924Board.org

[Legitimate Salvage]

Since there have been a couple of WUR threads here recently, I'd like to join in (and vent).

1979 924 NA

Finally got a fuel pressure gauge and hooked it up...

Round 1 (all values in PSI)
System Pressure = 64
Control Pressure cold = 62
Control Pressure warm = 64
Residual Pressure = 32 (20 minutes)

System Pressure is about 11 psi low.

Research (and questions at the KJet FB page) led me to believe there was a blockage at the WUR intake. So I got a pick and pulled out the screen (and put in a basket filter as suggested by Grey Goose on youtube).

Round 2
SP = 64
CPc = 40
CPw = 44
RP = didn't check

So there was some improvement in the control pressures, but now I had a new wrinkle. She wouldn't idle. She would start fine then rpm would drop until it just quit. I could hold the throttle and she ran just fine.

After sitting on it for a couple of days, I decided to pull the system pressure valve and check the condition of the little black o-ring at the tip. It was soft and no splits or cracks. It was a bit deformed, so I took it off and turned it around. There was only one shim disc behind the spring.

Also found that the banjo bolts on the fuel lines going to the injectors weren't all tight. One was only finger tight. Two came loose with very little effort. Only one "cracked" open like I would expect. Since I was in this far, I decided to pull the basket filters from the injector lines. Two were nearly completely bucked. One was crushed (and a smaller size than the others). Only one was clean enough to see the mesh weave. So I replaced all of the basket filters.

I put her back together and hooked up the pressure gauge.

Round 3
SP = 62
CPc = 31
CPw = 31
Residual = 23 (after 30 min)

Now, she would idle... barely. Maybe 300 rpm (and she loped like a straight 6 with a really hot cam). So I backed out the idle screw on top of the throttle body until I got to about 500 rpm.

Here's maybe where I got dumb: I got out my 3mm hex and adjusted the fuel mixture. 1/2 turn counter clockwise. I went a full turn in each direction, but at 1/2 ccw the idle smoothed out and came up to just shy of 1000 rpm.

My unscientific nose-in-the-tailpipe sniff test didn't detect that she was running too rich.

Hmmmm... let's go for a drive.

Throttle response was improved. Here to fore she's always felt like she was being restrained, now she felt more free if you get my meaning. She also had a wicked sympathetic vibration between 3200 and 3600 rpm that was much less noticeable.

Coming up to a stop, she would idle at 1200 rpm, but over 10 seconds or so it would settle down to 950. She's always idled at 1100 ish rpm... sometimes 1200, sometimes 800. Now the idle was at least consistently predictable.

Let's turn on the AC... no appreciable difference in the idle (maybe 100 or so rpm less). Previously idle would drop to about 700.

So, I've arrived at two conclusions (and courses of action):

1) My WUR is knackered. Control pressure is very nearly the same cold and warm.
a) I need to check the resistance value of the metallic strip and
b) confirm the voltage being fed to it.

2) System Pressure is low.
a) need to replace the o ring in the system pressure contol valve, and
b) shim the spring to see if I can get the system pressure up.

NOW FOR THE RANT...

The PO bought this 924 from the estate of the original owner. It had been sitting in storage for about 20 years in California. PO has a local "Porsche Specialist" get it running. Looking at the receipts of the work, it claims the fuel distributor was replaced ($866 for the part). There is no way on God's Green Earth that fuel distributor was a properly rebuilt unit. The mismatched/clogged injector line filters and the mushroomed o-ring tell me so. Zero work was done on the WUR (outside of running a can of seafoam through the fuel system). I don't know how this "specialist" managed to get this car running.
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1979 924 NA - AKA the Mid-life Crisis
2012 Audi A3 - The Daily
1991 MB 300D
1984 MB 300D
1966 Mustang I6

[gml]

That's wild, I'd be livid if I paid $866 for a new FD, a "Porsche specialist" tune up, and the system wasn't tuned perfectly afterwards, let alone the messed up o-rings and bolts. Another point in the books for "if you want it done right, do it yourself" I guess.

Your warm control pressure issue sounds odd; based on my understanding it makes sense that the bimetal strip isn't bending properly. But its not strictly necessary for the heater to be working to see warm control pressure, if you have the engine running and let it get warm, that should have the same effect of bending the bimetal strip as the heating element. In any case, missingparts.de sells refurbished WUR strips for a very reasonable price in case you identify the strip is at fault.

