Hesitation Blues - FIXED!!

[Syncronoid]

FYI. AFM was replaced 36k miles ago with a quality refurb from VanCafe.

[E1]

Might be worth it to pop the plug out of the catalytic to discount or confirm a clogged converter.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[tjet]

How old is your fuel pump?

[Syncronoid]

Old. I have a new Bosch I carry at the ready, but I was told by Van Cafe that if it ain't broken, don't fix it. How would this cause hesitation only at low RPMs??

[jberger]

Do you carry a spare ECU? I suspect, if you had a AFR gauge you would see the mixture go flat lean.. an issue with FI pulse width. Swap out the ECU and it will go away. YMMV

J

[Syncronoid]

No spare ECU.

[tjet]

[jberger]

[Syncronoid]

Question remains..... why hesitant only at low RPMs??

[E1]

[Syncronoid]

Could you explain how a bad or clogged Cat can cause my low RPM hsitation symptoms? It idles just fine. And as far as opening up the exhaust upstream from the Cat, do you mean opening the bolt on the release valve of the section of exhaust pipe connected before the Cat? I don't recall seeing a release valve directly on the Cat itself. Thanks!

[E1]

It seems the stock cat we had didn't have a test port, so a smart friend in racing said I'd have to drill a small hole in the cat as a relief valve to see if the cat was shot, and if not to tap and plug the hole or sheet metal screw it if looks aren't everything. I didn't as I wanted a new cat anyway, so bought a Magnaflow. It has a Allen plug on it, but it seems people rotate that to hide it in a rear view. Ours is accessible.

What happens if it clogs much at all then exhaust can't escape. A common test for exhaust leaks you may know of is grabbing a rag and trying to stop exhaust flow at the tailpipe. If you seal it enough it'll die really quickly. Now imagine a clogged converter doing similarly, conditions I described early on include it being *absolutely gutless* under throttle, like it's not getting fuel or has a super-weak spark. Thinking it's slow normally and this feels like having 25 horsepower. You find your right foot escaping through the floor as if wet plugs can't burn fuel.

Hopefully that describes what you have. I'm not convinced of it, but worth a thought -- how old is your converter?

The exhaust port you mention, I think, was for CO testing pre-tailpipe test days but not sure there. I see no reason you couldn't use that for a short time but others here may think that's hard on valves. Defer to them if so.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Syncronoid]

Huh? The big allen plug is where the O2 sensor goes. There's no other port on the Cat. Cat has approx. 65k miles. Exterior condition is fine. When I bang it with a rubber mallet, there is NO sound like pieces of metal rattling inside. Seems solid.

My engine idles fine and has normal power as it accelerates from 2000 to 4000 RPMs and there is no lack of power on the hwy, easily cruises at 70 to 75mph. It's just the 'off the line' acceleration, from 1000 RPMs (idle) to 2000 RPMS where it is sluggish and seems to struggle and cough. As soon as I touch the accelerator, it hesitates and struggles to get the RPM's up. After a couple seconds it starts to rev, the RPM's come up and I'm good to go.

[tjet]

You are asking for help on troubleshooting your current problem. We have made several suggestions on things you can try - free things, like take off your cat, look for vac leaks, & try the new fuel pump that you already have. Now you want us to explain our logic? At best, we are shotgunning ideas to you. Also, just because you installed "x & y" part recently, it doesn't automatically mean it's good.

The proper way to do this is to start with a compression test. Easy enough to do and get it out of the way. Will it fix it? No.

[Syncronoid]

Sorry, I'm not trying to second guess your suggestions, I'm just trying to think them out. The cat, the vacuum leaks, fuel pump and a compression issue are all things I would expect to cause problems at any RPM, from idle to top end (and particularly at idle or top end). My problem seems focused in getting from 1000 to 2000 RPMs.

I'm just a weekend mechanic, I don't have a shop in my garage, I'm just trying to address what I can, without making the van undrivable or breaking something that isn't broken, before taking it across the Bay to Buslab.

[E1]

When our fuel pump was clogged on the inlet end it only ran rough when line pressure was low, like when trying to build speed off the line -- just like the converter issue.

Our cat clog mostly affected trying to get up to speed. Once there and spinning revs it ran much better, as mentioned.

The converter port -- on the Magnaflow, anyway -- can be used for an O2, but on the older buses the O2 port is upstream, in the collector pipe on the driver's side.

As said it may not be the cat, and now that you've quoted 65K miles it should be fine unless a reasonable number of those miles were while it was running rich. We only got 16 months and maybe 15,000 miles out of a brand-new Magnaflow from loading it up with unburned fuel when rich. That must superheat the cat when coated, I think, which breaks it apart inside.

I totally get not wanting to strand oneself with a mechanical error, too,. We live on the road and are spinning wrenches mostly in roadside dirt, often about 100 miles from any town.

Is it possible that your O2 is a single-wire type costing like $18? If it is, and the wire end on the sensor was cut and exposed to attach it to the van wire, it will not function correctly. There's a second wire surrounding the inner wire and if the two touch the O2 will short and work intermittently at best.

There's a lot of things this problem could be in the end, your opening running condition reads differently than the last one, so that makes it harder. Couldn't hurt to double-check that no plug or coil wires have wiggled loose, either.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[Syncronoid]

Thanks for the input.

The O2 sensor is a high quality, no-splice direct fit plug-in version.

[Zeitgeist 13]

I'm anxious to see what you come with for a solution, as I'm experiencing a similar issue with a new 2.1 I'm setting up for a friend. It idles very nice, but bogs down when pulling away from a stop at operating temps. It doesn't do this when cold. It mostly runs great once going, but the power seems to sawtooth (I can't describe it any better) as you accelerate with mid to full throttle. I've felt this sawtooth phenomena on my old 2.1 as well, but to a lesser extent.

It has a new 2.1, ox sensor, full tune kit, adjusted TPS, rebuilt injectors, and I temporarily tried a factory "syndrome" harness--no change. I also stripped and rebuilt the engine harness.

This one has a Triumph Adler ECU.
_________________
Casey--

'89 Bluestar ALH w/12mm Waldo pump, PP764 and GT2052
'01 Weekender --> full camper
y u rune klassik?

[Syncronoid]

Could a bad Temp 2 sensor possibly be causing my problem? i.e. when engine is hot, ECU thinks it's cold and raises fuel/air mixture, perhaps flooding the engine?

How does the ECU adjust fuel/air mixture based on the data from this sensor?
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'90 Syncro Westy w/GW2.5L

[jberger]

I guess I misread your initial description.

A bog off idle can be a mixture issue. On modified engines especially. At idle the FI is bopping along nicely. Open the throttle and the O2 feedback takes a few moments to catch up with what it's seeing. If your initial AFM baseline is not rich enough then that first few moments will be effected by it. I have worked with quite a few modified Digifant engines that needed AFM adjustment to run correctly just off idle.

J