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'73 450SE - should I replace intake manifold seals?
Before I get into replacing the air intake manifold gaskets and plenum
seals, is there anything I have missed? Apologies in advance for the long posting - wanted to give a fairly complete run-down of what I've tried. I'm not an auto mechanic or engineer, and am fairly new to this, but am keen to learn, and have been reading a lot about D-Jet. My 1973 450SE is running smoothly, but only pulls 10 mmHg vacuum - measured near the take-off for the central locking and heater (before the vacuum check valve). The car is running very rich - black smoke from the exhaust at idle, and exhaust smells of gasoline. I got this car from elderly friends who couldn't maintain it well. It had been serviced at a non-MB shop for many years. I found several leaking rubber hoses under the hood - now replaced. Timing is now set to 4-5 degrees ATDC. Points are OK, and gapped to specifications. Transistorized ignition trigger points are cleaned. Idle is to spec: ~750 rpm when warm. Dwell is to spec: 31.7 degrees. Injectors pulled and reconditioned last week - two were leaking badly. Now no leaks, good flow. Injector seals and gaskets replaced. Rubber line to MAP sensor replaced. Rubber "Y" between AAV and throttle body replaced. All rubber connectors between hard vacuum lines to distributor body replaced. PCV hose replaced. AAV cleaned with carb cleaner. ECU is set to 6 clicks from the right. Leak down test shows all cylinders within specifications for test. Resistance on air-temp and water temp sensors are to spec. New air filter. New spark plugs (spark plug cables are fairly new - last few years). New distributor cap and rotor. Did find another fuel pressure leak - apart from previously leaking injectors. Seems to be the ball valve on the return to the fuel pump - followed the testing method in the service manual. I know the central locking has a leak, so this has been plugged off. So... have I missed anything? Should I check anything else before I attempt to renew the air intake manifold gaskets and plenum seals? I understand this is a two day job for someone with experience, and not to be undertaken lightly. I was hoping to avoid! Thanks, Joe |
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Vacuum leaks at the intake manifold seals may have your engine run lean at idle, not rich. And if your idle is at 750 rpm, it must not be that bad. Does the engine stall when you screw the idle air adjustment all the way down?
I would test the MAP sensor: the pressure port should hold a vacuum of about 15 to 20" Hg vacuum with no leakage. Resistances should be about 90ohms between pins 7 and 15. And 350ohms between pins 8 and 10. I would also look at if anybody has fiddled with the MAP sensor adjustment. |
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Rich idle can be a misadjusted throttle position sensor. Your ECU thinks the engine is pulling a low-speed load vs just running. Check to see if that's the case. Moving the ECU screw would have no affect on idle mix if this is the case. Turning the ECU screw to the right does richen the mixture. It's the opposite of the MAP.
I would say, if the MAP is not the source of the vac leak, your seals do need replenishing.
__________________
Current: 2021 Charger Scat Pack Widebody "Sinabee" 2018 Durango R/T Previous: 1972 280SE 4.5 2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi" 1999 Chrysler 300M - RIP @ 221k |
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Regarding the TPS. I have attached the pdf I put together when I checked mine. Most important thing is to get the idle switch to signal to ECU that throttle is closed. Have you checked vacuum at distributor? Sometimes the pin hole near the throttle plate is plugged and the vacuum retard is not working. Also check that your distributor centrifugal advance is working. You should see timing go up to about 25-30 BTDC as you increase speed to 3000rpm. Even with cleaning, the AAV can stick. Try squeezing the elbow hose and see if it affects the vacuum reading once you have the timing set. How do the plugs look after running. They should be a golden brown colour. On my car, I had sooted up plugs and intake manifold. Problem turned out to be trigger points. Although they tested out using method in manual, they were staying closed for too long and causing problems with fuel injection. Basically the fiber cam followers ahd worn out. I had aspare set and that solved the problem (see separate thread on adjusting trigger points) Regarding checking MPS and all other components, it sounds like you must have documentation. If not, I have a check list that I found on line that I use. Finally, you must beg, buy, steal or borrow a good exhaust analyzer in order to adjust the MPS and ECU. Once you have one, I can send you the methods for adjustment and specs I was given by several expert MB mechanics.
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Graham 85 300D,72 350SL, 98 E320, Outback 2.5 Last edited by Graham; 11-05-2009 at 11:27 AM. |
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Many thanks to GGR, Tomguy and Graham for their very helpful comments.
