85 Digijet rich sloppy idle. I've tried everything.

[mattcfish]

85 GL (Digijet) 1.9L (2.2L conversion).
My idle is bad and has been for years. I've tried every diagnostic in the Bentley book, but I can't find the cause of the over rich, loping (pulsing) idle and poor jerky low RPM performance. Also getting poor fuel economy. Throttle response off idle is good, but you have to feather the clutch to keep it from bucking at low rpm.
I've tested every part of the ignition and injection system per Bentley.
The engine has been fully rebuilt, twice! No vacuum leaks, New crank case vent, checked for O2 coax cable issues. I've tried using a different ECU (could be two bad ECU's I suppose, but how to test for that...?)
Tried three different TB's and TPS switches. Three different dizzys, 3 AFM's, new coil, new injectors, fuel pressure regulator, tested charcoal canister vacuum valve, temp 2, O2...cat removed, etc, etc.
Other symptoms:
Will not idle with idle stabilizer (new unit and 2 spairs) bipassed at stock timing even with idle speed full out. If I try to lean out the AFM it runs worse and I loose off idle throttle response.
If I advance the timing to 5 to 7 degrees BTDC instead of ATDC it idles better, but not great, and still smells very rich and the starter labors to turn it over especially when hot.
I know the ECU is unlikely, but I'm plum out of ideas. If I mailed one of my ECU's to one of you guys with a Digijet that has a good idle, could you plug it in and tell me if it starts to run like crap?
Are there some other tests I should run or rerun?

..........the first rebuild was not done well. Budget build, Reused rod bolts failed and I through 2 rods at the same time after only 12,000 miles or so. Total loss. New engine has about 2500 on it. 1st rate ($$$$)rebuild using ARP rod bolts AMC Heads, TRW valves, lifters are new. GoWesty pistons etc.
Continuity tests on AFM, TPS, and 02 wires show good, but I must be missing something, it has to be a communication error in the circuit. If I disconnect the temp 2 while it's running idle improves a little, disconnect the o2...not much happens, disconnect the TPS.....nothing changes.

[Piledriver]

The "TPS" you have is an idle switch, on/off thing on that system (some have idle and WOT switches)

If the switch isn't adjusted just right, it won't idle well, the idle stabilizer will not kick in.
(OTOH it shouldn't idle horribly without it, it was the first part I bypassed on mine since it was flaky)

It sounds like something ...more basic may be wrong.

Compression #s?
Timing set at ?
(WBX usually like more timing than book)
Fuel pressure?
Injectors not jacked?

Replaced the 3" hose plenum to the FPR?
Any vac leak in that hose will drive you insane, and will not necessarily show up as low manifold vac.
Yes, it will run rich at idle from that.

I assume you also installed new injector seals.
The CIS seals (big, fat viton orings) are cheap, available, and work MUCH better.
(Thanks to Ray Greenwood for the tip)

[mattcfish]

The "TPS" you have is an idle switch, on/off thing on that system (some have idle and WOT switches)

If the switch isn't adjusted just right, it won't idle well, the idle stabilizer will not kick in.
(OTOH it shouldn't idle horribly without it, it was the first part I bypassed on mine since it was flaky)

It sounds like something ...more basic may be wrong.

Compression #s?
Timing set at ?
(WBX usually like more timing than book)
Fuel pressure?
Injectors not jacked?




Replaced the 3" hose plenum to the FPR?
Any vac leak in that hose will drive you insane, and will not necessarily show up as low manifold vac.
Yes, it will run rich at idle from that.

I assume you also installed new injector seals.
The CIS seals (big, fat viton orings) are cheap, available, and work MUCH better.
(Thanks to Ray Greenwood for the tip)

Thanks.
TPS adjustment is good. I've tried 3 different ones. However, unplugging it while running makes no change in idle. Should it? The idle stabilizer is working...it won't idle without it.
Compression #s? I haven't checked, but this this the 3rd engine, with same stinking problem. Heads, valves, pistons, sleeves.....all new. I should do a leak down just to get base figures, but I feel like I'll be wasting my time.
Timing set at ? 5 degrees BTDC (10 degrees advanced over Digijet spec)
(WBX usually like more timing than book)
Fuel pressure? Matches Bentley pressure checks. New regulator.
Injectors not jacked? Injectors are rebuilt , flow tested, and resistance is within spec. I also tried a seperate set of injectors without luck. Seals are new.

