About to run my '87 Carrera (w/turbo) off a cliff - still surging and backfiring
 

So, I replaced the Idle Microswitch and now an Ariflow Meter. The car still backfires, hesitates, surges around 2000RPM or lower - especially when taking off from a stop.

Idle switch test - wasn't getting continuity at the DME harness plug pin, but was on the WOT switch

Airflow Meter was not gaining voltage in the first 5-10 degrees, then about a .3 or .4 jump in voltage.

Both I obviously thought were the problem.

My multi-meter testing was not fruitful!

Results though, at the DME harness is that every sensor is testing within ohm range or continuity.

My car has a Protomotive chip for the turbo, the only mod done to the DME.

So, ischmitz, Loren, Wong, or anyone else, is it time to tear into the DME?






CR

The ignition box (CDI?) and coil are original from what I can tell.

If this helps......

The distributor came from Craig Garrett "cgarr" and worked just fine after I rebuilt the engine.

Can someone point me to the thread on the DME test and repair?

I need get "knowed up". :)

Brother u find a good cliff let me know. I've been at my 84 for 2 months trying to fix same issues.

Do you have an O2 sensor or some way to monitor your mixture?
If its backfiring alot just off idle, it may be flooding.
How are your fuel pressures on both rails?
Can you monitor the fuel pressure at different load conditions and different RPM's?
Rich

I have a big curb out front...if that works you both can drop those cars over it and I will be glad to catch them at the bottom for you to "help out" :p

Sorry to hear brother! It is frustrating. It is really bad for me since I just rebuilt the engine! I got to the 500 mile mark and this crap started happening.

Rich, the O2 is not hooked up. It doesnt backfire too much, but when it does, it is very loud. I have a 12" long 3.5" inlet/outlet single muffler off the turbo. Fuel pressure is good and raises real quick with throttle movement. I have Defi gauges.

Ed, you already have a fine example. You don't need my money pit!

2nd that on the fuel pressure check.... Had a bmw e30, similar motronic and similar symptoms, was chasing everything u were chasing.. Afm, tps.... Checked the fuel pressure... 25psi. Changed the pump, 90 psi.... Return fuel line was clogged at the tank.....

ingo at 3.6@cox.net can help on the DME.

Fuel pressures are good as monitored by Defi gauges in the car.

What does ingo provide? Schematics, troubleshooting diagrams, repairs, parts?

He rebuilds and repairs DMEs and CDI boxes. Located in Santa Barbara CA.

Will he cough up technical data like schematics and troubleshooting stuff?

I would like to repair myself, just need the data. SmileWavy

He has in the past.....do a search on his name, ischmitz, as well as Lorenfb and earlysman. They have posted schematics.

Ah, thanks! SmileWavy

IF all else fails.... Charlie Jones@Jones Autowerks

Do you mean Bob, or is that his dad?

I have spoke to Bob about this and he's ready to put it on the AFR monitor to start testing but I'm trying to fix it myself. Have to save a little money since I just rebuilt the engine.

Did you try checking the idle air valve?

Yes. If I pinch the hose, the cars starts to die.

"My car has a Protomotive chip for the turbo, the only mod done to the DME."

That's the problem! Your DME ECM/engine is/are NOT stock.
Does the engine really have a turbo? Is so, another problem.
You're wasting time AND money by not focusing on all the mods.
Had a ECM sent in that had the same problem. Once the chip (junk)
was replaced, the engine ran fine. The turbo mods I've seen use
a MAP sensor too.

You also mention a CDI. Did you install an additional ignition system
with the stock ECM.

Bottom line: If really a turbo mod AND a CDI mod, get it back to stock!

Yes, the engine has a turbo (1-bar). No MAP is used.

I put a ? behind the CDI as I wasn't sure if that is proper? The ignition box is stock along with the coil.

That chip may be flooding you.....might consider trying the stock chip to see if it goes away.
A large backfire out of the exhaust may signify a very rich condition at the lower rpms.

From what I have seen and read, which is not a ton, the modifications on these chips seems to be adding fuel at the lower rpms to even out the low end performance.