I had to wait until today to get some time to work on the car. Here is my progress report... 1. Air idle valve - when screwed all the way in, the engine slows, but does not stall. 2. MAP Sensor Holds at least 20" vacuum. This dropped to 17" after 4 minutes, but I hadn't hose-clamped the connection to the MityVac. Resistance between terminals 7 & 15 = 91.5 Ohms Resistance between terminals 8 & 10 = 331 Ohms More below 3. Timing At idle, with vacuum connected at distributor, timing is 5 degrees ATDC. At idle, with vacuum disconected from distributor (and plugged), timing is 10 degrees BTDC (just to be sure I am not reading the dial incorrectly, the pointer was indicating to the LEFT of the zero mark with vacuum connected, and to the RIGHT of the zero mark with vacuum disconnected & plugged). Vacuum measured at the distributor (using vacuum line disconnected from distributor), is 15" Hg (therefore 10 degrees BTDC). Vacuum measured at the line coming from the manifold, to connect to central locking = 10" Hg. 4. TPS I did not have time today to dismantle the TPS and service it as described, but I did try a couple of tests. With ignition set to "on" but engine not running, I was able to move the throttle manually from closed to fully open, and counted 20 clicks as the injectors cycled. I attempted the test where voltage is measured at terminal 17 of the TPS connector, and a 0.016 in feeler placed between the throttle stop and the the throttle. I couldn't get the test to work - there is supposed to be voltage (with ignition on) when the feeler guage is in position, and no voltage without the feeler guage. I couldn't get any voltage at any time. I assumed that I had to "piggy-back" onto terminal 17, and compare with car ground. Is this correct? 5. A question about MAP adjustment I had a close look at my MAP sensor today. I have read in several places that there is a hex screw that is to be adjusted (1/8th turn at a time). I cannot see any hex screw on my MAP sensor. When looking at the end opposite the electrical connector and sensing port, there is a hole where the "epoxy covered Full-load Stop Screw" (Paul Anders' web-site http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm) should be positioned. This has been removed, which I understand was often done. However, I seem to have a clean cylinder there, with a small cylindrical hole at the bottom. I can't see anywhere to make any adjustment with a hex key, should this be needed. Has something "crazy" been done to this MAP sensor? I tried to snap a picture, but it is quite difficult to get a shot of the interior of the screw hole. Joe |
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10 deg BTDC is a lot of advancement - I don't think I could even get that. Slacken the distrib bolt and rotate back a few degrees while watching vacuum. You may find best vac with slightly less advance. Quote:
In other words, when you take your foot off pedal, the resistance should be zero and all other times infinity. Quote:
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Graham 85 300D,72 350SL, 98 E320, Outback 2.5 |
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Thanks Graham! Here's the progress - not much today...
Vacuum measured at the manifold - short rubber tube at rear of engine on passenger side - before vacuum check valve on firewall - still only 10" Hg. I need to get in there and make sure the orifice is not blocked - I am pulling 15" at the distributor (but that is with different timing, because the vacuum advance is removed when I measure at distributor). Will have to play with timing, as suggested, but see below. TPS Feeler gauge "out" : 3 Ohms Feeler gauge "in" 0.016" : 0.3 Ohms Feeler gauge "in" 0.020" : 3 Ohms Feeler gauge "in: 0.025" : open circuit I figured this might be close enough (0.025" vs 0.016"). What do you think? I couldn't "play" with the timing today. If you can believe it, the only 5mm Allen key that I have that is long enough to reach the distributor lock nut is not here! I have to buy another one this week. I tried a "test"... I disconnected the vacuum line from the MAP sensor, and blocked the line from the manifold. I then pumped 18" Hg at the MAP sensor with the MityVac. Vacuum held. Then I started the car. It ran about the same - idles smoothly, but lots of black/grey smoke. MAP Sensor I look again - even unscrewed the MAP sensor from the fender for a perfect view. I see no sign of a 4 mm hole for an Allen key! There is a circle of resin, surrounding a cylinder with a thread on the outside, which is quite smooth on the inside. This may be the outer screw (looking at Paul Anders' website photos). But htis is at the level of the surface of the MAP body. At the bottom of the inside of the cylinder, is a small (1.5 - 2 mm) smooth hole. I see nowhere for a 4 mm Allen key. In particular, I see no "inner screw" - no visible line for a screw driver to make contact with. I am getting suspicious that something may have been done to the MAP sensor. I have tried to take a meaningful photo, but the screw is small, and hard to get a clear image of. I will try with a better camera later. Will keep reporting as I make progress. Thanks again for the help, Joe Last edited by a5a1234; 11-08-2009 at 08:13 PM. |
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I would try measuring on the line to the MPS. I used a 5/16" Tee that happened to fit into the end of that hose, plus a short piece of 5/16 hose onto MPS. But that location at back of engine should work. The hose comes off a connection that is also hard piped to the transmission I suppose it is possible that either the rubber hose is leaking or whatever that transmission line connects to is leaking (modulator?) Quote:
The important things are: - throttle plate IS closed when linkage lever is against the stop ( I had to adjust the stop to get this to happen). - switch is closed in this position (12-17 - zero resistance) The manual says 0.4MM or 1 deg is "slightly open"). I would imagine 0.025" is good! But do check that the plate is fully closing. Quote:
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Hope you are having fun. I have been through same process a couple of times! Too bad Vancouver and Kingston weren't a bit closer!
