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912e l-jet engine cuts out when revved

Hi, all.

I'm in the final stages of restoring a 912e.

I replaced most of the peripheral items related to the engine and FI system: new fuel tank, fuel pump, fuel filter, double relay, voltage regulator, NOS air flow meter, fuel pressure regulator, air filter, ignition wires, spark plugs, and all vacuum hoses.

I also installed a Pertronix II ignitor and coil, adjusted the valves, and set the timing.

The engine starts up and idles fine. However, it cuts out when I try to rev it.

Only other problem is that the alternator is not charging well. I had it tested, and it came out fine. I cleaned the contacts and reinstalled it, but the alt light is still coming on. It's getting 12.5 volts to the battery with engine running now. It had only been getting 11.5 before I pulled it and cleaned the contacts. I don't think poor charging would keep the engine from revving, but I'm throwing it out there just in case.

Any thoughts?

Thanks!




Last edited by IanLarsen71; 03-04-2019 at 09:59 AM.. Reason: minor corrections
Old 03-04-2019, 08:26 AM
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Just an update on this. Over the weekend the engine would cut out any time I tried to rev it. Today it's slightly different. It will rev evenly up to 3000 rpm (sometimes 3500) but then stops and loses power even though I still have my foot on the gas. It then stumbles a bit but ultimately returns to idle.

Here's a video of what's happening: https://flic.kr/p/2eXuPnd
Old 03-04-2019, 10:00 AM
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You need to recheck everything you have installed, and try to get a baseline established. Are you sure the motor is mechanically sound? Assume nothing is good or correctly adjusted. These are simple cars with simple fuel injection systems that will not work if one thing is out of place!

Start with one system, fuel, ignition or air. Do you have the workshop manual to test the fuel injection components? If not go to the 912bbs site and check the sticky post.

I would start with timing, is the firing order correct? Pull the spark plugs and see what color and if they are fouled.
What fuel pressure do you have? This is really important for the injection to function.

Also the fuel injection pulls a lot of amps running, so if your battery and alternator are weak it can cause a lot of issues.

Good luck, take your time and be careful when working on it running, make sure fuel isnít spraying all over in a fine mist, have a fire extinguisher in reach.
Old 03-05-2019, 04:19 AM
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Thanks. I have the l-jet manual and have checked everything. Only item I can't confirm is working correctly is the thermo time switch, and that's only because I can't get the connector off to test it. (It's tucked too far back underneath the intakes to reach it well.) I'll send the ECU out to be tested and repaired if necessary.

All cylinders are firing and the plugs are nice and clean. I adjusted the valves and set the timing a few weeks ago. The firing order is correct. I haven't run a compression test yet, but even if I have a compression problem I don't think that would keep the engine from revving up.

I'll check fuel pressure and run a vacuum test this week. I may switch out the fuel pump again to see if that helps.
Old 03-05-2019, 05:36 AM
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My first guess is that the airflow meter 'flap door' is not opening as it should, or the pickup arm that slides on the potentiometer element inside the AFM is not making the proper contact. In the above first case, any vacuum leak between the AFM and the throttle valve will prevent proper functioning of the AFM. This includes any malfunctioning (leaking) devices attached to the air intake elbow. Test this by disconnecting the hoses of all of the devices from the elbow and covering the holes temporarily with duct tape. Be sure to also plug the vacuum lines. If that doesn't make a difference, try spraying some carb cleaner around the devices and the elbow itself with the engine idling. Sometimes there are vacuum leaks in the bellows or up at the throttle switch that are hard to find.
If all this fails, I'd suspect the AFM itself, as what you're describing makes this logical since the idling part is pretty failsafe, but the revving part requires the flapper to open and send a correct signal to the ECM.
Did you ever have this engine running well or did you buy it in this condition?
Old 03-11-2019, 08:12 PM
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Thanks. I bought this car in sort of half-restored condition. The previous owner bought it to restore and did most of the cosmetic work -- bare metal respray, sourced new leather, installed new carpet and headliner, etc. -- but then he decided to sell. The engine had not been started in over two years when I bought it from him in August. I've done everything else.

