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

[ant7]

Originally Posted by Tippy

Scarceller - I haven't verified everything I posted in the list but they've simply crossed my mind.

Some, I don't have the equipment to test them and am trying to rule out EVERYTHING within my knowledge and abilities before I pay someone else to figure it out.

It's a pride thing I guess....

Hi Tippy,
please excuse my ignorance on the last sugestion, i have only had my 3.2 about a month and should have realised that all the dizi does on this later car is distribute the spark!
Anyway, i realy hope you get it sorted soon.
Anthony.

[Tippy]

Originally Posted by ant7

Hi Tippy,
please excuse my ignorance on the last sugestion, i have only had my 3.2 about a month and should have realised that all the dizi does on this later car is distribute the spark!
Anyway, i realy hope you get it sorted soon.
Anthony.

No problem.

Thanks for the suggestions.

At this point, if anyone has had a weird problem electrical, I am all ears.

Thanks.

[Tippy]

UPDATE:

Still no fixxy.

Have done lots of test since last post.

I put a new crank reference sensor on the "reference" side and no change and then read Lorenfb state that reference is only used on startup.

So, yesterday, I swapped the new sensor to the "speed" side and no change.

I did pull apart my aftermarket FPR and discover the piston that presses on the factory FPR had galling on the pushrod. I sanded it and regreased it and now the idle fuel pressure dropped 5PSI.

I am very confident that my DME is the culprit at this point.

I intend on posting on the first post every single thing I've done to this point for anyones reference in the future.

[chiplynch]

TIPPY: This sounds like a distributor-ignition issue. The surging can be the advance kicking in ..the backfiring can be the system firing when it is not supposed to...

Phillip

[Tippy]

Originally Posted by chiplynch

TIPPY: This sounds like a distributor-ignition issue. The surging can be the advance kicking in ..the backfiring can be the system firing when it is not supposed to...

Phillip

The advance weights and springs are in very good condition. Nice, smooth movement.

I put a new coil, cap, and rotor too.

I heard that the DME has FULL control over advance anyways that the advance weights have NO effect.

Not sure if this is fact, just read that here.....

Thanks.

[LJ851]

^ You are correct Tippy, the dist. does not affect the timing in any way.

[Tippy]

Originally Posted by scarceller

And one more possibility I've seen is a faulty injector! If a injector has a intermittent short or has some of the winding shorted then the resistance for that injector drops near 0ohms, if this happens you loose fueling completely. The DME detects over current and shuts down the injection pulses. I don't suspect this is your issue but it could be worth checking the resistance of each injector. If the car has issues free reving in neutral you could also unplug 1 injector at a time and see if it can free rev, idea is to eliminate each injector in sequence. The injectors are all wired together in parallel so 1 faulty injector can take them all out.

Tested all injectors. Siemens rates at 2.35 ohms and I got 2.5 across the board minus one at 2.7.

All good.

Still gonna give the "new" AFM a check but I doubt it would be the problem since it ran EXACTLY the same as before when I changed it.

[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.....

[Tippy]

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.....

This is my next step. I've tried to follow some traces for breaks to no avail.

Going to someone more knowledgeable than me to look at/repair (DME).....

[Quicksilver]

Originally Posted by Tippy

This is my next step. I've tried to follow some traces for breaks to no avail.

Going to someone more knowledgeable than me to look at/repair (DME).....

I spent 3 evenings with a flashlight and a 12x loupe looking over my DME and I couldn't find any issue. I knew the DME was the problem as I had put it in a friend's car and made it immediately DOA.

Gave it to Loren and he found 12 bad solder connections and delivered it back less then 24 hours later.


That being said the quick test is find someone local and put your DME in their car and see if has the same problem.
- The reason I don't recommend putting their DME in your car as a test is there are some component failures that can damage the DME such as a shorted IAC valve or injector.

[Hendog]

Quite a few years back, some guy posted his first post and it was related to a component change in the ECU. It was a great first post; he should have won an award for the "Best First Post"! I saved it but have since updated my PC. I'll see if I can find it. I still have the old Win98 machine around.

[Hendog]

Hello operator? Yes, I'm calling from my Win98 machine...it's dark down here...Yes I put coal in the burner and filled the boiler with water...I hope my connection lasts long enough...

I found the post I mentioned previously. Check out this post and save it!

motronic idle surge solution

[Tippy]

Thanks!

[Tippy]

Issue is 95% resolved.

I finally put a wideband in from Innovate Motorsports (MTX-L) and did AFR testing.

Low and behold, just as I suspected, the engine is very lean. Starting up cold, it was around 10:1 and quickly (within seconds) got up to 14-15:1 and I was thinking everything was ok.

Then, as the engine got warmer and warmer to the point the oil was warm, it was reading 17-18:1!!!!! Wow!

So, I pulled the intercooler off that is bolted to the AFM (airflow meter), flipped the entire IC and AFM over, and drilled out the "tamper proof" cap.

I then proceeded to turn the screw (3mm allen) all the way clockwise for the richest setting to see what the resulting AFR's would be.

Put it all back together and started it up. At full operating temps, it was reading 14-15:1. Score!

Took it around the block and finally, no bucking, surging, hesitating, cutting-out, etc. right from take off/light load!

It still is not perfect but the car is driveable and drives exactly the way it did before.

Now, I have to figure why it went SOOOO lean and the root cause.

[Joe Bob]

rtowle in post #5 suggested monitoring the exhaust.....you coulda saved all this time by doing that at a shop that had an analyzer.

Just saying.

[Tippy]

Originally Posted by Joe Bob

rtowle in post #5 suggested monitoring the exhaust.....you coulda saved all this time by doing that at a shop that had an analyzer.

Just saying.

Funny, I talked to a well respected shop here in SA and after the owner went through a few things with me, he said he'd put it on either a gas analyzer or check AFR's to see what is going on.

I had to rule out every single thing I could test first.

The biggest benefit I got out of this is I understand the Motronic system better than ever and learned MegaSquirt a whole lot.

[Tippy]

Originally Posted by Tippy

Ok, I spoke with Todd from Protomotive.

Here is some of the things he told me I could try:

1. On the Airflow Meter, turn enrichment screw under the aluminum plug.
.......................

Oh man, I am nervous to tell Todd his first recommendation was right.....................I wasted a lot of that mans valuable time!!!!!!

[Porchcar guy]

CONGRATS..Long time coming but success is always sweet...Good job dude !

[Tippy]

Thanks!

[Tippy]

Back to square one.......

Wired up the Innovate Motorsports MTX-L wideband into the car permanately last night. Temporarily, I only hooked it up to set base idle, I did not drive it to get part throttle readings.

So, this morning, I fired her up and took some readings. I had set the AFM to full rich and it was running at around 12.XX:1. Once I tried to give it gas, it started sputtering like it did in the past. This time, worse than ever.

During this time, I saw the gauge spike to 19-21:1!!!! This guage is so precise that the split second I heard the sputter or backfire, the gauge would display the super lean readings.

This is only during off idle and light load (less than 2000RPMs)

I then proceeded to try and take off in the garage and on the driveway. Same thing, sputtering and backfiring.

The only thing I can think is happening at this point is the AFM is either bad (I got it used off eBay and never tested) or the circuit in the DME for the AFM is going wonky at right off idle.

I may put my original AFM back on and richen it to full to see if it is just lean from either the DME degrading or the whatever else is causing the lean condition.

I am fairly confident it is not the air inlet temp or CHT since it would show lean throughout the range and not spike.