No Power when reaching operating temperature

[Oettingerdiesel]

My 91 stock vanagon is having some trouble any advise would be helpful.

When I start my van it immediately starts if I let it idle in the driveway its fine however once I start driving it say 5-8 minutes it starts loosing power and the throttle is just flat. It does not blow smoke or backfire but it does not go faster than 10-15mph, only by feathering the throttle.If I floor it at this stage it seems to want to kill the engine. If I pull over it doesn't die out but just continues to idle perfectly and even revs perfectly. It seems to only loose this power when warm under load.

Its automatic and I had the transmission rebuild 1 year ago but a but haven't driven it until this past friday because I was still working on the interior. since the transmission rebuilt its only had maybe 10 miles put on it driving it in my neighborhood but never out on public roads until yesterday. I did notice that when I floor it it does not upshift. It does however upshift when you drive "normally". So far I have taken it out three days. and every time it lost power.

I guess im mentioning the transmission because i don't exactly know if this may be the culprit.

fuel filter, fuel pump, afm (good), thermo switches, fuel regulator, injectors spark plugs, cap rotor, are all new. Grounds and vaccum lines all check out out

O2 sensor has been disconnected since I've owned this van.

Im ready to cut the cat off and the exhaust rusted anyway to see if its a clogged cat. Yet even here im suspicious because the cat has been welded underneath making me think the PO already hollowed it out. Any other ideas would really be helpful.

Im very hesitant to think its the vanagon syndrome. It does not reset when you restart the van. It does reset when it sits after waiting 1 hour or so for the engine to cool back down. But once warm start losing power again.

heres some pictures of my vanagon!

[URL=http://s304.photobucket.com/user/rt12/media/IMG_6338_zps69mwuoud.jpg.html]

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Driver Found!

[Wildthings]

Did you do the diagnostic test on the FI system shown in the Bentley. You need to do your reading through the wiring harness from the plug on the ECU. My guess would be the TSII sensor or the wiring to it.

The signal wire for the O2 sensor could still ground out to its sheath even if the O2 sensor is not plugged in.

[Oettingerdiesel]

What if i just delete the entire green wire with the tab termination in the above picture Im assuming the signal wire for the o2? to rule out the self grounding issue. I had a local vw mechanic check the entire FI systems and he said hes not finding any problems. That cost me 500 buxs.
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Driver Found!

[Wildthings]

Once you have done it a few times an electrical diagnostic takes 15-30 minutes, add in a fuel pressure test and that takes maybe 10-20 more.

You can check if the O2 signal wire is grounded in a few minutes. I wouldn't clip it off myself as someday you may be required to hook the O2 sensor back up.

[Howesight]

If you immediately start driving when the engine is stone cold, do you get normal or nearly normal throttle response? The answer to this will give an important clue.

In any case, you need to remove the rubber boot connecting the AFM to the throttle body. These boots tend to crack and admit unmetered air into the intake manifold, so the only positive way to check them is removal. Next, you need to check all the vacuum lines that connect, directly and indirectly, to the intake manifold and correct any leaks. The main lines are the brake booster hose, the idle speed control valve hoses, and the breather hose (to the breather tower).

If there are no leaks, you then need to use the method in the Bentley manifold or the Digifant Pro-Training manual. That manual can be found here:
http://www.vanagonauts.com/files/Vanagon%20Digifant%20Fuel%20Injection%20System.pdf


The problem you describe, being lack of power under load when the engine is warm, is caused directly or indirectly by the Air Flow Meter and/or its circuitry. If there are vacuum leaks, then the AFM is not producing the correct signal to the ECU because of unmetered air. If the wiring between the AFM and the ECU is compromised, the ECU is receiving neither the correct load signal nor the transitional throttle response signal. If the AFM itself is malfunctioning, then it is not supplying the correct signal to the ECU.

I suspect that the reason your vehicle starts and runs with no load is that the cold start fuel mixture enrichment allows smooth running until the engine warms up. The ECU ignores the AFM signal at idle speeds - - but only if the throttle position switch is working and correctly adjusted.

The temperature 2 sensor provides the resistance signal to the ECU telling the ECU what the coolant temperature is. This does 2 things. First, it allows the ECU to switch on the oxygen sensor circuit (more correctly, the lambda system), and it "trims" fuel mixture based on coolant temperature.

The portion of the wiring to the oxygen sensor that uses a co-axial cable can sometimes fail by allowing the inside wire (the signal wire) to have contact with the grounded shielding wire. If this is happening, the engine will not even idle when it is warm. I don't think that is your problem. If the terminal connector that normally connects to your oxygen sensor is disconnected, then the ECU just runs the engine in "open loop" mode, which is based on the fuel map, engine rpm and the AFM signal. Your gas mileage suffers because the base fuel map is a bit on the rich side. When the O2 sensor is connected and operating as designed, it imposes an ongoing adjustment of the Air Fuel Ratio to keep it at an average of 14.7 to 1, which is best for emissions. Without the O2 sensor, the AFR can be way off of that target due to wear in the AFM, vacuum leaks, etc.
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'86 Syncro Westy SVX

[Oettingerdiesel]

[bosstyn]

I think Howesight is on the right track. Reading about your problem instantly made me think it was the AFM too.
I had some issues with mine a while back and had to feather the throttle to keep it running.

