Could It Be Plugged Injectors?
 

Hi Gang,

I tried for the third evening to get my car to run smoothly after that mysterious post-engine-wash-rough-running problem. I checked for spark at all cylinders by arcing the plug wire against the engine. I have spark. While the engine is running and I systematically pull plug wires off the plugs, there is an obvious drop in idle with all cylinders but 1 and 6. So, 1 and 6 appear not to be firing. I swithched the plug from 1 with 3 and found that 1 still was not firing. BUT, the odd thing is that the plugs from the non-firing cylinders appear to be DRY! They should be wet with fuel, right? So, do I have spontaneously plugged injectors at cylinders 1 and 6? I have had this problem, on a smaller scale before. It was cleared up by using injector cleaner in a tank and running the car at 4000 RPM on the hwy. Keep in mind, this engine is all new, right down to the spark plug wires and fuel injectors (rebuilt last summer).

How do I pull the injectors to check for fuel flow?

Thanks for any help.

Troy

Start by focusing on what you did prior to problem.

Sounds like you got water in somewhere. How about
the dist. cap?

Check out this website (systemsc.com). It may be helpful.

Good luck
Lorenfb@aol.com

Thanks Lorenfb,

I did check for moisture throughout. I also ran the car a while to heat up and back water out. I am leaning toward plugged injectors because I have spark. Hmmm,

Troy

On one of my cars that was not running right I ended up moving injectors around. I was able to figure out that in my case the injectors were good, the same cylinders were dead. Ended up being two burned exhaust valves.
Hopes this helps

You should do a compression check on those two cylinders that are not firing and a good cylinder to get an idea as to what the compression for your engine is. If the compression is low compare with a good cylinder than you should investigate why the compression is low. Could be a burnt valve like tops911 mentioned or could be you just need to adjust the valve clearance.

I'm interested to see how you make out, I have almost the same problem. I did a compression ck and all are great. I ordered new tune up parts and an o2 sensor (time for replacement anyway), hopefully thet will cure it.

Hey Steve

Do you have a strong spark in those cylinders?

If the compression check is good, and the cylinder doesn't seems to be firing, check the wire, spark plug, rotor and cap.

I don't think the injectors are your problem, but to check them just grab on the nut near the injector and pull straight out. Point the removed injector into a container and crank the engine. You should see a nice spray pattern. If the injector seals are loose, you should replace them before pushing the injectors back in.

You shouldn't have to crank the motor to test an injector that's out. Lift up on the air sensor plate slightly with ignition on, it'll spray.

Start simple!

What kind of spark plugs do you have? Judging from your earlier post, I would start simple and work up. Blow air into your dizzy and make sure it is really dry. Check wire resistance. Even if the plug looks right it could be fouled. Get NGK plugs and ditch the Bosch's of you have them. IF you don't want to run out to the parts store, try swapping the plugs from #2 and #1.

Start the motor and get a water spray bottle and spray a jet onto the exhuast of each cylinder, close to the port. If the water vaporizes, you have heat, right..important to do before the heat fromt he motor is transfered to the suspected cyclinder.

I'm leaning toward fouled plugs...

I had new Bosch plugs in my motor when I made my motor swap..all went well enough, but during the process of tuning the CIS, I managed to foul some plugs. New plugs right? Will it doesn't take much to foul those Bosch plugs. I chased it for weeks, replacing all my fuel components (mostly needed it anyways), even the injectors..might as well right, they are not expensive (less than a few hours' labor charge at the wrench).

put #1 injector in #2, and #2 in #1. same with 5 and 6. leave the fuel lines attached, just swap holes. see if the problem remains on 1 and 6, or follows the injectors. all CIS injectors spray at the same time, so any line can be swapped to any cylinder.

Thanks one and all.

The car ran well Saturday morning for about 15 minutes. It even had full power and reved to 6000 RPM easily, as normal. Then, as I was cruising down the freeway to try and get the fuel injector cleaner through the engine, it began to cut out. It would cut out to a greater extent as I floored it. So, I limped home and checked the fuel injectors for proper spray pattern. They all looked pretty much the same, but showes streams at small deflections of the sensor plate.

