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Will do. The parts I listed above are commonly available. The fitting is a 5/16" (or 8mm) barb to barb to 1/8" FPT pressure sender adapter tee. It's marketed as for fuel pressure purposes, but I don't see any problem with using a stainless steel adapter for coolant.
The pressure switch is some generic 2 PSI switch from eBay, but it looks like Stewart Warner makes one with screw terminals that might be a little more reliable. The Stewart-Warner part number is SW76061 and they sell it at Jeg's.
There are also some similar switches sold for use with spas, some of which are even adjustable. They claim to be "pneumatic" switches though, so I don't know if they'll hold up to ethylene glycol.
I'm not absolutely sure about that pressure rating. 2 PSI might get tripped too soon...
I also don't know if the original switch is normally open or closed. When you guys delete this switch, do you leave the wires disconnected or do you connect them to one another? If you connect them to one another, then this switch should do the trick.
It's only about $40 total, and a pretty easy install, so I'm going to order these and do the experiment. I'll let everyone know how it works out!
For the fans, at the bottom corner of the radiator is the temperature switch that turns on the fans. If you disconnect the two female spade terminals and jumper them together, that would make the fans run all the time. That will tell you if it's just the temp switch sensor that's bad or something with the fans themselves.
It took me forever to find that coolant temp switch in the radiator. I felt really stupid once I finally found it, but it sure is hidden!
I suspect it's "out of spec" because the resistance I measured on it is quite high. I won't be exploring that further until I know the Fan Amplifier works properly, though.
You're way more on top of things than I am but one of the things that jumped out at me with your stalling is that it sounds a lot like what was happening on my S4. I was really worried it was the LH, or some other electrical gremlin, but it seems to have been the fuel pressure regulator (or the dampers, I replaced them all).
Interesting! So, maybe under high vacuum coming down a hill with the throttle closed, the fuel pressure regulator(s) are doing something stupid?
What's the right way to hook up a fuel pressure gauge, anyway? I don't see a test port. Do I need some kind of Porsche-special test port adapter?
I don't see a test port. Do I need some kind of Porsche-special test port adapter?
It's also right in front of ya. Passenger side fuel rail, there's a big cap nut pointing towards the front of the car. Careful taking it off, it's holding a sealing ball within the cap that you don't want to drop. M12 x 1.5 thread.
It took me forever to find that coolant temp switch in the radiator. I felt really stupid once I finally found it, but it sure is hidden!
I suspect it's "out of spec" because the resistance I measured on it is quite high. I won't be exploring that further until I know the Fan Amplifier works properly, though.
Interesting! So, maybe under high vacuum coming down a hill with the throttle closed, the fuel pressure regulator(s) are doing something stupid?
What's the right way to hook up a fuel pressure gauge, anyway? I don't see a test port. Do I need some kind of Porsche-special test port adapter?
Depends WHY you think you need a FP gauge. A lot could be wrong before a bad pump is a possibility, it is not PWM controlled, they work or they dont. Partial throttle/etc wont change how it operates or how the car runs.
Well, I have a pressure gauge and fuel pressure is easy to confirm if there's a test port.
Here's what I'm working with so far:
- Spark is strong, and I just replaced all the plugs and wires. Engine runs infinitely better after a tune-up, but is far from "good". No sign of spark "leaks" anymore.
- No problems with hard starting, so pump, regulator, injectors are not leaking and losing pressure overnight.
- Misfire comes and goes at different RPM ranges, primarily 1500-2000 rpm, then 2750-3000. Runs nice and smooth at low RPMs.
- Transmission is still shifting a little hard. Replacing back section of cracked vacuum modulator hose helped a lot, but not 100%. Haven't yet checked out the front section.
So, I'm concluding that:
- (Mostly) ruling out spark problems
- Could possibly be a couple of crap injectors...but that doesn't seem likely:
-- I know none of them are leaking
-- If one was plugged up or not firing, I would expect a misfire that stayed consistent at all RPMs.
-- If one was partially plugged up or had a terrible spray pattern, I would expect a misfire that got consistently worse under higher load.
-- I might pull them and send them off to be cleaned & checked out, anyway.
- Could be a crank sensor- I've seen marginal ones with metal filings all over them that fail to pick up a signal under weirdly specific conditions, as the flywheel moves in/out under thrust load.
- Could be MAF sensor. I'm not sure how to test this correctly. I wish I could drive it with a recording voltmeter / tach attached and get good data.
- Could be a crap ground somewhere causing the LH to go senile.
- Could be the LH. I hope not!
Last edited by android606; 11-09-2022 at 08:11 PM.
I must have gotten lost in the long list of things you did and missed that you didn't mention the CPS. If it's original, it's probably pretty crispy at this point and in need of replacement. That might be worth a look.
Clogged injectors can have wildly variable responses over throttle range. From buckingblike a bronco to smooth, albeit lean, running. Coughing and driveline shock. Etc. I saved an 85 that sat for a long time. Waited far too long to address injectors. Blamed and chased everything else. Popped in a cheap set of design 3 bosch from 5.0 motorsports and it was night /day solve. Solved excessive temp also. Inside of headers were white from heat.