The engine idles smooth and has good compression: 129, 134, 129, 129. These numbers are from a cold engine. I haven't run a compression test with it warm.

Regarding the engine speed limitations, the new fuel pump I installed was making a whining sound, so last night I reinstalled the old Bosch pump. I measured the fuel pressure afterward, and it was right at 35 psi. I revved the engine, and suddenly the entire problem was gone.

So, this morning I actually took it for a drive.

And three minutes in, it started to stumble again and the entire problem came right back.

I thought the problem was solved but no such luck, I'm afraid.

The AFM is brand new. I found it NOS on eBay and had the seller test it before I committed to buying it. It tested just fine.

Would a bad ECU cause any of these problems?

Or maybe there's a clog somewhere in the fuel lines?

Thanks again.

Ian
Old 03-12-2019, 09:41 AM
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For anyone who might be interested, here's a list of everything the previous owner and/or I have done to the car:

Renovation List
Porsche 912e
VIN 9126001141

Car is believed to have had four owners. The first owner is unknown. The second owner, from Charlottesville, Virginia, purchased it in the 1980s and kept it for roughly 30 years. Third owner, from Richmond, Virginia, purchased it in March 2017 and began a full restoration, which he did not complete. The current owner purchased the car in August 2018 and completed the restoration in early 2019.

WORK COMPLETE

Body

Bare Metal Respray – color change from Sahara Beige to Minerva Blue Metallic *
Replaced front valance #
Replaced front impact strip #
Replaced wiper fluid reservoir #
New wiper fluid reservoir filler hose #
New wiper fluid filler hose cap #
New front bumper baffles *
New plastic trim/piping between front fender and front wheel well panel #
New front trunk hood seal *#
Replaced front Porsche badge #
New front fender piping #
New windshield wiper arms and blades #
New windshield wiper mount gaskets, bolts, and caps #
New rocker panel covers *
New rocker panel rubber trim *
New rocker panel end caps #
New front windshield gasket and metal trim *
New sunroof gaskets and trim #
Sunroof tracks cleaned and lubricated #
New decklid ventilation grill T-bolts #
New decklid bumpers #
New decklid gasket *
New rear impact strip *
Installed Euro rear buffers/bumperettes *
New rear bumper baffles *
New trim/piping between body and rear wheel well panels *
New exterior door handle gaskets *

Interior

New lower door sill covers and trim *
New door window gaskets and trim *
New door weather stripping #
New quarter window gaskets *
New rear window gasket and metal trim *
New Momo Prototipo steering wheel *
New horn button *
New shifter boot #
New handbrake boot #
New black German vinyl headliner *
New A pillar trim *
New B pillar trim *
New seatbelt boot *
Replaced front seatbelts *
New Interior dome lights #
New black sliverknit carpet *#
New rear seat well insulation *
New rear wheel housing panel sound absorbers, left and right *
New rear panel/package shelf insulation *
New leather front and rear seat upholstery – cashmere beige *#
New leather door cards – cashmere beige *#
New leather rear/quarter window cards – cashmere beige *#
Reupholstered upper door garnish in leather – cashmere beige #
New leather door pockets – cashmere beige *#
Reupholstered quarter window garnish in leather – cashmere beige #
New rear package shelf cover – black vinyl *
New door vapor barriers #
New rear view mirror #
New sun visors #
New brake and clutch pedal covers #
New accelerator pedal #
New shifter bushings, front and rear #
New passenger side footrest#

Fuel System

New fuel tank *
Replaced fuel expansion tank and hoses behind driver’s headlight #
New fuel level sender, gasket, and protective bracket #e
New fuel tank/fuel filler joiner hose #
New fuel tank upper hoses #
Replaced fuel filler pipe and cap #
New fuel pump #
New fuel filter #

Wheels/Brakes/Drive Shaft

Rebuilt brake calipers #
New brake pads #
New brake master cylinder #
Replaced brake fluid #
New brake fluid reservoir drain tube #
New rubber brake lines *
New rear metal brake lines #
New Tires *
New inner passenger side CV joint boot #