My issue is that cold control pressure is very low and it doesn't increase when warm. Maybe adjusting the height of the strip mount will fix it by moving it where the range of motion of the strip can let up on the spring, but it seems quite possible that won't work and I'll be in the same boat as you with warm control pressure doesn't rise.

I think your low system pressure could also point to a blockage in the fuel line leading up to the distributor. Maybe a new fuel filter is in order.
_________________
George

1982 924 NA 5-speed

[Beartooth]

Sounds like progress. The cold control pressure sounds a bit high (should be around 25 PSI at 70 degrees, according to Haynes). The warm control pressure should be a lot higher - 3.6 bar, around 50 PSI. I'd definitely check whether the heating element in the WUR is working and receiving power. The system pressure is a bit low, but I'd think would be close enough if the rest of the system was sound (70 PSI is the target pressure). A new fuel pressure regulator would include new o-rings and adjustment shims, or you could scrounge those. I managed to get my FPR to work ok with some new o-rings (actually came with the FD rebuild kit). As long as the FD is somewhat doing its job, you should be able to get a car to idle no matter how messed up the WUR and such is, but it'll bog as soon as you try to rev it, and won't be driveable until the fuel pressure issues are addressed.

The electrical connector on the WUR is the first thing I'd check - it should be around 20 ohms. If that's fine, then you'd have to see if it's getting power; you could also hot-wire it and see if that brings the warm control pressure into range and makes it run right. I think it'll probably run and drive even if that's not working, but it'll be crazy rich. On the "Porsche specialist," I have to wonder whether it's incompetence, or graft to blame. Any shop that specializes in classic Porsches would know k-jet and know to attack the system pressures before anything else. $866 isn't a shocking price for a brand new or quality rebuilt FD, but I have to wonder if the "specialist" rebuilt it themselves (poorly) and billed a new replacement price. I'd say that kind of thing is the worst part about k-jet: mechanics who really know how to work on them and can fix anything are hard to find, and many owners pay good money to have someone fiddle and throw parts at it with poor and frustrating results. I rebuilt my FD and it's been working great, and I could do one in a few hours now; maybe I need to go into business...

Anyway, one last thing to check is the fuel injectors. You can get some idea of where they're at, and clean them out a bit, by taking them out, dripping some sea-foam or Techron in the inlet, and then blowing them out with compressed air (start with the regulator around 50 PSI; I don't think you're likely to hurt the, but a shot at 90+ PSI can't be good). If you don't get some kind of atomization, they may need to be replaced. A better test is to hook them up and put them in small jars, hot-wire the fuel pumps (I put a jumper in place of the fuel pressure relay with the battery disconnected, then just put the negative terminal on loosely so I can easily turn it off again). Mine were well on the iffy side to start, but it seems to run ok, and they may have cleared up after plenty of fuel and fuel system cleaning run through them.
_________________
1980 931 diamond in the rough

[morghen]

With nearly 1k spent and the car not running properly, and likely another similar amount to get it running, plus the time spent and brain cells murdered, a certain EFI kit conversion is a good alternative

Regarding the wur, unless you’re both lucky and knowledgeable, you need a bench and the knowhow in order to calibrate the wur, and even then, its not guaranteed that the car will run perfect.
_________________
Supercharger and EFI kits
https://www.the924.com

[Riggard]

Your conclusions seem valid. If I were you I'd open the WUR and see what you find inside, sometimes the wire comes loose from the heating element.

Regardless, your cold pressure seems to be a bit on the high side.

btw, did you take the warm pressures after your test drive? Because if the strip is bad, the element will still heat up from the engine heat after a test drive.

[Legitimate Salvage]

Here's some of what I didn't put in my OP.

1. fuel filter is brand new with less than 100 miles on it (replaced in April of this year).

2. Warm temps (rounds 2 and 3) were taken after the car had been running and the temp gauge was just above 1/2 (I waited for the radiator fan to kick in the first time).

3. Fuel injectors were allegedly replaced by the PO when the "specialist" was getting her up and running. I've also run a 20oz bottle of techron through the system three times now. Not saying they aren't part of the problem, but the car starts, runs and drives (so I've moved them down on the checklist).

