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mattcfish
Samba Member
Joined: October 24, 2006
Posts: 565
Location: Bellingham, WA
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 Posted: Thu Jul 07, 2011 4:13 pm Post subject: Digijet "Calculatous Eliminatous" bad idle |
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Every year I like to touch on this subject because after 8 years of ownership my Vanagon still idles like crap (Lumpy "Blop, blop, blop, blop"). I've heard others that have old engines that run way smoother. Runs rich (smells rich) at low RPM's. Maybe somebody has the magic answer that will kill this Ahab's white whale. I've spent the years eliminating what it's not.
It's not a mechanical problem. I'm on my third engine, the latest one has less than 3000 miles on it and every bit of it is like new. Loads of nice even compression. No vacuum leaks.
I've done all the usual Bentley electrical tests on the ECU plug and everything checks out.
I've beefed up all the grounds and added extra.
New:
Breather tower
temp 2 sensor
Vacuum hoses
Fuel pressure regulator
Idle stabilizer
Plug wires and plugs
Cap and rotor
O2 sensor
Rebuilt:
injectors (and flow tested)
Swapped out:
AFM (two units, one has factory adjustment the other has been tweeked up and down manually), both test good on temperature curve.
Throttle body and TPS (3 different units)
Coil
Distributor, Hall unit and vacuum advance (3 different ones)
Ignition control unit (3 different ones)
ECU (2 different ones)
The cold start valve has been tested and works properly.
Fuel pressure is fine.
Timing...with the stabilizer disconected, does not like to run at 5 degrees retard (factory), best "crappy" idle is reached at about 3-5 degrees advanced. Any more advance and the idle starts to surge badly.
Idle vacuum is usually lower than 15...obviously because it's running with the wrong mixture. Valves and heads are new.
No exhaust leaks.
Come on Gurus, what am I missing?
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71 Bay Window
75 BMW 2002
76 BMW R90S
85 Vanagon with 2.2L upgrade |
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psych-illogical
Samba Member
Joined: October 14, 2004
Posts: 1181
Location: AZ
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| Posted: Thu Jul 07, 2011 4:39 pm Post subject: |
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I went through the same exercise w/ mine. Although the idle is still a little bit rough it's certainly not enough to be irritating. The one thing that I didn't see in your list was the charcoal canister and its vacuum operated valve. I did everything you did plus that. I didn't have to replace my ECU but I did everything else you listed. Have you hooked up a vacuum gauge and watched it while it's running? That might give a little clue. I was thinking of something like a sticking valve but I guess that's highly unlikely since you've been through a couple of engines. I run my timing a few degrees more advanced than factory but that's cuz I'm at 7000 ft. Have you tried pulling the catalytic converter out of the system? Maybe it's just a little plugged. The exhaust flange is the same so you can just remove the cat and bolt the muffler up without the cat being there. I dunno, I'm just grasping at straws and throwing out an idea or two.
Good luck.
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83 1/2 Westy waterboxer
'57 Beetle-sold 
Coupla '81 BMW motorcycles (R80G/S; R100RS)
'96 BMW R1100GS |
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TremcladWhite
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Joined: September 15, 2008
Posts: 58
Location: Vancouver, BC
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| Posted: Thu Jul 07, 2011 11:25 pm Post subject: |
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I don't see the wiring loom in the list either... what i'm finding in my van is that where the wire has been exposed to heat (nearest the engine) the old plastic jacket is breaking down, and the stranded copper wire inside begins to break down too. On a couple of the circuits I found local areas of high resistance, so I cut them out and soldered in new hunks of wire. Perhaps one of the wires in your idle/ignition/ECU circuits is going bad and causing the funky idle.
One of the projects on my list of good intentions is to get an old digijet loom for the engine bay and re-wire the whole thing and then swap it into my van. That project hasn't happened yet though, mostly because my van is running well these days.
My Bentley is downstairs in my van, but in there somewhere is a series of tests that you can do from the ECU plug with a multimeter and it will identify the bad circuits/components for you.
Edit: loom rebuilding from the best threads sticky. |
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mattcfish
Samba Member
Joined: October 24, 2006
Posts: 565
Location: Bellingham, WA
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| Posted: Fri Jul 08, 2011 9:49 am Post subject: |
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| psych-illogical wrote: |
I went through the same exercise w/ mine. Although the idle is still a little bit rough it's certainly not enough to be irritating. The one thing that I didn't see in your list was the charcoal canister and its vacuum operated valve. I did everything you did plus that. I didn't have to replace my ECU but I did everything else you listed. Have you hooked up a vacuum gauge and watched it while it's running? That might give a little clue. I was thinking of something like a sticking valve but I guess that's highly unlikely since you've been through a couple of engines. I run my timing a few degrees more advanced than factory but that's cuz I'm at 7000 ft. Have you tried pulling the catalytic converter out of the system? Maybe it's just a little plugged. The exhaust flange is the same so you can just remove the cat and bolt the muffler up without the cat being there. I dunno, I'm just grasping at straws and throwing out an idea or two.
