3.2 Motronic engine running rough backfiring
 

I wish to thank people associated with Pelican Parts for the efforts in service I got during the building of my Project Sixer car. The car was started to day after more than five years of building from the excellent parts at Pelican. Today was a great day!!!!

I do need some more expert advice and guidance since I am getting into the fuel injection which is over my head.

I have been building a 914-Sixer with a 1987 Carrera engine. I know it is not a 911 but I do need the expertise of the 911 crowd. The engine has been setting for about five years during the time I have owned it. The oil was primed by hand and then by starter over a period of a month. The fuel pump was verified in working order by jumping prior to starting without the ECM installed; the same for the coil; found reference sensor was not holding its electrical connection; etc.

The engine has 145,000 miles with excellent compression and leakdown numbers. The compression numbers are140-145 across the board at sea level; leakdown numbers show "0" in four cylinders, 1% in one cylinder, 3% in one cylinder.

It appears that I over serviced the engine and will be having to waite for the excessive oil to burn out. Is this alone enough to cause the engine to run rough, backfire and miss on one bank, appear to run lean, etc????

Or, it this something else such as fuel injectors???

As far as I can tell the injectors have been on the engine a long time and have been sitting without running for considerable time. The oxygen sensor is new along with the rotor, cap, plugs, etc. It appears the engine wants to run occasionally since it appears to run on all six cylinders several times for 30 seconds or so.

In sum, I started the car with starting fluid; got it running rough; I did over fill the oil tank; one bank misfires with flames; engine was taken to 1800-2000rpm; wants to run smooth at times then starts running rough and missing/backfiring.

Definitely over my head on this one. Need advice!!!!

Steve Hurt

Try the "in the Dark Garage and use a spray bottle of Water and mist while car is on" this will determine if you have errand sparks especially at the miss-firing cylinder.

Drain off the oil instead of burning it off

If you have a Cat By Pass on the 3.2, she will back fire.

While sitting did it have old fuel in the lines? If so that may have clogged the injectors. A test, move the injectors around to see if you can cause the miss-fire on another cylinder.

Jim

You may want to consider throwing some BG44K into the fuel system to help rid some contaminates. Make sure it is proper ratio, do not over do it. The Cleaner needs to go through a full tank to be effective.

Check for vacuum leaks as well.

My 2 cents

The reference sensor must send magnetic pulses to the dme or it will misfire. Exactly where are you seeing "flames"? How much did you overfill the oil? Is the motronic in stock form, or modified? Is the fuel pressure regulator vacuum line connected? What was the fuel pressure when you jumpered it? Old gas? Correct 3.2 fuel pump, or a 914 pump?

DRACO A5OG and rusnak:

Thank you for your rapid response. I will try to answer your questions below:

DRACO A5OG:
Oil will be drained off instead of burning off.
Does not have a CAT bypass; running headers through short exhaust mufflers
Engine was not connected to any fuel supply during storage; drained lines and plugged
Will try to move injectors around to see if the problems change
Will use BG44K cleaner into fuel system following exact directions
Will keep checking for vacuum leaks; have not found any thus far.

rusnak:
Reference sensor and speed sensor are both new.
Flames out of one tail/header pipe (911 installation left; 914 installation right side)
Over filled the oil tank by I am guessing 3 quarts; it appears I cannot read the dip stick
Fuel pressure vacuum line??? Will check; this is something new to me.
New gas - Chevron 91 octane
Correct 3.2 fuel pump

I like these suggestions and will also follow them closely.

Thank You very much

My guess is sticky fuel injectors from sitting for 5 years. And remember when reading the oil dipstick the motor needs to be up to temperature and running/idleing.

Thanks, rfuerst911sc.

I am starting to think along the lines of vacuum leaks and sticky fuel injectors. I woke up the morning (4.00 AM) and I think I left one end the line open at an added vacuum gauge. Also, I have the Auxiliary Breather System to add after getting the engine running. I may have left one of these vacuum ports open.

I have drained the tank down below the engine breather line in the tank and also still showing on the dip stick. I will be watching this level to see if I need to take any more oil out.