The upper end of the AF map seems to be pretty good overall, so many just add fuel all the way across the board and that creates rich conditions at various rpms/load/elevation conditions.

might be worth swapping the stock chip back in...its a 15 minute test.

Rich

Well, the car runs very clean and the plugs look brand new with 0 color to them since I installed them 500 miles ago.

I am fairly confident this a lean condition.

But, I know never say never.

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.
2. There is an 8-position switch on the ECU that has different settings for different countries due to different climates, altitudes, and fuel quality. He said each turn was like 5% richer (don't quote me on the exact numbers/%'s!).
3. Last thing is the high-altitude switch that sometimes shorts out and leans the engine 15%!!! It is located by the main harness on the DME and has 2 brown wires? He said disconnect that and it will default back to normal AFR's.

I am definitely going to try #3 when I get home. I've never heard anyone address this one.

Where is the backfire coming from?
Intake or exhaust?

Rich

Exhaust

Typically a backfire in the exhaust is either a loose exhaust that is allowing air in, or a rich mixture.

Rich

Yikes, I would not touch those....they are not common issues with these cars and not symbolic with the problems you've described. Really, if you still have a stock chip, put it back in. It's simple and quick. If you don't have a stock chip, they are relatively easy and cheap to obtain.

Yeah, I don't have a stock chip laying around.....

This is starting to sound more like a seriously complicated and expensive CIS problem that could ultimately end up being a simple ignition problem as is often the case.

Could it be time to start barking up a different tree?




Cheers,

Joe

Brown wire is OK to disconnect under the driver seat.

There was a thread where an ingenious way to check for vacuum leaks, using a rubber glove over the AFM intake and 4-6 lbs of air pressure connected to a vaccum line i.e. cruise control.

+1 items 2 & 3, don't mess with those.

Check the AFR with a LM1 or LM2 or ghetto method, bring her up to 194+ degrees then put a DVM to the O2S and one of the black leads. adjust the AFR screw until your reach .6 volts. That would be close to proper AFR. LM1 or LM2 would be the best tool for this.

Then check and adjust BASE IDLE 880RPMs.

Sorry did not read previous post but regarding the back fires, do you have a Cat Bypass? If so this is a side effect. Mine burps during decel with the M&K Pre-Muff.

Jim

Yes sir. Valves are nearly quiet and it doesn't seem to smell rich at all. I don't have a Cat BTW.

The plugs look really brand new, no soot at all.

Joe, I'm woth you on this. It's one thing if you have a spare chip to throw in, and another if you actually have to start throwing money at a problem you don't really have a handle on.

I was totally confused to begin with....I always thought Turbos were CIS and not Motronic? And, is it really possible to have both at the same time? I know I'm a total rookie, but I've never even seen, read or heard of that before.

- There is no AFM boot, it is all cast aluminum piping for the turbo.
- I don't run an O2 sensor
- There is no catalytic converter, only a short amount of pipe from the turbine of the turbo and a 12", straight through muffler with a 3.5" inlet/outlet leading to a large tip.

Jim, are you referring to the brown "California" wire, or the two brown wires that lead to the High Altitude Switch? Either way, any could be pulled safely....I just thought that there was no way that the altitude switch had any bearing on his problems.

Hold up guys! :) This a factory Motronic, '87 Carrera with a turbo ADDED. Not a '87 911 turbo/930.

Todd at Protomotive said it would make the car 15% leaner. That is huge if so!

That is the first thing I am going to disconnect when I get home.

CR

Oh Damn, check if you can borrow a LM1 or LM2. this is the only way now to check your AFR.

What chip did you have before these symptoms?

Got to verify vacuum leaks. Check shops to see if they have a smoker. That is how I found my leak :eek:

Wait, you have a WUR, right? Like our Base Carrera's Fuel Pressure Regulator?

No WUR, for a Turbo Mod, right?

Yeah, I need and LMX!

The chip has been in there for about 4 years.

I used a whole can of starting fluid and if has vacuum running through it, I sprayed it with NO change to RPM.

I still wonder if the brake booster diaphram could be leaking......

No.

It only has a "rising-rate", fuel pressure regulator over stock.