When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
o
I had a starting problem a month or so ago- seemed the fuel pump was not running. No problem, blew the cobwebs off my spare LH, installed the custom PEM into it and fitted the thing. Still would not start. Pulled the fuel pump cover off and got the wife to start it and it fired up. Problem solved? Actually no, tested the "duff" LH and it worked so not the LH. OK, so I pulled the fuel pump relay and a jumper fired the fuel pumps up. Tested the relay that worked OK so what could it be. A few days later again it refused to start - bugger! Thought about it and figured there might be a problem with the CPS - have not touched it since fitting it some 16 years ago. Went to pull the connector and the male side crumbled in my hands before putting any effort trying to separate it.
I have also started my annual maintenance and a week or so ago thought I could smell fuel in the pump region but no signs of spills. Decided to redo the wiring loom, fitted the connectors onto the main pump- jumped the relay and it fired up. Went to fit the connectors on the in-tanks pump- the positive terminal was easy to slip on, the negative terminal is something of a bear to fit- dropped the rear of the cradle a bit and managed to get it into position- as I pushed on the terminal I saw fuel dribbling out of the terminal block- bugger!
My 928 is pretty clean and well cared for but still these thing happen- my 928 is nigh on 30 years old- I reckon that is about 90 in human terms! Bottom line either we have to deal with the problems or pay someone an arm and a leg to do so. I am now working the LH/EZK wiring harness harness- did the engine harness a couple of years ago and it is holding up well. Decided this morning that I would remove the inlet manifold in part for inspection and in part to facilitate access to the wiring loom. In a few moments time I will hopefully fathom out a way to remove the engine hook adjacent to No1 cylinder so that I can get at the connector for the Hall trigger. If that comes apart in one piece all well and good- I reckon there is a fair chance it will fall apart in my hands as well. If it does fall apart better to find out now than whilst out on a run.
Bottom line one just has to keep on top of these things if one wants reliability. I also have the coolant shower to look forward to when I pull the crankcase drainage plugs!
So....plenty of testing and fault finding is pointing to a leaking intake manifold. ISV testing OK at this point. Air is being sucked in and obviously affecting stuff - I wondered what the whistling noise was!
Regardless, the intake manifold is coming off to see what's what underneath and while that's off......who knows?
What would the list of "to do's' be while the manifold is off? The tech mentioned injector seals for example....
Leaky intake manifold is a new one on me. Assuming the Hammer readout was clean, smoke testing should show where the leak is. But a refresh will fix that too.
On the intake refresh: Search for worf928's intake refresh guide and also Dwayne's Garage intake refresh writeup. Worf's is easier to follow I think and Dwayne's is very prescriptive and detailed. It is a great opportunity to make the car run like new again. Both are outstanding and I was able to complete my first refresh with those docs. (Don't forget to clock the TPS correctly!)
Our 928 parts vendors can set you up with a full set of parts for all the work - they have done this many times.
There are may intake refresh writeups on Rennlist with tips, dos/don'ts, and war stories. Enjoy! × ×
Last edited by chart928s4; 02-03-2021 at 01:38 PM.
So....plenty of testing and fault finding is pointing to a leaking intake manifold. ISV testing OK at this point. Air is being sucked in and obviously affecting stuff - I wondered what the whistling noise was!
Regardless, the intake manifold is coming off to see what's what underneath and while that's off......who knows?
What would the list of "to do's' be while the manifold is off? The tech mentioned injector seals for example....
The two hoses that connect the ISV to the system are a failure possibility- they can and do crack with age. We covered the ISV earlier.
The various breather hoses go soggy with age and oily vapour exposure
The knock sensors tend to crumble at the connector but can only be changed out with the manifold out of the way..
The combination idle switch/WOT switch has a tendency to fail with age on the WOT contact bar
The cheap and dirty flush of the ISV may have cleaned it to some extent freeing it up but...?
You need to check the filler neck for signs of leakage and probably better to reseal it.
Consider installing the Greg Brown baffle to help reduce oil ingestion .
The flappy actuator will invariably fail at some stage so a good candidate for replacement at this time
The rubber grommets sealing the manifold holding down bolts will probably need replacing- I boil mine in non detergent washing powder for 10 minutes- softens them up nicely!
Speak nicely to Roger and he will send you a comprehensive parts list for a full inlet manifold refurb. Examination can suggest what can be reused but...?