Souk, the plugs are NGKs with about 3000 miles on them. They all appeared light brown, impying the mixture is OK. There was some carbon streaking on the insulater of 6 which can indicate a broken plug. I'll look at this closer, but all indications are that I have spark (plugs are dry, and the car runs great sometimes). I did switch a "good cylinder's" plugs for the "bad cylinder" (no. 3 with no. 6) and found that 6 was still not firing, as indicated by listening to the idle change as I disconnected the plug wire from 6. So, I think the ignition is working.

Next I pulled the fuel filter and accumulator. I drained their fuel into a clean white rag and into a glass jar. No filth came from either ( I thougt I might have a catastrophic plug of crud in one of them). All looked OK.

I put the car back together and went for a drive. Again, the car ran great for maybe 20 minutes, and then began cutting out at aggressive throttle applications and higher RPMs (say 4500 and up). So, now the car appears to run OK at a relaxed pace, say up to about 4500 RPM. But, If I do full throttle and RPM runs, the engine stumbles and cuts out until I release the throttle a bit.

It still sounds like a fuel issue to me. Maybe electical/ignition that occurs as temperature increases. I don't know. This is a new problem. Since the rebuild last summer, I have had two episodes of plugged injectors with this car. THe car ran poorly and very rough with the injectors plugged. I put two bottles of injector cleaner in the tank, drive at 4000 RPM, and things clear out and it runs great for a couple of months. This issue I am having feels very much the same as those previous problems.

John, I'll try what you suggest.

From the time of my first post, the car runs much better. It idles normally (I let it idle for 20 minutes in the drive way with no issues) The car is driveable now, just not normal. WEIRD, eh?

Thanks all. I'll keep you posted.

Troy

Re: Could It Be Plugged Injectors?
 

did you install new Beru wires?..........Ron

Hi Noah,
I did the injector check. It appears that "good" cylinders and "bad" cylinders injector's have a similar spray pattern. Nothing dramatically different.

Ronnie, my car came with the stainless shielded wires. I don't have this type on now, but a conventional wire.

Troy

Hmmmm. Well, your injector lines are soft, so pulling injectors and checking spray patterns and volumes is fairly easy. Like Souk says, just turn the ignition key on and lift the sensor plate...they will spray.

Ignition is (or at least used to be) the most persnickity aspect of engines, so just be sure your new wires are working properly. I replaced my wires again this weekend (thanks, JW) and the engine does run more smoothly. Water problems are almost always fixed by COMPLETELY drying the distributor cap and rotor. At high RPMs, ignition should advance roughly 30 degrees beyond idle timing. A fouled plug is still a possibility, and fouled plugs can work fine outside a combustion chamber and not inside (under compression). Spark under compression can be checked with a timing light. There should be no instances of non-flashing.

Fuel filter and fuel tank filter are possibilities also.

I bought a bolt with 17MM head and double nutted it to remove my mesh tank filter, better if you can weld a nut on it (got the tip from a Pelican Tech Article). Cost less than 8 bucks I think.

Have you swapped the injectors and driven the car? Up to 4500RPM???

I would still target the ignition. Everyone seems to blame CIS for their problems, but more times than not, it ends up to be an ignition problem..guess how I learned!

I wonder what would happen if he direct wired the CD box from the starter battery hot to both the constant CD hot and CD trigger on/off.. and a direct chassis ground to the CD box ground wire.. it's probably something I would do IF I wasn't so sure the miss was concentrated on 2 cylinders ..............Ron

Troy,

Was the ambient temp by any chance above 85° F when the missing occured? If so, a bad or intermittent Beru connector is the likely suspect!

I suggest testing the Beru connector separately from the wire by givving it a 'shake test' while connected to an Ohmmeter ... it unscrews ... as suggested in the following thread:

http://forums.pelicanparts.com/showthread.php?s=&threadid=9447&highlight=beru+sha ke+test

Troy,

I know you said you pulled the fuel filter and accumulator and it looked OK, but I would not be surprised if you have a fuel filter problem. I had similar symptoms to yours on my 80 SC. Ran great for the first 10 minutes or so, then cut out real nasty under load. I was a CIS owner since '83 and had learned CIS malady's can take on many forms. Because the CIS is so finnicky about fuel delivery it doesn't take much to make it unhappy. If your fuel filter isn't new, you may wanna put in a new one ---- fixed my problem that sounds just like yours.

