Oddball I4 starting problem--long

[Californio]

I'm at my wit's end with this. No one on the Tiico group site, helpful and knowledgeable as they are, seems to have a great answer, either. Hopefully there are some I-4 folks here who can help me in my plight.

The symptoms: (1) engine starts but immediately rpm drops way down and often it stalls. Once it stalls, it may not start at all, or will take hundreds of starter revolutions to get going, and then it is rough for a few minutes. (2) When it's running, idle is high (1300 rpm +-), sometimes drops to normal (980). (3) Engine runs pretty well at speed though it misses a bit. (4) Condition is MUCH worse after running a bit. First it will start, then shut it off and it will be harder, and so on until it won't start at all.

What I've done.

Installed new throttle body, reset with Vag-Com
Checked all vacuum including brake booster.
New MAP sensor (vacuum reads normal through VAG-Com, about 350-410 mBar at idle.)
Checked temp sensor with Vag-Com--good
Pulled O2 sensor wire--no difference
New coil, new plugs, new cap, new rotor, new plug wires
Replaced fuel pump regulator with known good.
Listened to fuel pump with stethoscope--it's whirring and I think good, otherwise engine wouldn't run at speed, right?
Hit knock sensor for test, removed plug, no difference.
Pulled hair out.

I know some of this sounds like a vacuum leak, but I have looked high and low for one, resealed and reseated everything, and the MAP sensor shows normal vacuum (with fluctuations due to butterfly valve opening and closing.)

And I don't think a vacuum leak would cause the no-start condition.

What would make an I-4 more difficult to start AFTER IT HAS BEEN STARTED a few times, and get worse from there? (Not dependent on temp, just on whether it's been started or not.)

Thanks for reading.

[danfromsyr]

I certainly understand you don't want more speculation. but that all sounds lit Temp-II (maybe Temp-I) sensor issue to me.. but mine is a Digifant-II from an 89jetta I4 system.

I run w/ my O2 unplugged. haven't had time to revisit and replace the part..

what is your Crank to Ignition timing set at? did the Distributor get bumped or somthing? mine was off from *6 BTDC and not a happy camper..

might have to reset the ECM unit to discharge the flash timing map, we had that problem with a 95 Digifant based Eurovan.
disconnect ALL batteries.. then ground the (+)Pos cable to the Ground(-) cable for a few seconds. this will discharge the timing map and force the ECM to relearn the timing map..
if it works similiar. ours situation was caused by rampant misfiring, caused by hot coolant over the Dist cap and continued hiccuping driving operation. the timing was out of parameters of the map.. and it effected Starting timing.

best luck.
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[Vanagon Nut]

Cleaned ISV?

Do you have a test chart for ECU connector pins to various sensors that you could test harness etc. against? IIRC there's related Tiico stuff in the yahoo group.

Does Vagcom show resistance value of temp II sensor so you can compare it to the temp-resistance chart?

Neil.
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1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Californio]

I hadn't thought of resetting the ECU. Not sure if these Tiico's reset that way, but it's worth a try.

Timing is something I haven't checked yet. No, the distributor hasn't been touched.

I don't think it's a temp sensor. I can watch the temps rise on my Vag-Com software screen, and just when it hits around 89, the fan kicks on and it goes down to 86 or so. That tells me the temp sensor is doing its job and giving correct readings through the ECU.

Speculation welcome! At this point I have no ideas of my own.

[Californio]

These Tiico engines don't have ISV's.

Yes, there is a pin connector chart on the Yahoo Tiico site. Since the Vag-Com is showing good readings for the MAP sensor, coolant temp sensor, air temp sensor, throttle body angle, rpm, etc., I'm pretty sure the pins are all working ok.

What I am not getting is why starting the engine a few times makes it really hard to start again. Never heard of anything like this. The wonky idle could be vacuum leak or any number of things. But what is happening after I start it that makes it not want to start again? It's not temperature related--if it's stone cold and I start it half a doesn't times within a minute or two, it does the same thing--no start. Crazy.

[MidwestDrifter]

Since you seem to have covered all the electronic causes. (minus replacing the ecu)

Have you put a fuel pressure gauge on it and watched the pressure during these episodes? You mentioned your regulator is good. But maybe you have an intermittent blockage? Or a bad connection in the power wiring?

I had an engine that got a piece of goose down in the fuel pump intake. It would intermittently starve the pump for fuel. Very tough to diagnose.
_________________
2004 Dodge/Mercedes Sprinter (Custom Camper)
2000 Jetta TDI
1982 Diesel Westy W/ ABA I4 hybrid (Sold)
Epic Road Tripping since 08/05/12 | http://VagariesAbound.blogspot.com/
My Current Build | http://sprinter-source.com/forum/showthread.php?t=41215

[Californio]

No, I haven't done much more on the fuel end than replace the regulator. These engines don't have the tees for checking fuel pressure like the WBX engines, so I'd have to install some kind of tee to read it. That does seem like a logical next step.

This is an 87 Syncro that just turned over 350,000 miles, so it wouldn't surprise me if there was all kinds of crap in the tank and maybe coming through. There's no filter before the pump, either, only after--I replaced that one to no effect a couple days ago, and there was nothing terrible looking in the old one when I drained it.

[MidwestDrifter]

IIRC those pumps have an inlet screen that can be seen through the inlet port. If you have the pump off might be worth it to shine a light in there.
_________________
2004 Dodge/Mercedes Sprinter (Custom Camper)
2000 Jetta TDI
1982 Diesel Westy W/ ABA I4 hybrid (Sold)
Epic Road Tripping since 08/05/12 | http://VagariesAbound.blogspot.com/
My Current Build | http://sprinter-source.com/forum/showthread.php?t=41215

[Vanagon Nut]

[syncrodan]

I second the injector idea, seems like a quick check to pull them and check the spray pattern. A bad injector would soak the plug and cause what you're describing, it's a long shot but it's free and easy. Insufficient fuel pressure would also create a poor spray pattern

[MidwestDrifter]

[Californio]

Yes, the injectors are all on a common rail, and I'm pretty sure you have to pull the intake manifold to get to them.

It could be a bad injector, but the engine doesn't have that many miles on it, and I'm constantly running fuel system cleaner through there.

Tomorrow I'm going to devote some serious effort to the fuel pump and relay.

I don't think this is going to be a relay because the symptoms are constant--no start after a few times running--and this doesn't make sense with a bad relay.

I have a spare fuel pump I'm going to put in, see what happens. If that's it, probably install a filter before the pump (where they should be) to keep all the crud out of the pump of this 350,000 mile/26 year old car.

On the fuel pump regulator, there's a third outlet that appears designed for a gauge. That will be the next step after putting the new fuel pump in.