There used to be someone on the list who had a service rebuiding MAFs and brains. For me, as part of the service, he evaluated my parts first to see if they were ok. If it were me, I would tend to Witchhunter the injectors and send the other parts off to that guy before spending tons of time trying to figure out what's wrong. Also, I really like smoke testing for intake leaks. I often find things with a smoke test that I have missed visually. Inexpensive smoke test boxes on ebay.
Clogged injectors can have wildly variable responses over throttle range. From buckingblike a bronco to smooth, albeit lean, running. Coughing and driveline shock. Etc. I saved an 85 that sat for a long time. Waited far too long to address injectors. Blamed and chased everything else. Popped in a cheap set of design 3 bosch from 5.0 motorsports and it was night /day solve. Solved excessive temp also. Inside of headers were white from heat.
BTDT, my 88 S4 did this...but the cheapest set of ford 19s on Ebay fixed it right up.
There is, and the WSM procedure is to simply test volume out it over time.
But im 100% sure it's just fine..you dont have pressure related issues.
Haha okay, I'm convinced. I'll hold off on the fuel pressure/volume test.
The crank sensor looks like it's from the 1800's. A marginal crank sensor is untestable without an o'scope. A new aftermarket one is only $45, so I ordered one from Roger. I'll just swap that out and see what happens. It looks like it will be tons of fun to remove.
If that doesn't fix this misfire garbage, a new set of Ford injectors might be in my future.
Hey, I just thought I would give everyone an update. I took a hiatus from car projects to finish a basement earthquake retrofit I've been working on. (Psh, houses, who needs 'em??)
When I left you all a few months ago, I had limped the 928 across the country from Mass to Cali, running pretty rough, with no working fans, and a laundry list of problems.
Now that the weather has intermittently lightened up a bit, I've started at it again.
1) I replaced all of the center console switches in front of the shift lever. That got me:
A rear window wiper that works (but is clonky and loud).
A driver's side window that rolls up and down! Woo-hoo, I can use a drive-thru now!
A passenger side window that clicks a bit and acts like it wants to work, but doesn't.
A sunroof that opened and closed a half dozen times or so, just enough for me to clean and lubricate the tracks and blow the junk out of the drain tubes. Then, I closed it and it made a sort of "crack" sound. Now, it only seems to try to open on the driver's side about 1/2" or so, and gets stuck. It will open that far, and it will close. Something over on the passenger side broke- I guess I'll be taking the headliner out soon. Gotta have a working sunroof for summer!
2) I replaced the crank sensor. It looked easy to reach, but it was a severe pain to get in there and pull hard enough to get it out! I finally got it out with a really long pair of pliers with a 45-degree bend at the end, and a small block of wood to use as a fulcrum. That, plus some PB Blaster got it right out.
I was surprised, the bottom end of the sensor actually looked really good. Like, fresh out of the box good. It's like when you buy an old calculator or something and the previous owner never peeled the protective film off the screen, and you finally pull it off. I felt kind of stupid for removing it, and almost put it right back in. I'm glad I didn't.
The connector was a real pain in the *** to get at. Even with the air box and MAF sensor out of the way, it's buried under a bunch of other wires and crap. None of those things can be moved very much without removing the intake...no thanks. When I finally got my long pliers in there to pull the connector loose, it broke in half. The entire plastic end of the connector stayed plugged into the car's wiring harness, but all the wires with pins attached came off in my hand. I had to pry the remaining plastic out of the harness connector with a small seal pick, and it came out in small flakes and chunks.
The pins were very slightly green, but really not too bad considering what was plugged into them. I cleaned them up with a little 2000-grit sandpaper and a dab of deOxIt, and they looked like new. Even the plastic shell looked nice.
Installed the new sensor, fired it up...and it ran about 15% better. Noticeably better idle, noticeably smoother going around the block. Progress, for sure, but not a landslide victory!
3) While I had it out, I cleaned up the MAF sensor. It had a lot of salt spray corrosion crust all over it. I cleaned it up with a brush and a wire wheel and got it all shiny, then hit it with a spray of clear lacquer. Bling! Then, I polished up the inside with a small buffing wheel and some white compound, for a near-mirror finish. Definitely unnecessary, but it made me feel better. Cleaned up the wire and sensor assembly, and the connector, with some electrical cleaner.
4) I still had a really bad lopey misfire problem that kicked in at about 2000 RPM. A really bad one. The fuel injectors looked pretty ancient, so I pulled them out. Injector Mass Grave
The pintle caps and o-rings look brand new, though. Hmm. I guess the mechanic in Mass pulled them out when he had the intake apart, and put new caps on them? There's no way those caps have 34 years and 100,000 miles on them.
I cleaned up and de-rusted the fuel rails, and gave them a paint job. Put it all back together, bled the fuel rails, fired it up...