I say if you can check out the AFM and the associated hoses, you may find your problem.
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Donquita, 85 Westfalia GL

[ftp2leta]

Fuel pressure first, yes check that cat, temps sender, leave the OS unplug for now.

I have never seen a so drastic AFM problem in 12 years


Ben
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Working with rust, grease, dirt and dust is a sad truth.
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[Wildthings]

[pushkick]

so what did you find out was the problem? i am having the same problem loss of acceleration power after engine warms up.
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i see said the blind man to his deaf dog
i am going to quit smoking and drinking and die a healthy man. gotta laugh
there is no deed to the planet earth
1990 vw automatic camper

[Oettingerdiesel]

sorry for the delay guys. i know how frustrating it is to not hear back from someone you are trying to help.

Spend the entire day off today on the bus. I checked every wire in the engine compartment and also checked all the electrical readings from the computer harness. Checked all my relays and grounds fuses etc.

Everything checked out perfect and was in range except for the throttle switch. When I cleaned up the two adjustable allen screws they where way out and loose. Listened for the click & the right ohm reading and put it back together ready for a spin around the block.

Well first thing i noticed was my slightly hard start issue was solved. I was very motivated at this point. I got about 3 times as far as before but after 22.5 minutes , I was getting the same issue again Lose of power when warm.

I headed back in and checked if the throttle switch bolts had come loose but all was good. I did check my air filter and noticed it was the wrong one. So I just ordered a new one. Maybe it was throwing the AFM out of wack. I know its a long shot.

Also since I've had this van ( never really drove it due to fixing) the O2 sensor was never connected. I ordered a new Bosch one just to complete the original circuit. both this an dthe filter shall be here tomorrow.

I did notice I got 12v reading going to my hall sensor which I thought was high but it seems within spec.

Everything in the larger picture seemed to check out. Im still scratching my head since after all this diagnostics , I didn't find anything concrete.

The last thing I will do later tomorrow is solder in a resistor between the two terminals 2 & 4 I believe on the AFM to rule out the VS possibility.

no good news yet im afraid.
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Driver Found!

[Oettingerdiesel]

So spent the entire morning on the bus. I installed new "fitting" air filter , new O2 sensor Bosch ( that was always bypassed since ive had the bus. ) and welded a small hole in the exhaust pipe shut. I also did the VS capacitor mod. Disconnected the accessory belt from AC condenser as my evap is bad anyway. Also checked all vacuums once more. I was doing my finally inspection to try all my fixes and fire up the van when while looking around I put my hand on the breather tower and it moved. I checked the four 10 mm bolts all tight ..... the entire base was cracked open around the perimeter of the tower base and upon removal found that the PO seemed to have patched it horribly with goops of silicone. I cleaned it sanded it and used some german Stabil glue. Which is simply amazing. http://iberhobby.com/product_info.php?products_id=499

This stuff gets rock hard and holds. So im hoping I saved the $85.00 plus optional o-ring purchase from GW.

As I am posting this I am waiting for the glue to dry then reinstall and give her a spin. will let you know if i fixed it finally or not.
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Driver Found!

[jakehenes]

That big of an air leak???Need a pic
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Owner and mechanic - riverwest auto.

[Wildthings]

I would suggest finding a replacement breather tower, new or used. I can't image that any glue is going to hold to the plastic of the tower all that well for very long.

[Merian]

I guess we have a new candidate for the 3D printer program...

[Oettingerdiesel]

well the verdict is in. Nothing i have done has fixed the problem.

It seems worse now actually.

Swapped in a fresh fuel filter. and also disconnected j pipe on exhaust to bypass possible clogged cat. Apart from sounding awesome its no better.

Any suggestions would be appreciated.

I dont even know what to attempt anymore. She idles perfectly but as soon as she's under load its all over the place.
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Driver Found!

[Oettingerdiesel]

just out of curiosity. If i put my hand over the airbox inlet opening to cut off airflow. nothing happens it keeps running. Where the heck could it get that much air from?
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Driver Found!

[Zeitgeist 13]

Recently I was having an intermittent low power issue that was entirely random and quite crippling to the whole forward momentum thing. Turns out the used catalytic converter I installed a while back decided to disintegrate its second matrix, which would occlude the outlet to the muffler. A large section of that second matrix had smoothed itself into a ball that would perfectly cover the outlet under certain circumstances. I pulled the cat and broke out the remaining bits of the second matrix, leaving the first intact and functioning. All power has been restored. Who knew they had two separate matrices?
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Casey--

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

[crazyvwvanman]

It looks like some of the wiring is a little hacked. What is the thin black wire that goes up to a screw on the firewall?

Mark

[Oettingerdiesel]