About to run my '87 Carrera off a cliff - still surging and backfiring

[ant7]

hi Tippy,
i realy feel for you with this ongoing issue, one other thing i forgot to ask, does your throttle butterfly shaft have any excessive play in it ? if so, its posible it could be sucking in air at certain throttle positions through the shaft bushings, this leak may or may not be sufficient to cause the issue, its worth checking out though right ?
Anthony.

[Tippy]

TB shaft is pretty tight. I've used 2 large cans of starter fluid all over the intake and vacuum lines with no change to RPM.

[Tippy]

AFR's start out cold at about 12 and climb up to 16-17 at operating temps.

Does the stock C3.2 have this much lean out (range, not 16-17:1 AFR's) to operating temps?

[DRACO A5OG]

That does not look right. Can you borrow a known good AFM?

[brcorp]

Originally Posted by brcorp

Have you checked out you ECU? I had similar problems, turns out there was a broken trace on the ECU along with a couple of bad solder joints - I had Loren rebuild the ECU and it runs as good as new now and that was 5 years ago..... Try swapping the ECU with a similar car. I was fortunate to have someone close who was willing to swap ECUs. Prior to the ECU rebuild we did the swap and then my ran great and his ran like crap. Rebuilt the ECU and problem solved.....

Did you ever check out the ECU??

[Tippy]

DRACO - no I don't have access. Seems like no one in my area has a car like mine or offered to help

brcorp - "ischmitz" tested the DME and it checked ok

[scarceller]

Did you resolve this issue?

[john walker's workshop]

i just put a new coil on a '85 that was doing basically what yours does and it's fixed. the original coil checked out within specs too. bosch coils are out of stock everywhere, but o'reillys has a 23-0280 that is the equivalent.

[H20 LOL]

Coil sounds like a possible culprit. You might as well swap that out to since your throwing parts at it. On the bright side you will have a brand new car by the time your done.

[Tippy]

Coil's brand new.

AFR's now are hitting 18-19 at idle.

Plugged off all vacuum ports, pulled intake to inspect gaskets/insulators and replaced gaskets, tweaked AFR bypass full rich.

Can't figure why it's leaning so much.

Anyone know if the CHT can start reading the heads are too hot leaning the fuel too much? As if it about to die?

That is the ONLY part I've yet to replace.

[Tippy]

Tested the CHT again and it's reading 396 ohms which puts it in the 175* range. I had warmed the oil and shut it off probably 5-10 minutes earlier.

Speccing out fine.

[Tippy]

Took the cover off AFM and started her up. Reached in there and turned the wiper shaft by hand until she read 13-14 AFR.

Magically, she purrs like a kitten.

Half tempted to move the wiper on the shaft to the richer side or take some tension off the spiral spring for the wiper.

[DanielDudley]

Originally Posted by Tippy

Took the cover off AFM and started her up. Reached in there and turned the wiper shaft by hand until she read 13-14 AFR.

Magically, she purrs like a kitten.

Half tempted to move the wiper on the shaft to the richer side or take some tension off the spiral spring for the wiper.

Pretty sure the Ljet system uses a temp sensor to determine how rich to set the mixture. It uses the O2 meter to fine tune it, after the throttle position sensor tell it you are off idle, so this will help compensate for a bad reading at higher RPMs.

[Tippy]

Originally Posted by DanielDudley

Pretty sure the Ljet system uses a temp sensor to determine how rich to set the mixture. It uses the O2 meter to fine tune it, after the throttle position sensor tell it you are off idle, so this will help compensate for a bad reading at higher RPMs.

Mine does not use an oxygen sensor. Both air and head temp sensors spec out to the manual too.

There is no throttle position sensor.

[Tippy]

I am seriously losing my patience with this issue. Not sure if I am going to pull the cam housings off to check cam timing or not.

I couldn't move the wiper on the AFM so I loosened tension on the spiral spring.

It took 4-5 clicks to the loosening side before the AFR's finally fell in place - actually, it is a little rich. Apparently, there are several vids for Toyotas and other makes doing this.

So, I have done these things to richen her up:

1. AFM air bypass screw adjusted full rich (clockwise facing screw)
2. DME Fuel Quality Switch turned 2 clicks clockwise past 0 position which is the richest setting
3. Loosened wiper tension spring 4-5 clicks

But for some reason, it still leans out when taking off from a stop. I mean, going from 14's to 16-17's sometimes 18's in a split-second causing it to cut out. WTF???

Since I can manipulate the AFR's messing with the AFM, I still wonder if my AFM is the issue. I've done many bench test and can never find a bad spot in the linearity of voltage output though.

Anyone willing to part with a KNOWN good unit for testing?

BTW, I blocked all vacuum ports to rule out vacuum leaks. I left the one for the FPR and the vacuum/boost gauge so I could monitor and run the engine in the right configuration for the FPR.

If I don't get this figured soon, there will be a plethora of Motronic parts for sale!

[paulgtr]

take it to a good mechanic. ask some of the pelicans that live near you who they trust. get it sorted. sounds to me like it's not the car but you being stubborn.

[Tippy]

Since you have all the answers, what do I do if the biggest Porsche shop in town won't touch it??

[mepstein]

Go to the smaller Porsche shop that has people who know air cooled engines.

[madkow]

I had this issue 4 years ago. Did you check the Distributor? At the very base of the distributor there are 2 springs that control the advance. You would have to take it apart to see them. If one spring pops out of its position you will have an erratic idle.

[rusnak]

You're way too lean. Maybe you can bump the fuel pressure a bit, or try a custom chip.