[Neil Belt]

Hello everybody. Thank you for the great information that has been posted. I have spent a lot of time reading through all of the posts, especially the encyclopedia germanica sticky. I want to start off by asking what browser is best for this website. I usually spend 5-10 minutes trying to load the page I want I am working on tuning my 72 350sl right now and I am getting a lot of misfires. Timing is set 5 degrees BTDC (about 27 total advance @ 3k rpm), but it jumps with misfire. Dwell is at about 33 and all injectors seem to fire just fine (I listened to them). She seems to misfire a lot before reaching operating temp, but not as much afterwards. Plugs are a little white, I set them at 0.032" Ecu is set to all the way rich, she misfires more if set leaner. I did check the air temp sensor and water temp sensor, but map.... there isn't a test for it? Right now I plan on cleaning the injectors and then replacing the fuel filter. Fuel pressure is also good, 31 psi. Can I soak the injectors in carb cleaner, or will that destroy the electronic or rubber parts? I haven't seen much information on the best way to clean them yet. I am also going to replace the soft top and paint the hood. I don't like the way the soft top bows up right now (on the back), is there a thread that deals with this? What is the best manufacturer for the soft top?

 

[Fonzi]

Welcome! Please fill out your profile.

Browser: I used Firefox with an ad and pop up blocker. The ads have gotten out of hand.

5 BTDC is correct at idle if you have no vacuum on the distributor. Vacuum at idle should be eliminated if AC is on, but when on, it should retard the timing 10 degrees to 5 ATDC.

Injectors can be soaked and "cleaned" in a vibrating jewelry cleaner I think. I've never tried myself.

There are threads on soft top replacement, but I assume you have stitching or the connection to a bow undone. Just don't damage the frame. Tops are only a couple hundred bucks if you DIY, normally about a thousand if you go to a pro.


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[cushjbc]

D-Jet tuning: Your ECU is operating on assumptions that you are read up on. The best overall tuning concept I've read recommends bringing ignition, vacuum (air), then fuel delivery up to spec - in that order.

ECU rheostat only controls mixture at idle defined by TPS closed. Has your MPS been tampered with? If the protective black domed cap is gone, the assumption has to be made that it has. MPS tuning is the absolute last item to ever touch - independent mechanics and DIYers violate this a lot.

Many of us are advocates of Pertronix to eliminate problems caused by worn distributor bearings and resultant worn contact points; never worry about dwell again.

We can talk engine harnesses later . . .

 

[Ianwright40]

I recently watched a You tube video. On there a guy was using Ethylene Glycol to clean small engine parts and router bits.... I can't say if this will work on injectors but I am considering trying this out with a small ultra sonic cleaner.

 

[MBGraham]

Ecu is set to all the way rich, she misfires more if set leaner. I did check the air temp sensor and water temp sensor, but map.... there isn't a test for it? Right now I plan on cleaning the injectors and then replacing the fuel filter. Fuel pressure is also good, 31 psi. Can I soak the injectors in carb cleaner, or will that destroy the electronic or rubber parts?

Read the section in EGV107 about setting the Throttle Position Switch (TPS). Make sure it is set properly so that it will signal to the ECU that you are at idle. You should be able to set knob in middle or range and fine tune idle mixture by going a click at a time followed by short burst of throttle.

Resistance testing of MPS is covered in the shop manual. Also check with Mityvac or similar that it will hold say 20" of vac for 15-30min. To test if it is working properly and make adjustments, you need an exhaust analyzer or a wide band AFR meter (I could never get my car right until I installed an AFR meter, but hardly anyone here has one!)

Probably not your problem, but you can immerse the injectors in carb cleaner. There are small screens on the inlets. You can remove those for cleaning by screwing in a suitable sheetmetal screw and pulling to extract. I set up a kind of crude system to flow test the injectors using my pressure brake bleeder. I think it is in the Comprehensive guide in the stickies. Later, I did 4 at a time using spare fuel rails and compared the amounts collected. At first I used Seafoam to clean, then carb cleaner. For flow testing I used clear mineral spirits/Varsol (not gasoline!)

Don't know why you are getting misfires. Usually timing or ignition problem. Follow what Cush said and get things in good shape firts (Sounds like you are well on your way). Pertronix eliminates points as a potential problem - covered in Stickies. Make sure rotor and cap are aligned. Check for damage to contacts in cap.

 

[Neil Belt]

Thank you all for the useful information. Winter is coming and I will have more time to start addressing the problems that I have had. I believe that my misfires are ignition related. My tach started dropping recently, coordinating with a loss of power that is noticeable at highway speed or any decent amount of acceleration. I will replace the points with a Pertronix set up this winter and hopefully find out why I'm loosing spark as well. The tach drops every 2 seconds or so and has a major cut out about once every 5 minutes that causes a decent loss of power very briefly.

