928 questions

jarroyo · 07:03 AM

while trying to get my car running finally I ran into a few problems and have some questions. If anyone can supply answers it would be greatly appreciated. The list of probs is as follows.......

1: fuel pump was bad and a new OEM one is $350 so I'm goin to go the aftermarket route. so what is the typical fuel pressure rating for this car?

2: I'm worried about water pump failure causing major valvetrain dammage. Is there anyway to tell if my water pump is good or on it's way out the door? I only ask this because I heard that 928's are notorious for water pump failure. Are there any warning signs or does this happen suddenly?

Any advice will help since I know nothing about this car! Also I've looked all over and cannot find a service manual for the car. Does bentley make one?

BTW the car is an 81, heres a pic of the engine I don't know exactly what motor I have in it.

928ram · 05-08-2005, 09:04 AM

Pelican Parts (link at top of forum) lists the fuel pump for $209.45, there are aftermarket available but the price is about the same and you'll need asst. adapters to get it fit right. Go with OEM (Porsche PN# 928.608.104.01; Bosch PN# 0580.464.017[also Pelican Parts #])
I think the pressure is in the 40-60 psi range.

It's the timing belt failure that will hurt the valve train on some engines; your's appears to be the standard '81 US model, which won't suffer valve/piston contact on a belt failure.

Water pump failure is normally seals leaking, there is a rare incident of the impeller coming apart and damaging the block, but that's very uncommon. Most folks replace the water pump when they do the belt because the tension of the new belt can cause the seals to leak and it's such an involved job to replace.

I've replaced the belt on both my cars without replacing the pump and had no problems with the pump leaking. Your call.

See my reply in the "79 928 power mirror control" thread about the service manuals.

jarroyo · 05-08-2005, 05:49 PM

thanks alot 928ram for the info, one more question if you will, I got the car to fire up today and then ended up with it not firing at all now, seems like I have no spark! I checked across the terminals on the coil and only got a reading of 5.43 volts. my battery still has a full charge, what would cause this? the coil is new, and so is the battery.

928ram · 05-09-2005, 09:36 AM

The coil doesn't run at battery voltage, the are 2 ballast resistors which pull the run voltage down (6V sounds right). The ballast resistors are the white ceramic and metal devises just forward of the P/S pump resevior. One of the resistors should be .35-.45 Ohm, the other .55-.65 Ohm. I believe the ohm ratings are marked on the resistors.

The "green wire" which feeds the signal from the distributor to the ignition control box has been know to give no-spark problems; I've never faced this but I hear it can get loose or break inside the distributor. I honestly don't know how much work it is to acess this wire inside the dist.

How about the basics of cap & rotor, everything OK there? Did you pull a plug to be sure it's definately a no spark situation?

jarroyo · 05-09-2005, 05:25 PM

yes I've verified that there is no spark. also if you have access. can you post up a vacuum line diagram for me?

928ram · 05-09-2005, 06:49 PM

I'd look into the green wire, from what I've heard from others it can cause complete loss of ignition or can be intermittant. It's possible that the control box went bad, but since it did fire for you I'd leave that as the last suspect. Another thing that's rare but does happen is ignition switch is worn out but this will normally show up as no starter function.

The service manual doesn't show any vacuum system charts for the L-jet, I have 3 rather rough pictures that I have to convert from .tif to post; I'll try one to see if it's readable then go from there:

928ram · 05-09-2005, 07:02 PM

2nd one:

THe server isn't taking the files right now, I'll have to try the other 2 in the AM

I don't know how much help they'll be, everything's there but there's no labels on the components. You might start another thread to see if someone out there has an intact underhood label they can snap a pic of.

jarroyo · 05-09-2005, 08:05 PM

the ignition switch sounds probable since i thought it was the relay and jumpered it. after doin so it cranks. reason I need vac diagrams is that since the car sat for so long, some rodent got under the hood and gnawed all the wiring and vac lines so I've already replaced all the plug wires and coil now just need to do the vac lines. a friend told me that it could be possible that I'm flooding the motor not have the vac line to the fuel pressure reg hooked up. I really don't know since I've never worked on this type of fuel system before. it's L-jet correct?

928ram · 05-10-2005, 06:39 AM

It is L-jet, which was used '80-84 USA models.

Still can't get the other pics uploaded and they are the ones with all the vac lines on them, I'll keep trying unless you want to PM an e-mail add. and I can send them direct in the orig .tif format.

928ram · 05-10-2005, 08:49 AM

Trying

928ram · 05-10-2005, 08:53 AM

one more

928ram · 05-10-2005, 08:54 AM

There we go. Hopefully there's enough info to help out.

MPDano · MPDano's Garage

These are great charts. just what I needed.