What's the FPR? All hoses to the manifold have been clamped or new. It does seem like a vacuum leak, but I feel like I've covered those bases.

More information on this forum http://www.thesamba.com/vw/forum/viewto ... 76#5524576.

[mattcfish]

Ran some tests today...

Leak down test shows no valve leaks....Only 3-4% leakage on all cylinders (perfect)...all into the crankcase. Compression is within 5 pounds on all cylinders 133 to 138 psi (GoWesty 2.2L pistons).

Plugs all look perfect. Marshmallow white/tan and gapped just right.

TPS working with a little resistance 0.6 ohms resistance at idle and full throttle (not in the switch, all in the wires). Infinity off idle to full throttle.

Injector spray patterns are perfect cones, no leak at shut off, fuel pressure is on the money.

The injector electrical tests were interesting. All of them tested 17.7 ohms resistance at the ECU plug. When jumping the terminals at the injector plug I get 1.7 to 1.8 ohms resistance. That means there is up to 1.8 ohms resistance just in the wires to each injector. If you remove that.... the injector resistance is perfect at 16. Would 1.8 ohms resistance in the wires be enough to contribute to my lumpy idle?

Note: If you pull any injector plug while the engine is idling, the idle speed only changes a little....that's weird.

Manifold vacuum at idle is only 8 to 9...steady with a little wiggle. No vacuum leaks found with starter fluid or propane tests. New TB seal and all hose and connectors rechecked.

Timing is now set at 10 BTDC. And the idle speed screw is screwed out to the point where a couple of threads are showing just to get it to idle fast enough with the stabilizer bipassed. Full advance is around 50 degrees if you include the vacuum advance.

I switch back to my good AFM with factory settings. Idle is still lumpy and stinky...no visible smoke...but sounds and smells bad. I've regained power and response with the extra ignition advance.

Any theories? Any ideas as to what direction I should head in?

[Piledriver]

I know you have gone through the ignition, but IME 99% of FI problems are actually gimpy ignitions...

(excuse the flow of thought thing that follows)

The magnecor wires hold up a LOT better than the recent Bosch plug wires...
I assume you have replaced them and/or at least tested them.

If you are stinky rich your plugs should be coal black...
Marshmallow white insulator is only OK if they are basically new, tan is a good color.

I like the NGK triples, ~same as Bosch W7DTCs, only less expensive and actually available.
(I get mine at Oreillys) but they require a good ignition...

If you lean the AFM and it runs worse then you were too lean to begin with.
Lean misfires dump raw fuel into the CAT... Stinky?
Misfires will also make the O2 sensor "see" dead lean, as there is way too much free O2.

Starter fluid/propane etc enriches the mixture.
Won't do jack unless you are lean to begin with.

Try shots of brake cleaner.
Hold you breath and stand upwind, only try outside in a breeze.
It will slow or stall the engine if you find a leak
(and you if you get a lungful of the resulting exhaust after going through the engine)

That vacuum still seems too low...
Do the 85s have an idle speed control device? (later ones have it hanging off the plenum, 3 wires, gets PWM DC)
...not at home, can't check Bentley.

Idle speed at 950?
All 4 do the same unplugging the injectors? (~same RPM drop?)

Unless the cam is wiped or you are off a tooth on the cam... Not seeing much.

If it has good power underway, that eliminates a few ideas, basically you are fighting mystery low manifold vacuum.

If the O2 sensor is working properly, it should be trying to lean it out once up to temp.
Unplug, check the voltage out. specs should be in the book, ~.7v indicates stoich, they only read accurately at stoich and tell you rich or lean.

Thought--- If you have a mity-vac put a normal idle vacuum on the FPR, plugging the port on the plenum.
(you might be able to borrow one from a FLAPS, the usual buy/return routine they do)
This will only work at idle, will be too lean underway.
You can adjust your fuel pressure and idle mix this way for testing.

You can also check out the O2 sensor at the same time, voltage will change sharply ~14.5:1.

If that cleans it up, then you can concentrate on why the vacuum is low.
Rent an advance timing light (If you don't have one) and check out the vacuum advance operation etc too.

