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Fri Sep 22, 2023 9:59 pm

I’m curious what the cold start cycle is for the Vanagon with fuel injection? I’ve been noticing that a very light throttle inputs when cold, my ‘90 syncro has significant hesitation and kind of pulses. Feels a lot like a misfire. I’ve got a short drive home from the office and for the first 2 miles this happens. It’s pretty much like clockwork, at the same spot it just goes away. It’s about where the temp needle rises just above the thick dead cold bar. I’m assuming this is where it goes from open to closed loop and the O2 sensor is up to temp. There’s no idle issues, no hard start, doesn’t matter what the ambient air temp is, it just happens for the first 5 minutes/2 miles at very light throttle input, then it’s fiine.

From what I could see on searches, most other owners had issues with maintaining an idle on cold start. Can’t seem to find anything with others having this issue. Should I be looking for an air leak or a fueling issue? Or do I just live with it.

Sat Sep 23, 2023 4:12 am

Dump some FI cleaner into the fuel and see if the problem goes away.

Sat Sep 23, 2023 4:30 am

How the engine runs in open loop could be considered the actual state of tune. Once the oxygen sensor comes on line, closed loop, it try’s to compensate for your tune being out of adjustment. In theory a proper tuned engine would not need the oxygen sensor.

So, first test would be to disconnect the oxygen sensor before driving and see if your suspicion is correct.

Next, it’s likely to lean because cold engines need more fuel, so yes small vacuum leaks need to be checked for.

Sat Sep 23, 2023 10:41 am

Had something similar on my 86 sycnro. I solved it , nit saying it’s answer for you, and it might raise argument, but it worked.

Long backstory about my AFM that I won’t get into.

But, last winter and spring I had hesitation and bucking, poor throttle tip in when cold. And even some hesitation when warmed up.

What I did was to adjust the air mix screw in the AFM. I disconnected the idle circuit, the buzzer, and the o2 sensor. I used the o2 signal and multimeter to kinda get a bit of a measure…

Right off the bat the o2 sensor reading was pegged high. I backed out the screw ( they originally have a plug covering the access to the Allen head cap screw).

I had to back out more than I’d thought I would, to get a millivolt readjng from o2 sensor that would bounce between 300 and 800. Did the best I could to get avg reading close to 550-600 or there abouts.

Anyway, was amazed that it actually transformed the engine response . Hesitation gone, throttle tip in smooth. No bucking .

Anyway, it might be something to keep in back of mind if other solutions don’t work out. Keep track of screw adjustment, so you can get back to orig if you have no luck with it.

Cheers

Alistair

my_vw_sucks wrote: I’m curious what the cold start cycle is for the Vanagon with fuel injection? I’ve been noticing that a very light throttle inputs when cold, my ‘90 syncro has significant hesitation and kind of pulses. Feels a lot like a misfire. I’ve got a short drive home from the office and for the first 2 miles this happens. It’s pretty much like clockwork, at the same spot it just goes away. It’s about where the temp needle rises just above the thick dead cold bar. I’m assuming this is where it goes from open to closed loop and the O2 sensor is up to temp. There’s no idle issues, no hard start, doesn’t matter what the ambient air temp is, it just happens for the first 5 minutes/2 miles at very light throttle input, then it’s fiine.

From what I could see on searches, most other owners had issues with maintaining an idle on cold start. Can’t seem to find anything with others having this issue. Should I be looking for an air leak or a fueling issue? Or do I just live with it.

Sat Sep 23, 2023 1:01 pm

MarkWard wrote: How the engine runs in open loop could be considered the actual state of tune. Once the oxygen sensor comes on line, closed loop, it try’s to compensate for your tune being out of adjustment. In theory a proper tuned engine would not need the oxygen sensor.

So, first test would be to disconnect the oxygen sensor before driving and see if your suspicion is correct.

Next, it’s likely to lean because cold engines need more fuel, so yes small vacuum leaks need to be checked for.

Open loop idle is good, light to part throttle is crap, WOT is good. Closed loop everything is great. So it makes sense that the O2 sessor is fixing the short falls of the open loop state of tune. I'll work on cleaning up the fuel system and air delivery.

Thanks for all the help!

Sat Sep 23, 2023 1:09 pm

check for 2.5 bar on the fuel pressure regulator too.