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Graham 85 300D,72 350SL, 98 E320, Outback 2.5 |
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The 4.5's MAPs are different than the 3.5's - the 3.5 MAP is a slotted screw and the 4.5's is like that picture, with a hex head screw. The 4.5's gets stripped out internally if you much with it too much (ask me how I know). So if you can't locate said screw this may be why. Keep in mind yours may be covered with a black cap.
With your engine running, try to spray carb cleaner around your injectors and your manifold seals. If your engine slows/stalls, you need new seals and this is why you're running so rich with such low vacuum.
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Current: 2021 Charger Scat Pack Widebody "Sinabee" 2018 Durango R/T Previous: 1972 280SE 4.5 2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi" 1999 Chrysler 300M - RIP @ 221k |
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Thanks Graham, Tomguy. Having your help in this is fantastic!
I have attached a (poor) quality picture showing my MAP sensor with a 4 mm Allen key in the screw. The Allen key does not make contact with the interior sides of the screw, which may mean that it has been stripped, as Tomguy suggests! Hopefully you can see enough detail. Mine definitely does not have any hex shape to the inside! The Allen key is pushed in as far as it will go. Throttle plate looks to be completely closed at idle. It is not horizonatal, but it looks shut. I found a leak in the transmission modulator. That must the reason why the vacuum measures lower at this take-off. I will get a 5/16th" Tee to measure vacuum at the MAP (I had only a smaller diameter Tee available today). A transmission modulator leak shouldn't be too "large" should it? I have read about people driving around with leaking modulators, and waiting to "get around" to replacing them, so I assumed this would not be a critical thing. I have some propane available. Should I try that around the injector seals and intake seals? It would be easier to snake that around with some hose, than try to get carb cleaner close to the intake seals. Yes, I am having fun, but I hope that eventually I'll get this car running properly. It ran well for the first few weeks that I had it, and it was great fun to drive :-) Last edited by a5a1234; 11-08-2009 at 10:42 PM. |
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But you should get the vacuum leaks fixed first. (BTW - I use a propane torch with hose attached, but you need to be careful about not opening it too much so that gas gets into the intake. Have you checked your fuel pressure? I have had fun adjusting my mixture by adjusting the fuel pressure. With the AFR gauge, it is easy to see the affect the fuel pressure has at idle and while driving. My car runs lean at 28psi and rich at 35 psi. This is less sensitive to adjustment than the MPS is. But, considering your MPS hex socket has been stripped, it does sound like your mixture problem could be there. Maybe you could get a slightly larger key to fit? Or maybe look for a used MPS.
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Graham 85 300D,72 350SL, 98 E320, Outback 2.5 |
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Thanks Graham.
I did the fuel system check two weeks ago. Pressure is 28 psi. Pressure wouldn't hold, so I carried on with the tests in the service manual, and found two leaking injectors (already mentioned). Had all injectors serviced - now no leaks, but it looks as if there is a problem with the ball-valve on the return to the fuel pump. I thought I'd leave that for the moment. I'll do the propane test tomorrow (evening) I hope. I want to check with the local equipment rental people to see if I can get an exhaust gas analyzer. I realize that I can't do any proper adjustments with out one. At present, it would be good just to get the car running without clouds of smoke! |
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What colour is the smoke? Even with very rich mixture, I have not seen clouds of smoke. Sometimes just a little soot. Could it be be coolant, oil or ATF causing the smoke? BTW - I was able to get local garage to run a provincial emission test on my old car as a "mechanic training run" - $35.00!
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Graham 85 300D,72 350SL, 98 E320, Outback 2.5 |
#14
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Torx bit - I think it's T25 - can go into the stripped MAP sensor screw. You may need to hammer it in but it'll then allow you to adjust it a FEW TIMES before it re-strips. The ultimate solution you need is a new MAP most likely. Although it really is a "Set it and forget it" once you have all your vac leaks sorted out with 100% confidence.
__________________
Current: 2021 Charger Scat Pack Widebody "Sinabee" 2018 Durango R/T Previous: 1972 280SE 4.5 2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi" 1999 Chrysler 300M - RIP @ 221k |
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I think I'll leave the MAP sensor alone for the moment - there are more things to be corrected first, it seems.
Timing I was able to adjust timing this evening. With vacuum line to distributor disconnected and blocked, I set timing to 8 degrees BTDC. Vacuum was measured at a Tee near the MAP sensor at 16" Hg (the best for ages). With vacuum line re-connected to distributor, timing was then about 8 degrees ATDC. Vacuum measured 14" Hg at the "Tee". Re-checked idle - 750-760 rpm (wanders about a bit). Re-checked dwell - 32.6 degrees I pulled two spark plugs to view. The first was from a cylinder where the injector has been working fine. The second was from a cylinder where the injector leaked (before reconditioning last week). Both plugs are very black and sooty. I have snapped two pictures - forgive the blurring, as I tried to get close enough to show the details. I hope these images are good enough to give an idea of how sooty the plugs are. Still blowing what looks like grey/dark smoke. I'll keep at it and report progress. |
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