Replace the vac hose connectors lurking under there.
The bearings/seals for the flappy and the throttle butterfly can also go south- hopefully your tech can give you some advice on such.
Whilst the manifold is off have the two earth connections at the back checked/ cleaned
Not strictly necessary but also a good time to change out the CPS [/Roger does a good after market alternative]- doing mine at the moment
Inspect and check all the wiring and connectors for signs of attrition- replacing a chunk of my engine bay LH/EZK wiring at the moment- they tend to fraze close to the connector they feed.
The inlet manifold and sub manifold gaskets will probably need replacing
Sorry, one more question....if I had a magic wand and all of the above was completed, does that constitute an "intake refresh" or would it need to include getting the MAF checked and calibrated?
Sorry, one more question....if I had a magic wand and all of the above was completed, does that constitute an "intake refresh" or would it need to include getting the MAF checked and calibrated?
I just want to drive it in the summer!
Thanks again!
I think I covered most if not all of the inlet manifold refresh items but there are other items that you need to be sure of. In my experience the Bosch fuel injectors tend to clog up more than other injectors and now would be a good time to remove the injectors and have them calibration checked and ultrasonic cleaned- dirty injectors can easily lose you 10% of total power.
Another age related performance killer is the ignition leads. you could try taking a leak over them if you are into that sort of thing- if they are shot it will revitalise part of your anatomy! On the other hand simply run the car in a dark place and look carefully to see if you can see sparks tracking all over the place. You also need to do a vacuum test on the fuel pressure regulator and the two dampers. You also need to ensure that the passive vacuum system is holding tight vacuum or the flappy will not work. Your specialist should check the flappy is operating as it should- easy to do- if is working correctly the flappy spindle will turn through 90 degrees during initial start.
The fuel lines and the power steering high pressure hose are the main combustion wreckers. The engine wrecker is the flexplate clamp issue- if you have no secondary protection measures in place do so without fail as when TBF happens the first the owners knows about it is when the engine is buggered. I helped pioneer the loctite method 20 years ago and still use it but the best approach is to use Constantine's clamp. Roger also does a secondary bolt on clamp designed and offered by a fellow Brit that can be fitted in minutes with no disassembly required.
The MAF is something that tires with use. If you have a cat fitted the NBO2 sensor covers some of the error factor but not for full throttle conditions. The tired MAF under reads the airflow so it does no inject sufficient fuel.
I think I covered most if not all of the inlet manifold refresh items but there are other items that you need to be sure of. In my experience the Bosch fuel injectors tend to clog up more than other injectors and now would be a good time to remove the injectors and have them calibration checked and ultrasonic cleaned- dirty injectors can easily lose you 10% of total power.
Another age related performance killer is the ignition leads. you could try taking a leak over them if you are into that sort of thing- if they are shot it will revitalise part of your anatomy! On the other hand simply run the car in a dark place and look carefully to see if you can see sparks tracking all over the place. You also need to do a vacuum test on the fuel pressure regulator and the two dampers. You also need to ensure that the passive vacuum system is holding tight vacuum or the flappy will not work. Your specialist should check the flappy is operating as it should- easy to do- if is working correctly the flappy spindle will turn through 90 degrees during initial start.
The fuel lines and the power steering high pressure hose are the main combustion wreckers. The engine wrecker is the flexplate clamp issue- if you have no secondary protection measures in place do so without fail as when TBF happens the first the owners knows about it is when the engine is buggered. I helped pioneer the loctite method 20 years ago and still use it but the best approach is to use Constantine's clamp. Roger also does a secondary bolt on clamp designed and offered by a fellow Brit that can be fitted in minutes with no disassembly required.
The MAF is something that tires with use. If you have a cat fitted the NBO2 sensor covers some of the error factor but not for full throttle conditions. The tired MAF under reads the airflow so it does no inject sufficient fuel.
Fantastic info as usual Fred!
I meant to say that having the Ritech flex plate clamp was job #1, so at least that's done!
For the Brits reading this, my car will end up being "Trigger's Broom"
Double check your battery, battery ground strap. And all other grounds. I went through a similar issues and spent time and money chasing everything else. Had someone mention the ground strap. Visually it looked good but when I peeled back the plastic it was toast. Got one from Roger and the problem was cured.