...and it ROARED to life! Night and day! I took it for a test drive and it was like driving a real sports car! No misfire, just pure awesomeness! I only meant to take it around the block, but instead of turning left, I continued on away fro home. I took it down a country road and up the freeway, down another back road, and even got it sideways a couple times! My test around the block turned into an hour long joyride!
Then it started, very gradually, sputtering and running rougher. I could tell this was the same thing it did in Nevada or Colorado or wherever that was- Not the same lopey misfire, but an intermittent refusal to fire at all, for just a few seconds at a time. Especially likely to happen going downhill under very light throttle. I drove it for a couple of days, and the problem gradually happened more often and for longer periods of time. Now, it's constant. Whatever beast is causing it got poked and angered when I replaced the fuel injectors.
It no longer wants to idle. The idle control valve is opening and closing, idle speed surging up and down until it dies. Keeping the throttle open a bit and keeping the RPMs around 1000 will usually keep it running. Giving it just a little tiny bit more throttle will cause it to die. When it tries to die, giving it full throttle will usually (but not always) cause it to sputter back to barely-living, and you can then carefully keep it at ~1000 RPM again.
I haven't diagnosed it any further, but here are my thoughts:
Maybe my spirited joyride sent an almost-dead coil to the nursing home, and it's sitting a rocking chair waiting for some applesauce?
A cylinder suddenly properly firing would cause the O2 sensor to read lean, which would cause the ECU to richen up the entire bank of injectors. Maybe a longer duty-cycle is straining the output driver on the ECU? I wish I had a scope!
Before I took the injectors out, I blasted the area around them with air. That didn't do anything to the thick layer of oily dirt, so I sprayed it with Purple Power, let it soak for a bit, hosed it out with the garden hose, and then dried it all out again with air. Maybe that got water into a connector somewhere? It seems unlikely since it ran well for a while, but maybe? What does this engine do if the throttle position switch is disconnected? I think that's the only connector I couldn't get at to check for water.
Providing more fuel to a full set of working injectors might be straining a dying fuel pump?
I still haven't gotten to the electrical connections in the passenger side footwell. Could be anything going on in there.
Throttle position sensor needs to click when the pedal is just pressed a bit from it's resting position. What you describe sounds like it could be throttle position sensor related. Finally driving it now could have also taken any junk that was in the gas tank and gummed up the fuel pump or clogged the fuel filter, especially if the in-tank strainer has deteriorated and is no longer filtering junk in the tank from making it to the pump.
I tested the TPS by checking continuity at the LH connector. It seems to be working perfectly: Pins 2 & 5, continuous when throttle fully released. Pins 3 & 5, continuous when throttle fully depressed. Neither continuous when throttle is in the middle somewhere.
I'm with ya on the junk in the gas tank theory: I had an old boat with a carbureted V8, with some pretty similar symptoms. It took me months to figure out the cause of the problem- turned out to be a small piece of a dried up leaf that got sucked up the fuel pickup and was lodged in a 90-degree elbow. Sometimes, the leaf chunk would suck up at high throttle, and the fuel flow would wedge it against a small ridge in a brass elbow and cut off the fuel flow. The engine would sputter and cough and die, and leave me floating down the river. Then, sometimes immediately, or sometimes after lots of cussing and taking things apart, the leaf bit would dislodge and sink back down the fuel line at some low resting point and it would fire back up like nothing ever happened. Buzz around for three days or 15 minutes, and it would sputter and cough and die again.
Every time I had it back home in the driveway, it would run great, and the fuel flow would check out just fine.
One day, I pulled out the whole fuel line including all the fittings and everything, from the pump back. I shot a bunch of carb cleaner in it, and blew it out with the air compressor. Leaf bit came flying out of the fuel pickup tube and flipped me off on the way out. I put it all back together and never had any more problems. That damned leaf cost me a good $1000 in parts, dozens of hours, and a lot of ruined boating days!
Time to check out everything from the fuel tank forward...
I pulled out the fuel level sender and shined a flashlight around inside the tank. There's a good amount of general filth and some sparkly metal flaky bits in the bottom of the tank, but the pickup screen is intact and looking pretty good.
I then pulled off the fuel pump. The nut was torqued down tight as heck onto the banjo fitting on the output end of the pump, but it wasn't even finger tight below that, where the fitting screws into the body of the pump. D'oh. Maybe it was pulling in some air? I don't know, but it's a miracle it wasn't leaking like a sieve.
I also pulled off the fuel filter. There's a sticker on it that says "Purolator 11/90". I'm pretty sure that means the fuel filter was manufactured in 1990. Oof. When I took the fitting loose, I drained it into a jar. The fuel that came out - of the OUTPUT end - looked opaque and brown like chocolate milk, with sparkly metal flakes in it.
I ordered a new filter, expect to get it tomorrow. Where are all those metal flakes coming from? Maybe from the fuel pump? That's the only real moving part in the path of the fuel, right?
11-02-2022, 04:29 PM
Friendly progress update