Electrical

Replaced front running lights #
New battery *
Installed H1 headlights *
New headlight gaskets *
New fresh air fan motor #
Converted from manual to power windows *#
Door window motors and mechanisms lubricated #
New power window wiring harness #
New passenger door window switch wiring #
New power window relay and relay wiring #
New turn signal switch #
New door window switches #
Rebuilt rear lights #
New rear license plate light bulbs #
New LED lights for dash instruments #
New wiper fluid pump #
Confirmed alternator function & cleaned contacts #

Engine/Engine Bay

New charcoal canister hoses #
New airflow sensor #
New temperature sensor II #
New spark plugs #
New spark plug wires #
New fuel injectors #
New vacuum hoses #
New dual fuel pump/fuel injection relay #
New voltage regulator #
New engine bay insulation #
New decklid shock #
Replaced oil breather #
New oil breather gasket #
New fuel pressure regulator #
New rear relay panel cover #
New Pertronix ignition coil #
New Pertronix Ignitor II #
New distributor cap #
New air filter #
New fan belt #
New muffler *
New oil pressure sensor #
Oil change #
New oil filter #
Cleaned oil strainer #
New oil strainer gasket #
Adjusted valves #
Adjusted timing #
New valve cover gaskets #
Repaired heat exchangers #
Compression test (see below) #

* Denotes work done solely by third owner in 2017/2018
# Denotes work done solely by current owner in 2018/2019
*# Denotes work started by third owner and completed or corrected by current owner in 2018/2019

COMPRESSION TEST RESULTS

Cold engine at 1500 ft. elevation 3/10/19:

Cylinder 1 – 135 x 0.96 = 129.6 at sea level
Cylinder 2 – 140 x 0.96 = 134.4 at sea level
Cylinder 3 – 135 x 0.96 = 129.6 at sea level
Cylinder 4 – 135 x 0/96 = 129.6 at sea level
Old 03-12-2019, 09:43 AM
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I've had this sort of problem with my 912E a few times and I've always blamed it on fuel delivery and it always ended up being ignition related.
Old 03-12-2019, 11:17 AM
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Jrboulder -- what was the specific ignition issue causing the problem in your case?
Old 03-12-2019, 02:08 PM
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Update:

When I measured fuel pressure at 35 psi, I installed the gauge at the fuel rail, the ignition was on, engine was off, fuel pressure regulator vacuum hose was removed, and AFM door was held open with a screwdriver. In that case, it quickly rose to 35 psi and stayed there.

After the problem returned, I limped home and let the engine cool back down. Then I measured the fuel pressure again, this time with the engine running, though I didn't remove the fuel pressure regulator vacuum hose this time. (should I have in that situation?)

Under these conditions, the fuel pressure was steady at 30 psi with the engine idling. When I revved the engine, fuel pressure dropped to 10 psi. Then the engine stumbled when it hit 3000 and slowed back down again. As it slowed, fuel pressure rose back up to 30 psi and stayed there as the engine idled.

I ran out and bought a cigar the afternoon. I'll do a cigar test for vacuum leaks , hopefully before the sun goes down tonight.

Is any of this consistent with a failing ECU?

Last edited by IanLarsen71; 03-12-2019 at 02:19 PM..
Old 03-12-2019, 02:11 PM
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Quote:
Originally Posted by IanLarsen71 View Post
Jrboulder -- what was the specific ignition issue causing the problem in your case?
One time it was corrosion on the coil wire and another was a plug wire not fully seated.
Old 03-12-2019, 03:17 PM
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Well, I spent some time on this last night and it’s better but still not fixed.

I blew out the fuel lines in the engine bay as well as the return line. I didn’t blow out the line from the pump to the engine. I’ll do that tonight when I have time to jack up the car again.

I also found a tear at the bottom of the air intake boot. I likely created that myself in recent days when triggering the fuel pump with a screwdriver in the air flow sensor. I taped it up and ensured there were no more leaks in it. I'll order a new one on eBay.

Incidentally, the air flow sensor is a NOS Bosch unit I found on eBay. I simply bolted it on and plugged it in, as I was told they don't need any adjustment out of the box, but please tell me if you disagree with that.

