Power Cut Under Load

[whalenlg]

@CarBot
Let's see what I hear from the Carbot and everyone else.

1896 944 Turbo with Everygreen turbo + Lindsey DP wastegate and Lindsey boost controller/

Under high boost (driving up our iconic Highway 9 today), I got a sudden jerk and momentary loss of power in 2nd (maybe 3rd? gear). It came back, but I kept the throttle down and it happened again. Driving with a light throttle made the problem go away.
Not wanting to get stranded in the mountains, I swapped the DME relay and proceeded down later with a light throttle and no incident.

Other clues:
-Last week I had a non start event with a warm engine. Started fine on the 2nd try
-My son noted the same behavior accelerating on the freeway in 5th and while cruising at 70 (yesterday)
-I tried to reproduce it accelerating on the freeway yesterday after my son's experience, but no issue. ran up to 15 psi of boost and nothing unusual happened. I am pretty happy with my current setup as it maxes at 15psi.

So - could it be:
Bad DME relay
Bad Fuel Pump
DME cold solder joints
Overboost cut back

[blueline]

@CarBot
Let's see what I hear from the Carbot and everyone else.

1896 944 Turbo with Everygreen turbo + Lindsey DP wastegate and Lindsey boost controller/

Under high boost (driving up our iconic Highway 9 today), I got a sudden jerk and momentary loss of power in 2nd (maybe 3rd? gear). It came back, but I kept the throttle down and it happened again. Driving with a light throttle made the problem go away.
Not wanting to get stranded in the mountains, I swapped the DME relay and proceeded down later with a light throttle and no incident.

Other clues:
-Last week I had a non start event with a warm engine. Started fine on the 2nd try
-My son noted the same behavior accelerating on the freeway in 5th and while cruising at 70 (yesterday)
-I tried to reproduce it accelerating on the freeway yesterday after my son's experience, but no issue. ran up to 15 psi of boost and nothing unusual happened. I am pretty happy with my current setup as it maxes at 15psi.

So - could it be:
Bad DME relay
Bad Fuel Pump
DME cold solder joints
Overboost cut back

CarBot is still a bit quarantined I think. However, Tom is letting CB out of his sub-forum (near the bottom of the main page) in small steps but I thought he was supposed to be released everywhere if addressed directly, so not sure why no response.

Interestingly, this thread does show a call-out to CB when posting a reply so maybe Tom is tweaking the program a bit?

I could be mistaken, so will get this to @Tom for clarification.

[danmartinic]

So - could it be:
Bad DME relay
Bad Fuel Pump
DME cold solder joints
Overboost cut back

Fuel Pump - Never had intermittent failures on FPs, only outright dying, and only twice in two cars

The intermittent starting and performance issues I've had with bad solder joints

If it sits a lot, I'm sticking to "sitting disease". It's my latest go-to

[danmartinic]

What chip are you running? My A-Tune uses a MAP sensor

I've had the MAP sensor fail causing all kinds of weird issues

[Tom]

CarBot is available in CarBot Corner (subforum) for now. I recently started including CarBot threads in search results and the recent topics list, but for now it can only be called in its own forum below. My plan is to modify the system so that it can be called in any forum -- like this one -- but only by the original poster in a thread. That way, people can't have their threads bot-jacked.

As for your high boost stumble, what did it feel like? Was is a sudden and complete loss of power, or more like the car was bogging/missing/sputtering on high boost?

If more of a sputter/stumble/bog, that's very often a weak ignition -- I'd say 80+% of the time -- cap, rotor, and plugs, with weak/turbo-baked spark plug wires being a frequent overlooked cause. If it drives great on light load, but stumbles exclusively under high load (uphill, lower revs, floored in 4th or 5th, for example), that's a classic and common weak ignition symptom.

If it was a sudden and complete loss of power, and only happens on heavy boost, then overboost protection sounds likely if you are still using the KLR and cycling valve to control boost. How are you getting to 15psi? What chips (DME and KLR) are you using and how is the boost controlled -- cycling valve or boost controller? 15psi can trigger overboost on the stock KLR chip under some (but not all) circumstances -- so even if it doesn't happen every time, the key is whether it ever happens when not on heavy boost. If it sometimes happens when not on heavy boost, then it's probably something else -- thing like scratchy AFM traces, cracked solder joints, frayed injector wires or other harness issues, faulty DME relay, fuel delivery issues, etc. Let us know more about what you are experiencing and we can hone in on it...

[whalenlg]

DME Chip is a 24 pin version of the 1989 Porsche chip (upper half of the 2732 28 pin EPROM copied to 2716 EPROM).
Felt a like a jolt under acceleration - power cut, then surged. Backed off the throttle and then added more throttle and it happened again. More of a brief sputter?
My son did say it happened under boost and also cruising about 70 on the freeway.
Plugs are a year old - rotor/cap/wires are about 5 years old but only about 5k miles.

Cycling valve is disconnected - using LR dp waste gate and manual boost controller. I've never had an overboost reaction - even when I had short bursts that recorded as 22psi.

[Tom]

DME Chip is a 24 pin version of the 1989 Porsche chip (upper half of the 2732 28 pin EPROM copied to 2716 EPROM).
Felt a like a jolt under acceleration - power cut, then surged. Backed off the throttle and then added more throttle and it happened again. More of a brief sputter?
My son did say it happened under boost and also cruising about 70 on the freeway.
Plugs are a year old - rotor/cap/wires are about 5 years old but only about 5k miles.

Cycling valve is disconnected - using LR dp waste gate and manual boost controller. I've never had an overboost reaction - even when I had short bursts that recorded as 22psi.

15psi with a more-efficient-than-stock turbo, while running a stock '89 image, could trigger the DME's overboost protection at times. It's near the limit, so might vary based on how much time you have to spool up boost (uphill, high gear, low revs to start, etc.) and ambient temps, etc. People call it overboost, but it's really triggered by air mass/load. When it hits, the DME shuts off the injectors, so you get a complete and sudden loss of all power, but only briefly. As soon as the load drops below the limit, the injectors come back on. I'd say that's it with confidence except for your son saying it happened while just cruising on the highway. If he was really just at a steady cruise and it cut out, that wouldn't be overboost. However, either way, if you are running 15psi, I'd suggest you deactivate the overboost maps as described here. There's a good chance it will fix your hiccup, but either way would be worthwhile at that boost level.

[whalenlg]

Thanks - will try setting it to ~18 for now.

[Tom]

Thanks - will try setting it to ~18 for now.

Is that a typo? You'd want to turn the boost down if you suspect overboost protection...

[whalenlg]

I meant to set the overboost protection as 18 instead of the current 15 in the firmware