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Wow. I really appreciate the words of advice from the true experts on this issue. Every single post.
Try to get that on a Mustang, Vette, or any other forum for that matter!
I'm thinking back on when I got in the car a month or so ago, turned the key and it just cranked as though it was out of gas. I thought "Crap. My LH is done" because I'd heard that LH failure is inevitable in '87+ cars and I was fearing the day. Then I thought "Relay". Wishful thinking, I guess. If it turns out to be my LH, at least my GT was kind enough to let it happen in the convenience of my garage.
So my next step will be to test the LH with a known working unit. I have the '88 that has a good LH.
I'll post the results.
I've only skimmed the thread, so if I missed something please excuse me.
You said you jumpered the relay and the fuel pump ran. Did you try starting it? If you tried starting it and it did NOT run, then I would suspect the LH. If you did, and it ran, then it's not the LH. But since you have an 88, you can swap those and see if that solves it.
Other things to suspect are the crank position sensor. If this fails, the pump will not run.
Also there is a trouble shooting guide in the links in my signature.
Hi John
I don't keep exact figures of MY versus quantity sent to me for repair. But comparing number of 928s sold each year and the proportions of the number of each model that I see, then my strong feeling is that GTS are just as failure prone as the earlier models.
Bosch didn't change the design of the troublesome "tile" through the life of the 928.
If I had to guestimate a likely life of an LH I would say 75k miles/10 years. Lots survive longer than that, but there is a known risk of failure when those thresholds are passed.
I guess I have repaired a couple of thousand by now...
Originally Posted by John Veninger
My vote is the LH.
As mentioned, see if anyone local would do a swap with you to verify.
Is your LH is the original one from Porsche? Appears the "newer" LH computers have held up better than the early ones, but that's just a feeling.
John and/or Louie could give us actual data as to the the quantity of failures they have fixed by year.
My 90GT still has it's original and have been thinking about sending it to Louie before it fails.
If I had to guestimate a likely life of an LH I would say 75k miles/10 years.
Oh no, I'm at 76K miles and way over ten years.
I hope it as couple of more months before the GT goes to bed for winter. I'll then send the LH to Louie for update.
Things that can shorten the life of an LH are using a normal 5A battery charger on a well discharged battery without first disconnecting the LH ECU 35way connector.
The resulting big current surge can kill the LH. So the object is to minimise such surges if possible. Also old spark leads that arc to the engine castings are known to be high risk.
Similarly high voltage "boost" starting packs can deliver substantially more than the recommended 16v maximum.
My rebuilds offer much better transient protection that the original tile.
Originally Posted by John Veninger
Oh no, I'm at 76K miles and way over ten years.
I hope it as couple of more months before the GT goes to bed for winter. I'll then send the LH to Louie for update.
All excellent pieces of information. To avoid the first instance, a heavily discharged battery should always be disconnected before receiving a charge, right?
I also heard that the positive post terminal in the engine bay should never be used as a connection point to jump start a 928. In fact, jump starting a 928 should be avoided if time allows for properly charging the battery. Is that true?
Originally Posted by John Speake
Things that can shorten the life of an LH are using a normal 5A battery charger on a well discharged battery without first disconnecting the LH ECU 35way connector.
The resulting big current surge can kill the LH. So the object is to minimise such surges if possible. Also old spark leads that arc to the engine castings are known to be high risk.
Similarly high voltage "boost" starting packs can deliver substantially more than the recommended 16v maximum.
My rebuilds offer much better transient protection that the original tile.
All excellent pieces of information. To avoid the first instance, a heavily discharged battery should always be disconnected before receiving a charge, right?
I also heard that the positive post terminal in the engine bay should never be used as a connection point to jump start a 928. In fact, jump starting a 928 should be avoided if time allows for properly charging the battery. Is that true?
Yes to both... :-)
__________________
John '86 Euro S2 16v
SharkTuned LH & EZ-F www.jdsporsche.com
Quote:
Originally Posted by John Speake
Things that can shorten the life of an LH are using a normal 5A battery charger on a well discharged battery without first disconnecting the LH ECU 35way connector.
The resulting big current surge can kill the LH. So the object is to minimise such surges if possible. Also old spark leads that arc to the engine castings are known to be high risk.
Similarly high voltage "boost" starting packs can deliver substantially more than the recommended 16v maximum.
My rebuilds offer much better transient protection that the original tile.
Here's my question.
In reading JPTL's thread on fuel delivery issue, I came across the two above posts regarding battery charging an the possibility of providing to much amperage to the LH, and damaging it. Though the original design provided for easy charging through the jump post (as it is called), should charging (not trickle - jump starting) take place as John suggests ?
His experience, and wisdom, is always respected.
What say the Wise ones ?
This issue is new to me and unfortunately I don't have the space to start troubleshooting and learning about this issue over the course of a couple of weeks, so I'm using you guys to help me prepare for what I need so that I can get the issue nailed in a short period of time. Your cumulative advice is as always invaluable, so thanks!
I'm going to start by second guessing myself and re-checking the relay. Taking the "relay-relay-relay" advice as gospel, I've replaced a seemingly good original relay with a NIB Werhle 20 240 073 (box labeled 141-951-253-B) so I believe that I'm using a good, correct relay and have hopefully eliminated what often seems to be cause #1.