It struck me that the new fuel pressure regulator I installed had a larger sized outlet for the vacuum hose than the original Bosch unit, thus requiring a larger hose than usual and it might not be getting a compete seal at the plenum, which has a smaller outlet. So I reinstalled the original Bosch pressure regulator with a new vacuum hose. The fuel pressure immediately stabilized at 35 psi and stayed there as I revved. It no longer tried to stall out as I revved it by hand, either. The idle was much smoother and it was easier to adjust the idle speed as well. The engine is much quieter as a result. It also got up to normal operating temperature more quickly than it had before.

However, when I took it for a drive I still didn’t have full power, and it did still try to stall once it was under load. When I got it back to the house I was able to get it above 4000 before it tried to stall, rather than the 3000 I was managing before.

So, that vacuum line must have been part of the problem, but there’s still something going on. If blowing out the last fuel line doesn't fix it I'll start looking at wiring.

I certainly welcome other suggestions as I go.

Here's a video I took last night of the car idling. Nice and smooth. Unfortunately, it still stumbles and tries to stall when i get it above 4000 rpm.

https://www.instagram.com/p/Bu_YiT2lN4K/?utm_source=ig_web_button_share_sheet

And here's the short drive I managed to get in before the engine started stumbling again:

https://www.instagram.com/p/Bu_aWXQF8GT/?utm_source=ig_web_button_share_sheet

Last edited by IanLarsen71; 03-14-2019 at 07:46 AM..
Old 03-14-2019, 07:08 AM
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Interesting post and curious to find out what is the cause... I always apply don't fix what ain't broken and my cars are mostly running fine. With the amount of new parts installed on the engine it can be a long search I'm afraid.

My experience when I had an issue:
- airleaks...had it a few times, keep looking and double check as this has big impact on how this engine runs. Double check the elbow 90degree one at oilbreather as well + make sure oilbreather gasket is tight as well. I taped some lines and connections with self vulcanizing tape to be 100% sure there is no way it can leak. Very reliable since.
- never had any fuel issues
- coil connector got corroded
- points warn out
- damaged spark plug wire, they now have extra protection to protect them from engine heat.

Never had anything major, just simple things, but it can be a pain to track it down...hang in there!

I use an old school vacuum meter to do a quick check the engine health. It might help you diagose your issue if you're sure timing, dwell, valve adjusted etc is all fine. On one car I changed the distributor angle which made a big difference on how quick the car picked up power. Also recommend to check airbox for cracks or a poor seal.

I'll keep my fingers crossed for you and hope you find your fix so you can really hit the road and enjoy your ride.
Old 03-14-2019, 10:54 AM
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In the hopes of keeping this thread alive I'll throw out some additional thoughts that might help.
I realize that you're not a novice and have most likely checked these things, but repetition never hurts.
1. The more I read your symptoms, it might be a restriction of fuel "upstream" of the pump since initially fuel pressure comes up and holds at idle (which requires very little fuel volume.) I can't remember if the 912E has a screen filter before the pump. It's also possible that some sediment or scale is in the tank and eventually and temporarily blocks fuel to the pump.
2. Double check the fuel return line from the regulator and make sure that the vacuum line to the regulator has no leaks and goes to the so-called air distribution chamber under the throttle valve.
3. Just to check, try disconnecting and plugging the vacuum line to the FP regulator, open the fuel filler cap to vent the tank and see if there's any difference.
4. I don't know if you've fixed it, but that alternator light staying on stays in the back of my head. If it has an LED in it, try changing to an oldschool bulb as some circuits require a certain resistance. Also, double check the several grounds that are at the rear of the engine, just to the right of center coming out of the large loom. Then check the connector to the ECU and make sure it's fully clicked-in. And, most important, physically check the ground strap from the engine/gearbox to the chassis and the front ground from the battery to the body.
And....another edit.....be certain that the Pertronix is wired correctly since the ECU takes a reading from the negative side of the ignition. Check the advance/retard lines and (very low probability) check to see if it has a VW spec rotor with a rev limiter installed.
As someone posted above, this is a relatively simple system, but I'll add... 'until something goes wrong.' Cars of this era were a mixture of a digital computer attempting to analyze various inputs from purely analog, mechanical devices with no provision for feedback or adjustment. All they could really do is fall back to limp-home mode.
And, finally, your car is absolutely beautiful...one of the best colors Porsche ever offered, especially with tan interior.
Good luck
Bill

Last edited by WFBowen; 03-18-2019 at 09:10 AM..
Old 03-18-2019, 08:53 AM
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Thanks, Bill.