My 1988 S4 had the same symptoms about 8 years ago. Refreshing the intake cured it completely. In my case I refreshed almost everything. However, in hindsight, not everything really required replacement at that time. The ISV was gunked up, but it worked fine after cleaning, so I still kept it as a spare. The throttle switch was fine. Sensors were fine. The hose to the ISV, part #92811063300, had a thru-wall perforation due to oil exposure, which resulted in a vacuum leak. Some of the other hoses were degraded, but others were still serviceable. If you are on a budget, and if you don't know the full service history, you could pull the intake and inspect the ISV and other wear items and do this before deciding what to clean or replace.
Double check your battery, battery ground strap. And all other grounds. I went through a similar issues and spent time and money chasing everything else. Had someone mention the ground strap. Visually it looked good but when I peeled back the plastic it was toast. Got one from Roger and the problem was cured.
My 1988 S4 had the same symptoms about 8 years ago. Refreshing the intake cured it completely. In my case I refreshed almost everything. However, in hindsight, not everything really required replacement at that time. The ISV was gunked up, but it worked fine after cleaning, so I still kept it as a spare. The throttle switch was fine. Sensors were fine. The hose to the ISV, part #92811063300, had a thru-wall perforation due to oil exposure, which resulted in a vacuum leak. Some of the other hoses were degraded, but others were still serviceable. If you are on a budget, and if you don't know the full service history, you could pull the intake and inspect the ISV and other wear items and do this before deciding what to clean or replace.
Thanks! All of FredR's list below has been checked or replaced, along with MAF wire resistance (good), MAF Boot (loose and now clamped tight rather than 'push on') and a few vacuum leaks now fixed:
1. The two hoses that connect the ISV to the system are a failure possibility- they can and do crack with age
2. The various breather hoses go soggy with age and oily vapour exposure
3. The knock sensors tend to crumble at the connector but can only be changed out with the manifold out of the way..
4. The combination idle switch/WOT switch has a tendency to fail with age on the WOT contact bar
5. The cheap and dirty flush of the ISV may have cleaned it to some extent freeing it up
6. You need to check the filler neck for signs of leakage and probably better to reseal it.
7. The flappy actuator will invariably fail at some stage so a good candidate for replacement at this time
8. The rubber grommets sealing the manifold holding down bolts will probably need replacing- I boil mine in non detergent washing powder for 10 minutes- softens them up nicely!
9. Replace the vac hose connectors lurking under there.
10. The bearings/seals for the flappy and the throttle butterfly can also go south- hopefully your tech can give you some advice on such.
11. Whilst the manifold is off have the two earth connections at the back checked / cleaned
12. Not strictly necessary, but also a good time to change out the CPS
13. Inspect and check all the wiring and connectors for signs of attrition
14. The inlet manifold and sub manifold gaskets will probably need replacing I decided to replace the ISV. I have a Lowe unit on its way from Germany, but with the current Brexit chaos, who knows when it will arrive?
Will report back when that's in.
Cheers
John
Last edited by jchasty; 02-05-2021 at 02:22 PM.
Reason: formatting
Took this photo for you today- it is the sub manifold showing the throttle and ISV hoses. The ISV hoses may be compromised if you have a leak. Those are a couple of years old but I eeked years out of the previous ones by fitting jubilee clamps over the bosses- they do not need to have the poo squeeezed out of them - just nipped up a tad to help seal things. before inserting them. I do the same over the bosses on the boot connections and on those I smear some RTV to help seal them- originally they were just a push fit but with age and rubber hardening up some I figured a bit of help would not go amiss.
Although it may not be apparent from the photo the inside of the sub manifold and the main item had no signs of oil whatsoever- I put that down to my breather system modifications. Looks a bit icky but have not had chance to clean it all up yet.
Took this photo for you today- it is the sub manifold showing the throttle and ISV hoses. The ISV hoses may be compromised if you have a leak. Those are a couple of years old but I eeked years out of the previous ones by fitting jubilee clamps over the bosses- they do not need to have the poo squeeezed out of them - just nipped up a tad to help seal things. before inserting them. I do the same over the bosses on the boot connections and on those I smear some RTV to help seal them- originally they were just a push fit but with age and rubber hardening up some I figured a bit of help would not go amiss.
Although it may not be apparent from the photo the inside of the sub manifold and the main item had no signs of oil whatsoever- I put that down to my breather system modifications. Looks a bit icky but have not had chance to clean it all up yet.
02-03-2021, 07:00 AM