So far, the only money I've spent on the fuel system was for the fuel filter and the 3 bottles of techron... so less than $100 (and the testing gauge if you want to be technical).

Now I am considering buying a refurbed and bench tested WUR. So that would be about $500-600. I'd rebuild it myself BUT in all of the rebuild threads I've run across (Porsche, Mercedes and Volvo boards included), it seems that about half the time the WUR rebuild fails or provides less than satisfactory results.

I'm also considering a digital WUR, the unwired UTCIS-V to be exact. It's about the same price as a properly refurbed unit.

And YES one of Morghen's kits would solve all of this BUT, I'm not sure I'm going to keep this car. I like it, I enjoy it, it's great fun. However, deep, down I've come to terms with the fact I really want a mid '80's Mercedes R107 / 560SL. If I were dead set on keeping my 924, I'd be more inclined to go full EFI.

I'm going to check the resistance of the WUR and the supply voltage this afternoon. I'll report back.
_________________
1979 924 NA - AKA the Mid-life Crisis
2012 Audi A3 - The Daily
1991 MB 300D
1984 MB 300D
1966 Mustang I6

[morghen]

Before making the EFI kit i bought a UT-CIS unit.
While tech support was good, i was never able to make it work on my 924.
Might be something particular to the 924.

If you put an efi kit on a 924 its value goes up because it actually works , also you’re likely to enjoy it more..for the same reason.
_________________
Supercharger and EFI kits
https://www.the924.com

[Raize]

Considering the Mercedes you want is also k-jet, you can consider this a bit of practice…

[Riggard]

In all honesty, I dont really see how you can make a WUR Rebuild fail.

Rebuilt 2 and both succeeded. I think the main challenge is in getting the pressures right, most people seem to only touch the cold pressure/make that adjustable using the pin/bolt method. But other than that, it's really straightforward technology.

[Legitimate Salvage]

[Legitimate Salvage]

Well I bit the bullet on a UTCIS-V. I also installed a couple of shims in the System Pressure regulator (that got my System pressure up to 73 PSI... close enough for government work, imo).

My cold and warm start problems seem to be gone. The car, when cold, will idle at about 600 rpm. It's a rough/lumpy idle. The initial drive test (by the seat of my pants) shows much improved acceleration at low (around town) speeds. The car no longer feels like it's fighting itself to get moving. At WOT on country roads it's peppier and doesn't feel like it's straining. I know these cars aren't fast but it's much more responsive now.

For the first time since I've owned the car, the idle (when warmed up) holds steady around 1000 rpm. Enough so that I could actually see the timing marks on the flywheel. Before now, the timing mark was jumping around so much I couldn't really tell. With the vacuum attached to the distributor, the "0" mark was at TDC. I was tired at that point and didn't go any further with timing checks. That's next on the list.

The problems that still remain are:

1) The initial low/rough idle on cold start.
2) It still wants to idle high (1300 rpm) when I come to a stop. Give it 10 - 15 seconds and it will settle down to just over 1000 rpm.
3) Idle at times, can be a bit lumpy.

I've not messed with the AAV. I'm going to pull that next and give it the "freezer" test.

I'm also going to pull the spark plugs. I may just go ahead and replace them to eliminate that variable.

In all, I'm happy with the UTCIS-V so far.
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1979 924 NA - AKA the Mid-life Crisis
2012 Audi A3 - The Daily
1991 MB 300D
1984 MB 300D
1966 Mustang I6

[924RACR]

I'm sorta thinking some more ignition work might be in order, if you've got a lumpy idle.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Mclaren924]

Spark plugs foul out quickly in these cars especially when trying to revive an old beast that's been sat a while and/or has been touched and meddled with by PO's. Trying to get it running you subject it to not ideal running/cranking situations and this expedites the plug failure. They are so cheap it's really a no brainer unless you have done them very recently.
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1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold
1977 924 Slicktop "Pennie"-Most likely parts
1979 3/5 gt clone 924- Shop Test Car

[Legitimate Salvage]

[924RACR]

Oh, yeah, that doesn't sound ideal - because vacuum leaks.

Cheap/easy enough to replace and rule that out.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype