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*nod* Thank you for that. I think I left the parking brake on once, (everything triggers the !!! alert, even "I am lonely" and I missed it) so I probably need to re-adjust. I took a look around and it's the same star thingie as the 944S, so I'll do that when I get back from Vegas in a week (conference).
Meantime car is running pretty good. Still has the thunder problem when powering up, I'm still planning to replace the spark plug drivers (which I think are just big FETs that gate the logic signal from the DME between the coil and +12v to provide the energy build up for plugs. Kind of like points, and as such they do have a finite lifetime).
Now that I think about it I need to re-review the location of the check valve: If I have it right after the brake booster then how would the engine and transmission know I'm running at less than idle (as I go to WOT pressure wouldn't drop). Maybe the check valve is only supposed to be on the heater lines and flaps, not the transmission and fuel rail components.
Interesting. Is all the vacuum being picked up straight from the manifold and not from the brake booster?
Hm. Maybe I need to re-check all of them. In the meantime I went through the large pile of receipts and service orders, looks like a lot of good stuff was done:
Full timing belt service including water pump and all things and tensioner rebuild at 70k or so.
CV joints replaced
Window motors replaced, oddly enough the side mirror motors were replaced
A number of repairs to the tail light, I got that error again even though I checked all bulbs good. Does it use a photo-diode to cross-check the bulbs or current sensors?
2k rebuild of a lot of motor stuff towards the end, new coils, distributor caps, spark plugs, etc. That explains why everything looked refreshed. I think they also did some work on the vacuum lines as they look v. good.
Lot of other small to medium stuff.
Also some notes about how the lug nuts were so tight they broke off several in the rotors and had to drill them out. Hubs were tapped and ok, and new ones were installed at proper torque with anti-seize. Will be interesting to see if I can get them off now.
At least I feel comfortable running the engine up now to full power, will replace the spark computers when I get back along with a full brake job and check of the ABS systems. Then the car should be ready for MD inspection and plates!
Also looked at the codes, it has the Prussian Blue option paint metallic, how do I keep it from ever peeling like my other car did? Did they still use good paints in 1986 (1987 was a disaster IMO)?
The brake booster is supplied vacuum by the venturi (#17) and port on the right hand plenum. I don't specifically remember what comes off the little port on the brake booster check valve.
My 86.5 has the small check valve right off the port on the booster check valve, then to a 3-way splitter.
I will try to look in the morning where that goes.
Most other vacuum funtions are taken off the throttle body, either directly or through the 7-way splitter at the rear.
Ok. Mine went from the check valve to a 3 way splitter, one of which went to the vent controls at the firewall, the other went to another 3 way closer to the front of the car. There is a plastic line coming up from the passenger side firewall, I was guessing this was from the rear transmission, and it looked like it was being fed off this vacuum circuit. Someone had tied it to one of the hard lines there so it won't fall down, I'll try to take some pictures when I get back. But I don't remember seeing a 7 line splitter near the intake manifold rear section, will look again when I get back.
So I might be locked into a situation where the transmission now thinks I am a gentle grandma. Definite improvement for lower power driving, might not work optimally at higher speed.
And the idle is now stable as a rock. I need another 9248S to compare this one to. And a little Mit-e-vac since I am not using my AC vacuum pump and gauges on this stuff :-) ... Hm....
The plastic vacuum line for the transmission starts at the 7-way splitter then runs to the top of the bellhousing and on down. There it connects to a rubber line, then to the metal line.
You will need to remove the air box to see the plastic line to the transmission.
Check out these photos:
Plastic vacuum line comes from the 7-way splitter, then snakes under EVERYTHING and goes back.
Vac line goes under the TDC sensor.
From underneath, looking up, with the lower clutch cover removed. I know you have an automatic like I do, the lower aluminum cover is called a clutch cover.
As for the 7-way splitter, you will need to remove the MAF after the airbox. 7-way splitter sits under everything down in the Vee of the engine block.
You can just see the 7-way splitter peeking out from under the rear harness. Long handled needle nose pliers help manipulate this. And new curse words.
My 7-way splitter was hiding under those brown wires...I could barely see it without pushing them around.
The passenger side firewall vacuum line goes to the EZF ignition computer.
The HVAC flaps and such are all connected after the check valve that comes after the brake booster. I believe the splitter also sends a line to a reserve vacuum tank or something on the driver's side, not sure if there is anything else attached there. Certainly, the fuel, emissions, transmission etc all come straight from the manifold, most by way of the 7-way splitter.
I found recently that mine was all mis-routed. Somebody was just matching up ins and outs, and not correctly...
Ok, so there are two vacuum systems: One of the hotel circuits (heat, flaps, stuff like that) under the brake booster/brake fluid tank which is two Y connectors fed by the master check valve off the brake booster, and a second system run off the intake manifold running things like the shift system, fuel regulators, WOT/Idle mixture adjustments, and the like.