From what I'm reading here, I might first want to do an electrical, followed by a physical diagnostic of the external pump and it's power circuit before I drain and drop the tank. So after I put my cigar down, I'm gathering that the first step would be: 1. Test the relay by getting a voltage reading at the pump while cranking the engine. If I get 12v, then the relay is good and proceed to Step 2. If no voltage, then the relay or wiring is suspect and start the troubleshooting process unrelated to the fuel pumps themselves, the tank and all related fuel lines. 2. Bypass/jumper the FP relay*, and take a voltage reading at the pump terminals - ignition on. If the I get a 12v reading but the pump isn't operating, the FP is jammed with debris, or it has simply failed. Skip step 3 and go to step 4. 3. If the pump appears to be operating, then per Jim, get a measurement of fuel flow at the return hose. 4. If the FP is operating but there is no flow at the return hose, then drain the tank. 5. Check for blockage between the tank and the FP, starting by removing the feed hose from the tank to the FP (#4 in the schematic). 6. If feed hose is deteriorated to point of complete blockage, check for debris in the FP and replace the feed hose. Even if it's not deteriorated, replace it. 7. After the feed hose has been replaced, before reconnecting the fuel pump, attempt to clear debris from the FP by briefly operating it in reverse. 8. If after the FP has been reinstalled and the system primed, the pump is not adequately pumping (volume test), the FP is defective - replace along with a new filter...
...or start troubleshooting the internal pump.
Please feel free to amend or correct me with any of my steps here.
*is the corrrect method of bypassing XXVI relay with a constant-on fuse-protected circuit connecting 87 and 30?
This post provides a nice algorithm for fuel delivery issue electrical diagnosis for the unexperienced with such. Good to save.
Thanks.
Andrew,
After double checking the health of the battery and giving it a full charge overnight (disconnected), I loosened the cluster of brown ground terminals adjacent to the CE panel, shot some contact cleaner on the loose connectors and retightened it. Then I unseated/unplugged the LH and reseated it.
Connected the battery and took a reading at the positive 10mm nut on top of the fuse block and the ground cluster. I got 12.27v.
With the relay in, I tried to start the car, but got no reading at the fuel pump/no start.
I jumpered the relay, reconnected the battery and the pump immediately ran. I tried starting it on the jumpered fuel pump, and it kicked over, but only stumbled. It never started and settled into an idle. I couldn't venture a guess as to whether this was a fuel pressure/delivery issue or an ignition issue.
I can just confirm that under a jumpered pump relay, the engine did kick, but never properly ran.
This is where I am at this point.
Next step is to borrow an LH and test the car, relay in place...... unless by the car kicking over under the jumpered pump - even the least bit, would rule out a bad LH.
Originally Posted by AO
Hi JP,
I've only skimmed the thread, so if I missed something please excuse me.
You said you jumpered the relay and the fuel pump ran. Did you try starting it? If you tried starting it and it did NOT run, then I would suspect the LH. If you did, and it ran, then it's not the LH. But since you have an 88, you can swap those and see if that solves it.
Other things to suspect are the crank position sensor. If this fails, the pump will not run.
Also there is a trouble shooting guide in the links in my signature.
Thanks Bertrand. I believe that any 87+ LH will work in my GT.
I would have just popped the '88 LH in to test, but the car's at Kevin's and I haven't had the time to get down there.
If my schedule let's me, I'll be at Frenzy - with the GT if I can swing it..
The appropriate way to do this test is to stick the suspect LH into a 928 that is known to start. If the known-good car doesn't start then the suspect LH is indeed dead.
If you put a working LH into a non-starting 928 and is starts then you also know that the suspect LH is dead. However, if the non-starting 928 doesn't start with a known-good LH you learn nothing except that you have at least one non-start issue that isn't the LH; you still don't know if the suspect LH is good or bad.
In the case of a 928 I was not very familiar with, I would never stick a good LH into it because maybe, just maybe, it is something in that 928 that killed the LH (bad wiring etc.)
I went through this same or similar scenario a couple of years ago with my 89GT. First intermittent starting problems and then no start. Went through all the easy diagnostics including new relays followed with the jumping the FP. Fuel rail pressured up, but no start. But I was in ECU-failure denial.
Garrity lent me spare LH (programmed for supercharger) and it started right away, but ran like crap due to off-standard programming - nonetheless it ran. Put in a Speake ECU with my GT chips, and has run well ever since.
You win, John! Beer's on me.
In fact, beers on me for everyone who posted here b/c LH failure became the common consensus as I provided more info.
I really appreciate the wisdom and the advice that allowed me to take the shortest distance between two points in the quagmire of electrical troubleshooting.
My car never left my garage on a rollback, I didn't have to call in the experts to make a house call, and I'm going to come out of this without a serious hit to my wallet (everything's relative in that regard, and I've been budgeting for this over the past few years).
So thanks again!
I borrowed a known working LH from a real standup guy who just happened to have a spare on hand and is local. How lucky is that?
Popped it in the GT and it started right up. Considering that it wouldn't start with the original LH, but with the loaned LH popped in under the exact same conditions, it immediately started, I can't imagine it being anything other than a failed LH.
John Speake, PM sent.
I'm also going to ask the moderators to update the title to this thread. Hopefully the next RL'er who is troubleshooting a similar situation can find this thread and benefit from the post-by-post troubleshooting guide that this thread became.
09-02-2015, 10:13 AM