I'll try to respond to some of these things here. Incidentally, I'm always happy to receive advice from a Bowen. My grandmother was a Bowen. That part of the Bowen family traces its roots in the US to settlers in St. Mary's County, Maryland in the 1600s. My grandmother was born in Iowa in 1900, and I believe the family continued to move westward from there

Anyway.....

Regarding possible fuel blockages, I blew out the fuel lines from the fuel filter through to the return hose and didn't seem to have any problems. I haven't blown out the line from the pump to the filter, though. I'll try to get to that this week.

There's no filter before the pump on this car. Also, the previous owner replaced the tank as part of the restoration, but he seems to have used a Dansk tank, which is the type without an internal screen. Apparently these tanks won't accept the standard internal screen, either. I inspected the fuel tank for debris and can't see any. There was a Bosch fuel pump on the car when I bought it. Not knowing how old it was, I replaced it with a new unit from Pelican, though it wasn't Bosch. I reversed the flow of the Bosch unit after I took it out, and I did find a small amount of debris caught in the small screen on the inlet side of the pump. As I've been trying to sort this problem, I reinstalled the Bosch unit to see if it made any difference. That unit does seem to be working well.When I took out the unit I bought from Pelican, I reversed the flow on that one too. This time there was no debris in the filter. For now, I'm keeping a clear hose mounted between the fuel tank and the pump. That was I'll be able to see any debris passing through, but I haven't seen any.

The vacuum hose going to the fp regulator is brand new and it positioned correctly. I'll double check vacuum on it, though.

I'll also try opening the filler cap as you suggest.

The alternator problem remains. I don't think I put an LED light in that one, but I'll double check.

I did a quick visual inspection of the grounds and didn't see anything obvious. Should I be looking for anything other than tight connections and no corrosion?

Regarding Pertronix, I"m not sure how it could be wired incorrectly. Red to positive coil and black to negative. Am I missing something?

Thanks.
Old 03-18-2019, 12:41 PM
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Replace head temp sensor at # three cylinder it,s under the sheet metal ,these were a problem Even when these cars were new. Good luck,lee.
Old 03-19-2019, 08:39 AM
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Ian:
Here's a long shot...... I looked at your video of the car idling (where you open the decklid.) I'm viewing this on an Ipad, so the image is small, however I don't see your vacuum advance line "t-ing" from the distibutor/egr to the throttle body vacuum takeoff. Mirage? Senior eyesight? any of the above.
Bill
Old 03-19-2019, 07:24 PM
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Quote:
Originally Posted by Nukar sales View Post
Replace head temp sensor at # three cylinder it,s under the sheet metal ,these were a problem Even when these cars were new. Good luck,lee.
Thanks, Lee. I did that a week or so ago.
Old Yesterday, 09:59 AM
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Quote:
Originally Posted by WFBowen View Post
Ian:
Here's a long shot...... I looked at your video of the car idling (where you open the decklid.) I'm viewing this on an Ipad, so the image is small, however I don't see your vacuum advance line "t-ing" from the distibutor/egr to the throttle body vacuum takeoff. Mirage? Senior eyesight? any of the above.
Bill
Someone else brought this to my attention the other day as well. You're correct that there was no t-connector present. When I bought the car, the port on the driver's side of the throttle body was plugged with a rubber cap. I routed the new vacuum lines in the manner shown in the attached image from the l-jet guide for our cars. Turns out that image is incorrect, so I went with the t-connector joining the distributor canister, EGR, and driver's side throttle body together. The car started up a bit quicker and smoother, but it didn't solve the problem, I'm afraid.

Ian
Old Yesterday, 10:04 AM
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