 

[Neil Belt]

Read the section in EGV107 about setting the Throttle Position Switch (TPS). Make sure it is set properly so that it will signal to the ECU that you are at idle. You should be able to set knob in middle or range and fine tune idle mixture by going a click at a time followed by short burst of throttle.

Resistance testing of MPS is covered in the shop manual. Also check with Mityvac or similar that it will hold say 20" of vac for 15-30min. To test if it is working properly and make adjustments, you need an exhaust analyzer or a wide band AFR meter (I could never get my car right until I installed an AFR meter, but hardly anyone here has one!)

Probably not your problem, but you can immerse the injectors in carb cleaner. There are small screens on the inlets. You can remove those for cleaning by screwing in a suitable sheetmetal screw and pulling to extract. I set up a kind of crude system to flow test the injectors using my pressure brake bleeder. I think it is in the Comprehensive guide in the stickies. Later, I did 4 at a time using spare fuel rails and compared the amounts collected. At first I used Seafoam to clean, then carb cleaner. For flow testing I used clear mineral spirits/Varsol (not gasoline!)

Don't know why you are getting misfires. Usually timing or ignition problem. Follow what Cush said and get things in good shape firts (Sounds like you are well on your way). Pertronix eliminates points as a potential problem - covered in Stickies. Make sure rotor and cap are aligned. Check for damage to contacts in cap.

MBGraham. Thank you very much for your response as well as your extensive sharing on this forum. I decided to replace the points with the Petronix kit and the coil as well, following your posted material. The car is running almost perfectly now I will still clean injectors and check spray patterns and do some minor tuning, but I am very happy with the new ignition What would be a good spark plug gap for the higher coil output of the flamethrower? I will add a air/fuel sensor soon as well and adjust the car for a little better mpg if possible. I'm guessing that fuel pressure is the only way to do this? Now it is time to start addressing the cosmetic issues. I have a new soft top and I'm going to strip the hood and hard top for paint soon. That is going to take some time and money. Lol But... I get to drive plenty in the mean time.

 

[MBGraham]

What would be a good spark plug gap for the higher coil output of the flamethrower? I will add a air/fuel sensor soon as well and adjust the car for a little better mpg if possible. I'm guessing that fuel pressure is the only way to do this? Now it is time to start addressing the cosmetic issues. I have a new soft top and I'm going to strip the hood and hard top for paint soon. That is going to take some time and money. Lol But... I get to drive plenty in the mean time.

Glad to hear the Pertronix helped. Although the Flamethrower coil has capability of higher voltage, actual voltage, as you likely know, depends largely on spark plug gap. However, I have seen no reason to increase gap from manufacturer's specs. For example 0.32 on NGK BP6ES plugs. There are many opinions on these things and I have never seen any hard info regarding relative performance using different of types of plugs and gaps.

Regarding air/fuel ratio measurement, you need a wide band O2 sensor in exhaust and a meter that reads out AFR. I installed a permanent meter. There are portable units. Don't get a cheap (non wide-band) meter.

Adjusting fuel pressure will affect your air-fuel ratio. However, even at the specified pressure of 2Bar (29psig), the cars can have hot-start problems. I have mine set at about 33psig which would normally give a richer mixture (low AFR). I compensated for that by adjusting the MPS (and the ECU at idle). Mixture is now within the specified ranges for %CO (There are tables for converting %CO to AFR) but on rich side at idle, which helps with hot starts.

Good Luck with tuning your car and the cosmetic upgrades!

 

[Fonzi]

Don’t discount the timing when considering both emissions / AFR and MPG.

You can also investigate the spray pattern you are getting from each injector.


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[MBGraham]

Don’t discount the timing when considering both emissions / AFR and MPG.

You can also investigate the spray pattern you are getting from each injector.


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Fonzi, You probably don't see all the posts on your phone, but in #1, Neil said he had timing set to 5BTDC idle, 27BTDC at 3k rpm. Just about right!

I am sure it is a good thing to have a good spray pattern. But really those djet injectors just squirt streams of fuel into the intake manifolds. Two fire at a time - Just in time for one cylinder but not the next? So what happens to the fuel? Does some just sit there in a puddle waiting for next valve to open? Or maybe engine heat vaporizes most of it ? Kind of crude compared with modern direct injection but better than a carb, I guess. Anyone got a video

Anyway, my guess is that spray pattern is likely more important on diesels, direct injection and probably CIS.