 1.8 ohm ballast

Pinder · « **Reply #14 on:** January 17, 2016, 23:19:18 »

Ill see how it drives with the original setup and new distrib Cap. Seems ok right now in idle. It runs fine now and does not randomly die. But If it screws up again i will look into the 123 ignition.

RoyB · « **Reply #15 on:** January 21, 2016, 18:52:20 »

I would like to ask a question regarding the fuel pressure and volume test you did. I seem to be having a similar problem, and want to do this correctly. The pump runs but the car is hard to start. It runs acceptably, but not right. Where did you disconnect the fuel line in order to verify the fuel volume from the pump? At the tank or in the engine compartment? Photos would help if you have them. Thanks

Pinder · « **Reply #16 on:** January 21, 2016, 19:20:00 »

Roy I connected it from the goose neck hose coming out of the fuel pump which is the line that would feed the FI pump. This is from the tank side. I was going to try the test from the line that goes out of the fuel filter into the fuel injection pump but didnt have the right fittings to do that. Basically i just used some fuel lines and a T fitting to insert the pressure gauge.

It turned out when my car was running rough and then quiting it was actually a spark issue with a incorrect distrib cap. after change of cap it ran much better. Howver I am still losing spark intermittently and now suspect I had two problems. Distributor cap and also the transistorized ignition module which seems to stop giving out spark intermittentaly.

RoyB · « **Reply #17 on:** January 22, 2016, 20:20:58 »

Thanks, that helps. I have purchased new plugs, distributor cap and rotor but want to start with fuel delivery first.

Pinder · « **Reply #18 on:** January 23, 2016, 06:24:56 »

Good move on the cap. That was what was the biggest problem i had. I still have some strange electrical issue. I caved in and ordered the crane 3000 unit to get rid of the points and the old transistorized ignition. Ill report back if it fixes my intermittent no spark issue. Its very random but happens enough were i cannot trust it to start.

Tyler S · « **Reply #19 on:** January 23, 2016, 07:31:19 »

Pinder, Think about also changing the coil if your going with the crane. I am using the Red coil with no ballast resistor. Good strong spark and it got rid of an intermittent miss. Let me know if you need any install pictures. The kit is a bit fiddley and has changed a little since the guide was posted here.

Pinder · « **Reply #20 on:** January 23, 2016, 12:54:17 »

when I get the kit if im unsure of anything ill definitely ask for help. I ordered two kits one for each car im working on. I was thinking of getting the a new coil so that all the igintion side is basically new.

ja17 · « **Reply #21 on:** January 23, 2016, 16:29:16 »

Right Dan, sorry for the "brain fade" 1.8 ohm ballast resistor with the red coil. I have used the 0.4 ohm resistor and the 0.6 ohm resistor, (wired in series for a total 1.0 resistance), to temporarily replace a 0.9 ohm resistor in the past.

Pinder · « **Reply #22 on:** January 30, 2016, 01:22:57 »

Tyler,

Which coil did you use ? is it Bosch 0 221 119 030. I have the crane system in and its running well but my spark may be weak. pulled spark plus and they are dry and black sooty deposit. I want to make sure spark is good before i mess with the fuel mixture.

thanks

Pinder

Tyler S · « **Reply #23 on:** January 30, 2016, 21:55:05 »

Pinder, I am using the Bosch 0 221 119 030 because it has no internal resistance as stipulated in the xr3000 instructions. I left the ballast resistor in place for aesthetic reasons and ran a jumper wire between the 2 screw terminals on the back side of it. Using NGK BP6ES non resistor plugs gaped at .035. I have a set of BP5ES plugs on hand if I need them, need to put some miles on it first. I do have resistive wires installed as I think having non resistive wires might be too much for the plugs. Good strong spark at the plug leads.

Benz Dr. · « **Reply #24 on:** January 30, 2016, 22:03:26 »

Quote from: Tyler S. on January 30, 2016, 21:55:05

Pinder, I am using the Bosch 0 221 119 030 because it has no internal resistance as stipulated in the xr3000 instructions. I left the ballast resistor in place for aesthetic reasons and ran a jumper wire between the 2 screw terminals on the back side of it. Using NGK BP6ES non resistor plugs gaped at .035. I have a set of BP6ES plugs on hand if I need them, need to put some miles on it first. I do have resistive wires installed as I think having non resistive wires might be too much for the plugs. Good strong spark at the plug leads.

I've been using BP5ES with good results. I don't think you would have a problem with low resistance plug wires - spark plugs can take a lot of voltage and I think the red coil is only 26KV.

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Author Topic: Fuel Pump volume (Read 11015 times)

RoyB

RoyB