Verify TDC mark. Do not use a pencil...
Easiest way is probably a 3/16"-1/4" rubber rod through the plug hole, will stop the rotation either side of TDC, mark each and TDC is 1/2 way between.

Draftstmans electric eraser refills work, assuming they still make those.

[mattcfish]

I know you have gone through the ignition, but IME 99% of FI problems are actually gimpy ignitions...

(excuse the flow of thought thing that follows)

The magnecor wires hold up a LOT better than the recent Bosch plug wires...
I assume you have replaced them and/or at least tested them

New Bosch wires, coil, Hall control unit, 3 different distributors tried, stock plugs with 2500 miles on them

If you are stinky rich your plugs should be coal black...
Marshmallow white insulator is only OK if they are basically new, tan is a good color

Agreed

If you lean the AFM and it runs worse then you were too lean to begin with.
Lean misfires dump raw fuel into the CAT... Stinky?
Misfires will also make the O2 sensor "see" dead lean, as there is way too much free O2.

No Cat. Smells like fuelly exhaust, though the plugs say lean. Did I mention that enriching the AFM also makes it run worse.

Starter fluid/propane etc enriches the mixture.
Won't do jack unless you are lean to begin with.

Try shots of brake cleaner.
Hold you breath and stand upwind, only try outside in a breeze.
It will slow or stall the engine if you find a leak
(and you if you get a lungful of the resulting exhaust after going through the engine)

I've had the whole intake system on and off a half dozen times, and have resealed and used new hoses, clamps, gaskets etc. using great care to make sure of no leaks.
I even replaced the plenum because the old one was badly dented by a piston and rod. I'll try brake cleaner though

That vacuum still seems too low...
Do the 85s have an idle speed control device? (later ones have it hanging off the plenum, 3 wires, gets PWM DC)
...not at home, can't check Bentley.

Yes the vacuum is too low, should be 15. The last motor had bad idle vacuum too. Yes it has an electronic idle stabilizer that alters timing. I have three of them (one new one) they all produce the same results. The van idles even worse when they are bipassed.

Idle speed at 950?
All 4 do the same unplugging the injectors? (~same RPM drop?)

Yes, and yes

Unless the cam is wiped or you are off a tooth on the cam... Not seeing much.

If it has good power underway, that eliminates a few ideas, basically you are fighting mystery low manifold vacuum.

If the O2 sensor is working properly, it should be trying to lean it out once up to temp.
Unplug, check the voltage out. specs should be in the book, ~.7v indicates stoich, they only read accurately at stoich and tell you rich or lean.

Cam is a new 2.1 cam. The old cam was damaged in the engine explosion. Same idle issue with new cam and bottom end. I'll check the o2 reading again.

Thought--- If you have a mity-vac put a normal idle vacuum on the FPR, plugging the port on the plenum.
(you might be able to borrow one from a FLAPS, the usual buy/return routine they do)
This will only work at idle, will be too lean underway.
You can adjust your fuel pressure and idle mix this way for testing.

You can also check out the O2 sensor at the same time, voltage will change sharply ~14.5:1.

If that cleans it up, then you can concentrate on why the vacuum is low.
Rent an advance timing light (If you don't have one) and check out the vacuum advance operation etc too.

Worth a try.

Verify TDC mark. Do not use a pencil...
Easiest way is probably a 3/16"-1/4" rubber rod through the plug hole, will stop the rotation either side of TDC, mark each and TDC is 1/2 way between.

Draftstmans electric eraser refills work, assuming they still make those.

TDC was verified on the engine stand when I put the new heads on.

Thanks for the ideas.

[Piledriver]

....
Print up a degree wheel and find a dial indicator then...

[mattcfish]

....
Print up a degree wheel and find a dial indicator then...

Thanks.....2.1 and 1.9 cranks both have the pulley slot in the same spot.... right? I have a 2.1 crank with a 1.9 pulley.
You're theorizing that valve timing is off.... The new cam was installed with the bottom end by Northwest Connecting Rod in Seattle (a very reputable rebuilder).
It seems doubtful to me that they would put a cam in a tooth off. It seems even more unlikely that the cam on the previous engine was also installed incorrectly..producing the same symptoms.