I decided the ultimate CIS fix was to drop in a 3.2 DME.

Fast Eddie

Oh! conventional wire means Beru.. sorry to hear about that, LOL

These are good suggestions. I plan on replacing the fuel filter and accumulator right away. I also plan on swapping the injectors to different cylinders to see if the problem with misfire follows the injector. I will also replace the spark plugs and check timing/dwell.

The fuel tank filter is something I had not thought of. I will look at that too.

I don't think the engine has any catastrophic problems like some have suggested because it runs fine sometimes. It feels like it is running out of gas, and then picks up again if I let off on the throttle. The ambient temperature hasn't been over 75 F, unfortunately.

I am also going to have my mechanic, that I use once in a while, do a system pressure check for me to determine if my pump is OK. I was already scheduled to have a CO check anyway.

Thanks all,
Troy

You definitely have a fuel problem, so don't mess with the CD
unit or you may have two problems.

You may have some fuel contamination which ends up at the
problem cylinders' injectors. You should check the fuel pressure
to be on the safe side.

You need to check the spray when the problem occurs as
many have noted in previous posts. Everyone is generally
right on, so focus on their suggestions.

Good luck
Lorenfb
Systemsc.com

Thanks Loren,

I agree. But, while I'm digging around, I will ensure I'm not getting arcing in the plug wires. I also will probably replace the cheap MotorMeister-supplied wires while I'm at it.

I drove the car last night, and it ran OK until I began to exceed 4000 RPM and more than half throttle. When I first started my drive, the car would accept full throttle and 6000 RPM through third gear maybe twice, then it acted like I had depleted a reserve of fuel somewhere. At this point, it would only accept light throttle applications and low revs. I think there may be some restriction in the fuel flow, maybe from the tank? I don't know yet. I'll fine out though!

Thanks again,
Troy

Hmm, could it be a fuel pressure thing? Could the fuel pump have problems once it heats up?

I agree, it sounds as if it is being starved for fuel when you experience the problem. Maybe you can get a fuel pressure guage on there?

Although the 2.7 is a different car...this thread is starting to sound like RazorRacer's thread a while back..but with a twist.

Do you have a vacum guage? Test the vaccum to the distributor/ignition retard when the car is cold, then when the car is warm. It might reveal something...It didn't help me with my ignition problem, but it's a simple test.

I still think this is an ignition problem. If you don't have a vacuum guage or just for grins, try disconnecting and plugging the vacuum line to the dizzy and run the car. I didn't fool around much with my 2.7 motor, so I'm guessing here.

Points. Why hasn't anyone suggested them?! This sounds just like what happens when points start to close. First, the higher rpm driving begins to sputter. At lower rpms (only lightly on the gas) the car seems ok. Eventually, it will start backfiring and sputtering even with light throttle until finally, it won't start anymore. Points closed. See my point?;)
Ryan

You guys are great. I have received a lot of great ideas from the group on this problem.

The fuel pump might be the culprit. I think its original to the car (almost 30 years!) It is quiet when operating though.

The ignition advance idea is a good one. I will check this too. Thanks.

I know, Noah. I've had my troubles over the last year, especially with MM's tranny. They refunded my money on the tranny rebuild though, so I can't complain too much. The new plug wires are from MM and don't appear to be super great. I have had two people look at them and just say "replace 'em". To remind everyone, I did not know the board, or half of what I know now, when I had MM rebuild the motor. In general, the motor is very powerful (compared to stock) and doesn't leak a drop. Still, if I could do the rebuild over, I'd go with Racer's Group, Factory Tour, Caldwell, or someone else (maybe myself), but I can't go back now.

Lastly, I will look at the entire ignition system, including points, over the next two days, if the family will let me in the garage!

Thanks again everybody. Its like the Porche Collective (you know, the Borg) You guys help me be a better Porsche owner and more self reliant.

Troy

Points, points, points, points, points...oh, ok...you can look at them last...if you have to! :D
Ryan

Ryan,

What a GREAT IDEA! I'll do it right away!

Thanks!

Troy!