Good luck. |
Yes, I swapped out the vacuum valve to the charcoal canister. I also tried blocking off the vacuum line to it and to the brake booster. No change.
I haven't taken a vacuum reading since I put the new motor in. The heads and TRW valves are new and lapped in perfectly. The lifters are new and set at 1/2 turn.
I removed the Catalitic converter as well.
The van has great throttle response, but is jerky when you try to drive under 15mph. The worst thing about the idle is the unburnt fuel smell. It does not smoke but the exhaust smell is always present at idle.
Funny thing about you talking about altitude. One time I was driving high in the mountains. I noticed something wrong, the van was idleing smoothly. I haven't been able to figure out why.
My current theory is that both AFM's I have... or both ECU's I have are faulty. Even though they pass all the electrical tests. I wish I could borrow a known good one from somebody, but everyone I know have Digiphants.
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71 Bay Window
75 BMW 2002
76 BMW R90S
85 Vanagon with 2.2L upgrade
Last edited by mattcfish on Fri Jul 08, 2011 9:58 am; edited 2 times in total |
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mattcfish
Samba Member
Joined: October 24, 2006
Posts: 565
Location: Bellingham, WA
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| Posted: Fri Jul 08, 2011 9:54 am Post subject: |
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| TremcladWhite wrote: |
I don't see the wiring loom in the list either... what i'm finding in my van is that where the wire has been exposed to heat (nearest the engine) the old plastic jacket is breaking down, and the stranded copper wire inside begins to break down too. On a couple of the circuits I found local areas of high resistance, so I cut them out and soldered in new hunks of wire. Perhaps one of the wires in your idle/ignition/ECU circuits is going bad and causing the funky idle.
One of the projects on my list of good intentions is to get an old digijet loom for the engine bay and re-wire the whole thing and then swap it into my van. That project hasn't happened yet though, mostly because my van is running well these days.
My Bentley is downstairs in my van, but in there somewhere is a series of tests that you can do from the ECU plug with a multimeter and it will identify the bad circuits/components for you.
Edit: loom rebuilding from the best threads sticky. |
I have performed all of the multimeter tests to the wiring loom and all it's components per the Bentley manual at least a half dozen times. I wish it was a wire, but I can't find any issues.
Two more clues: When the temp 2 sensor is disconnected the idle improves instantly.
When the O2 sensor is disconnected very little change is evident. Wiring tests good.
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71 Bay Window
75 BMW 2002
76 BMW R90S
85 Vanagon with 2.2L upgrade |
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mattcfish
Samba Member
Joined: October 24, 2006
Posts: 565
Location: Bellingham, WA
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| Posted: Mon Jul 11, 2011 11:46 am Post subject: Chumps Stumped? |
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I gather the Chumps are as stumped as I am. Of all the things I've done, which needs to be checked again?
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71 Bay Window
75 BMW 2002
76 BMW R90S
85 Vanagon with 2.2L upgrade |
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mattcfish
Samba Member
Joined: October 24, 2006
Posts: 565
Location: Bellingham, WA
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| Posted: Mon Jan 06, 2014 9:35 pm Post subject: Idle mystery solved! |
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Wrong cam. Very custom grind that goes beyond the limits of stock injection.
12 degrees of overlap measured at the cam. 106.5 lobe center separation.
I took the time to put the engine on a stand, fabbed up some solid lifters for measurement, attached a dial indicator to read the exact movement of the pushrod at the cam ( not the valve).
Tencent (remember him) measured a stock 2.1 cam at the lifter and got these results at .050 lift
IO= 5 BTDC
IC= 40 ABDC
EO= 39 BBDC
EC = 2BTDC (note: BTDC not ATDC)
Overlap= 3 degrees
Intake Duration 225
Exhaust Duration 217
LSA= 109
I think Tencent may have been measuring a Gowesty cam though. According to Lucas (at GW) there cam is identicle to stock but has a tighter LSA of 109 degrees, the stock cam should actually be even wider at 112.
My cam measured at .050" lift.
IO=9 BTDC
IC=43 ABDC
EO=35 BBDC
EC= 3 ATDC
Overlap = 12 degrees
Intake Duration 232 degrees
Exhaust Duration 218
LSA= 106.5
There just was no way to tune this motor with that tight of an LSA and overlap like that. That's why I had such low vacuum at idle. Stock closed loop EFI needs sufficient vacuum at idle to work properly. The wide overlap may also be causing some exhaust reversion at low rpm's which doesn't help matters.
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71 Bay Window
75 BMW 2002
76 BMW R90S
85 Vanagon with 2.2L upgrade |
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