What do you think of the current ignition advance on my
Digijet. 10BTDC instead of 5ATDC. The total advance of a Digijet is about 41 (16 vacuum + 25 mechanical). Right now my full advance is about 50 instead of the stock 36...am I asking for trouble. It isn't pinging, that I can tell.

[mattcfish]

I worked on it again last night. I wanted to totally rule out any vacuum leaks. I disconnected all the vacuum hoses from the manifold (except the one to the FPR and vacuum can) and plugged the holes. I also plugged, the hole where the hose from the auxilary air valve plugs in ahead of the Throttle body. I also disconnected the crank case breather hose and plugged off the hole to the boot. I connected a vaccuum gauge in line to the FPR. When I fired it up the idle did not change much and the manifold vacuum remained low. When I reconnected the hoses one by one the only thing that changed the idle at all was the crank case breather. This was to be expected of course and the change was not drastic. The vacuum stayed relatively even. I then played with the timing a little until I reached my highest vacuum reading with out causing the timing to advance beyond 6 BTDC (if I went beyond 6 the vacuum would continue to rise, but full advance would now be in the melt down zone). By screwing the idle speed screw in after each timing adjustment I was able to get a steady vacuum reading of 10 to 11. Not great, but much better than 8 and 9. The idle is still lumpy and stinky.
I then did some more wiring checks on the injectors. I was able to confirm that the resistance to each injector is exactly 16 ohms, if you check the resistance at the injector. If you check it at the ECU plug it's 17.7 ohms to each injector. I've got 1.6 to 1.7 ohms resistance to each injector through the wiring. Could that cause my problem?
Not sure about the validity of this, but while it was idling, I grabbed the main harness from the ECU and squeezed it and twisted it several times. The idle vacuum improved to 13-14 and then slowly dropped. I could not make this happen every time, maybe it's just mental telepathy, but it seems like there may be issues in the harness. What would cause equal resistance of 1.7 ohms to each injector, when 4 different wires are used? Is this normal. Am I grasping at straws?

[Piledriver]

You are not grasping at straws, sounds like a thorough step-by step troubleshooting session.

The harnesses are 25 years old... It would be interesting to do some checks with a meter (motor not running) to see exactly what's changing.

Could be there's a bad splice buried in there giving you grief all along, hard to diagnose, and would be consistent across the motor swaps.
Might turn out to be a head slapper and easy to fix.

Worst case scenario, there are a couple folks making very nice repro harnesses out of much better materials than the factory had available back then.

[mattcfish]

You are not grasping at straws, sounds like a thorough step-by step troubleshooting session.

The harnesses are 25 years old... It would be interesting to do some checks with a meter (motor not running) to see exactly what's changing.

Could be there's a bad splice buried in there giving you grief all along, hard to diagnose, and would be consistent across the motor swaps.
Might turn out to be a head slapper and easy to fix.

Worst case scenario, there are a couple folks making very nice repro harnesses out of much better materials than the factory had available back then.

Thanks for the incouragement. I need it. After removing the tan covering over parts of the harness, several of the wires are kinked back upon themselves (not the way I would have done it).
I need to remove the extra resistance to the injectors whether it solves the problem or not. I'll try and improve all grounds back to the plug, all sensor wiring and power supply.
Just for chuckles, who makes the new wiring looms?

[ajdenette]

http://www.kyleautomotivespecialties.com/home he re makes harneses I don't see the 1.9 but i belive he will do them.

[mattcfish]

Thanks for the tip. They do have Digijet.

[Piledriver]

I'n no digijet expert, but I'd be curious what the ECU "sees" for the temp sensor used for warmup, and the temp switch if so equipped.
(check everything from the plug at the ECU)

Digijet is mostly just an "integrated" reimplementation of LJet, so most of the same techniques should apply.

The injector wiring resistance is PROBABLY not a major concern.

The test with the FPR varying pressure with a vacuum hand pump and seeing what richer/leaner mix does is still worthwhile if only to check the O2 sensor + circuit.

[mattcfish]

PD,
I've been through all the fuel pressure tests and ECU plug trouble shooting several times over the years. I'll go through it again of course, I know I've missed something.
I'm betting I can find some bad wires in the harness. At least it gives me hope.