If so I should be able to gauge vacuum on the second circuit by pulling a line off one of the fuel rail dampers and checking for vacuum. Will see if I can do that before I roll out of town, otherwise I can fiddle with all this when I get back. Or just pay Ralph (the friendly MD mechanic) to do a walk through on the vacuum system.
But this car does move. I think I know which sensor is bad, driver's side front since before the antilock light comes on I can hear the chattering and feel a pulse in the driver's side front wheel. Another thing to check when I get back, not a biggie.
Big storm last night, good news is the car was dry inside this morning. So the outside seals are holding up well enough.
Noticed a rubbing sound in a hard parking lot turn, might need to look at the front end next. Still handles like a complete dream and the 928 engine sound turns heads......
Bulb control unit lamp controller....checks resistance to the taillights and throws warning. Very sensitive to bulb changes. Should be near passenger underdash tray at console.
Correct...you can do that, or you can do it from the vacuum line plugged into the EZF, depending on which is easiest. When going through my system, I was measuring off the brake booster and my vacuum was very good, but I still had leaks. That's when someone told me to check it at one of those locations, and sure enough...big difference.
Originally Posted by Christopher Zach
Ok, so there are two vacuum systems: One of the hotel circuits (heat, flaps, stuff like that) under the brake booster/brake fluid tank which is two Y connectors fed by the master check valve off the brake booster, and a second system run off the intake manifold running things like the shift system, fuel regulators, WOT/Idle mixture adjustments, and the like.
If so I should be able to gauge vacuum on the second circuit by pulling a line off one of the fuel rail dampers and checking for vacuum.
For the bulbs, ah ok. Probably an op amp triggered by not enough current across a sense resistor. Which could mean that I need to use bulbs with a higher current draw for the rear running lights (it onlu triggers when I turn on the head lights). I'll look up the OEM bulbs and try something that pulls a bit more current.
For the vacuum, got it, will test that when I get back. Thanks all!
Chris; email Roger at 928srus.com, order all the tail bulbs as a batch. Order any non illuminated bulbs in functional pairs and replace both right and left. Your tail bulb sockets are probably tired and the socket "cylinders" become a bit enlarged. This aggravates the lamp sensor circuit. The circumference of the cylinders can be restored by gentlly squeezing with pliers. Use De-Oxit when plugging bulbs in.
Be careful on replacing those ignition final drive amps. You may need ground point cleanup and spark plug wire ohm checks more than amp replacements. I threw away perfectly good 27 year old Bosch amps and replaced with after markets when peculiar problems emerged. If you indeed replace the amps, buy only Bosch!
Hard shifts = broken vacuum curcuit to the trans modulator. There are plenty of opportunities for rubber vacuum hose end piece chafing at either end.
Btw: the antilock brake wires fasteners tend to give way after a while and the wires can hang over rotating half shafts and such. Resecure those wires and clean the metal flakes off the sensor magnets (with the abundance of free time you have ;-) )
lastly for now; if your idle stabilization valve is as old as many of ours when we purchased our sharks, your air hose is likely cracked and deformed. Make sure that valve is responding properly and that your hose is not compromised. Good operation here will really help your idle
More on those final drive amps; the after market amps can be susceptible to electrical noise. The Bosch aren't. That creates peculiar on again/off again issues with non-Bosch.
Ok. I bought a set of used ones from a 928s to start with, will sit down and troubleshoot them when I get back. What's interesting is that they are the same part numbers as on the 944S, and the S has the added two knock sensors going right to the drive amps, not the DME.
Which makes me wonder if one could add knock sensors to an 86 928S. From what I remember the drive amps contain FETs to switch the 12v to the coils and also a time delay to allow timing changes based on inputs from the knock sensors. If that is using a set of op-amps then those could go out of whack and produce intermittent "change the timing dude" messages which can result in the usual havoc.
Might just order a new set while I am out here in Vegas just to be sure. The plug wires were replaced relatively recently, my guess is a lot of the clean up work was an attempt to find this problem. But the amps are original, no one thinks to look at them. (Believe me I spent 2 years hunting this down on the 944S. I literally even replaced the whole fuse box thinking there was noise there. Idle valve, injectors, 3 DMEs, knock sensors, complete vacuum job, intake boot, I even pulled the exhaust manifold and replaced the copper rings thinking it was air being ingested. Replaced spark computer, problem gone for 80k miles. UG!)
Just replace the heater valve with the correct modern version. Even if the vac will hold the valve shut, the flap plate inside deteriorates and passes hot water, even in the fully closed mode. In summer, I just put a big marble in the hose line to the heater and make sure it will never, ever flow water. Then, take it out in Oct and viola - heat.
I had an 86 and the fuse and wiring for the AC fan would never stay working. I did a u-make-it from the jump post, through a relay, and then an inline 25A fuse to the fan. Picked the trigger for the load relay from the AC compressor line, so anytime the AC was running, the fan was on. Not a recommendation, but I got tired of fighting the embedded wiring and just started over.
07-23-2017, 04:51 PM