Is there any way of getting the oil out of the intake/breather system inside the engine other than burning it out???

I am going to try some injector cleaner as suggested but in the long run I think I will pull the injectors and send them to a qualified person for cleaning, testing and general reconditioning.
Does anyone have any suggestions on where to send them??

Any and all suggestions/recommendations are greatly appreciated.

Thanks again,
Steve Hurt

Some strange comments. Be sure you are using an oil tank meant for a 914-6 with a properly calibrated dipstick. Get the whole engine together and vacuum leaks fixed before attempting to start the motor.

are we absolutely sure the spark plug wires are hooked up properly?

Ok, here we go.

I am using a 911 1987 Carrera oil tank so the fittings etc are made for the 3.2 engine I am using. Fact came from same engine; there was considerable oil in the intake breather area and out the tail pipe. Plugged the vacuum to the vacuum gauge and started car. The roughness and missing went away after running for five minutes. It was still backfiring on the one bank; let the car run longer and backfiring appears to have gone away. smoke from the oil has been substantially reduced with very little coming out of the tail pipes. Engine sounds strong but still needs to be run to clear out the oil

The two problems appear to have been the vacuum leak and the over servicing of oil. I am still going to pull the injectors and sent them for cleaning, testing, etc. I thought I had all the vacuum leaks plugged before starting, but by starting i found one along with the oil over servicing. The suggestions made on this thread will be checked individually to make sure the car does not have any problems.

Thanks everyone for the comments and suggestions. It put me on the right track to get the engine running.

I have the entire 1987 Carrera engine, oil system, front oil cooler with fans, etc being used on this car. Car is running headers with M&K short mufflers. The fuel pump, DME, altitude sensor, harness, DME/fuel pump relay, etc came with the engine.

Just a shot, but mine would have muffled backfires/gurgling on deceleration - I thought it was normal, until I found/fixed an ICV (return path xsistors on DME) problem, now they're no where as near frequent/pronounced.

Here are a couple of places for injector cleaning. I used Witchhunter. Ken

RC Fuel Injection

WitchHunter Performance - Injector Cleaning & Flow Testing Services

not an attempt to steal the thread, but I'd like to know more about how your problem was solved.

I agree with Kidrock, I also would like to know more about your problem and how it was solved. This looks very interesting.

Steve Hurt

me 3

also...

I dont think it is resolved yet... this is a new thread.. but I too am watching :p

As for the OP's problem, I think it would be good to borrow a stock 3.2 911, and observe the original fuel hoses, vacuum hoses, and learn how the system works. Sounds like the fuel pressure is not equalized from left to right.

Sorry I'm 'late' - I didn't come back until now. If your ICV vibrates, this may not be the problem.

I only owned the car a couple of years and was convinced of a cold start issue. I worked a lot of things (vac lines, injectors, etc) with no luck / eliminated CHT as a prob etc. I had no idea what the ICV vibe was supposed to feel like - figured it was muffled by the engine vibe. I tested the +12v to it and it was ok, but looking at the schematic I found that the ground is switched. (+12 had no place to return to).

So I made up a fake ICV coil (load resistor) and looked for a signal and one side was missing indicating no drive to the ICV. So it was either stuck in one position or the other all of the time.

I found a thread that helped, and started my own thread, but interest seemed nil, so I never updated it. I post both threads here, and can provide more info if Steve thinks it's helpful.
One transistor needed to be replaced.

Let me know if you want and I will fill in the blanks on my thread or PM me.

HTH

landwerlen's
http://forums.pelicanparts.com/porsche-911-technical-forum/346667-motronic-idle-surge-solution.html


mine
http://forums.pelicanparts.com/porsche-911-technical-forum/573245-3-2-cold-start-issues.html

Damn Dan,

That is Awsome, will to talk my DME friend about this.

Wow,

Jim

Thanks Jim - but I'd be lyin' if I thought that this is Steve's (only) issue - I never had flames, and all my stuff was stock to begin with. BTW I replaced both original transistors as a precaution. My icv certainly vibes now. I'll shutup now :-)