(how's that, a little more enthusiasm!)

http://www.pelicanparts.com/support/smileys/clap.gif

;)
Ryan

you gotta be kidding.. Why do I assume that people know how to put air in their tires?? .................Ron

Geez Ron, now I have to go check my tire pressures..I was wondering why my suspension felt like it was bottoming out! :D And I just ordered 32 and 45 MM torsion bars for front and rear! :D (JK)

Replace your plugs first. Ngk plugs are smaller than Bosch and don't fit the connector as tight. I had same type of problem. I changed the accum. filter, wires, cap, rotor. ohmed the wires, everything. I didn't change the plugs because they were only 3 weeks old. Changed them and the problem went away.

Troy, check my previous two postings titled "Car backfiring at spec CO level" and "Busy Weekend". For a long time I was having a significant engine hesitation, bucking above 3500 rpm. I was able to make the hesitation go away by setting the fuel/air mixture very rich (CO level above 8%). I knew that something else was wrong and that I was just buying time by setting a high CO level until I could find the root cause. Well, this weekend I used a fuel pressure gauge and determined that my WUR had a clogged filter and was not allowing the fuel pressure to drop (control pressure) to allow the fuel mixture to be enriched when I tried to accelerate. So under acceleration the mixture would be too lean and cause the hesitation. I took the WUR appart and removed the little filter and after re-installing it,and adjusting the CO mixture back to specs, the car now pulls great through all rpms with no hesitation or bucking. BTW you can check if your WUR filter is cloggged by disconnecting the return line from the WUR (not the line from the top of the FD to the WUR) and running the pump (engine off, cold, and disconnect WUR electrical plug) to see if gas comes out of the return line. If it does not, it means that the WUR filter or the return line itself is clogged. As always, one must be very careful with testing involving gasoline. Hope this helps.

Ruben
1976 911 s 2.7L

That's a new one Ruben. Thanks. I will do that test when I'm checking the system pressure, etc.

Craig, the plugs may indeed be the problem. I will replace them as part of this work.

Ronin, I was joking with Ryan. I didn't want him to feel like I was ignoring his suggestions!

Thanks all

Troy

Hi Gang,

Today I found that the WUR is not providing fuel pressure to spec. The pressure is about 1/3 it should be when cold. Then, if I jumper around the relay on the side of the engine compartment, I get a pressure of about 2.9 bar (still about half). So, I possibly have a couple of things going on, a bad or plugged WUR and a power issue.

Also, the system pressure bled to zero in about an hour. Either a bad fuel line check valve or a bad accumulator, right?

Ruben, you nailed it! At least part of my problem is the WUR!

Thanks,

Troy

Any other numbers for pressure? System pressure? Didn't you have a mechanic test those pressures already?

Did someone mention MotorMeister? My whole evening was ruined.
Rebuilt SC motors for $3000. Barrel and piston sets are about $2500
alone.

Please, no more mention of MotorMeister.

Loren

JTO, when I performed the pressure test I looked at two readings. One was system pressure which I tested by using the JC Wittney fuel pressure gauge with the WUR valved off. The other is control pressure which is tested by opening the pressure tester valve and allowing fuel to pass through the WUR. In my case, the system pressure was 93 psi with the valve closed (WUR valved off) and 93 psi with the valve open (WUR in line). This told me that the WUR (or the return line out of the WUR) was clogged. I checked the WUR and that was the culprit with the clogged filter. After removing the filter, and re-testing with the valve open, the control pressure reading was 48 psi. Are you using a pressure gauge setup which allows you to valve off the WUR? If so you need to test for both system pressure and control pressure. Hope this helps.

Hi Ruben,

Where is this filter? I don't want to rip into the WUR with no idea what I'm in for!

Thanks,
Troy

Look at the following site and find the WUR under CIS Components:

http://members.rennlist.com/jimwms/CIS/CIShome.html

My WUR is the 76-77 Model shown. On top there should be two openings for fuel lines, one coming from the Fuel Distributor (FD) and one going back to the gas tank return line. The filter is inside the WUR just below the coupling for the line coming from the FD. I actually pulled the WUR appart and pushed the filter from the inside of the WUR by applying pressure with a thin metal rod through a small opening. I would not remove the filter unless you can verify first that it is clogged. I did this by taking the WUR appart and blowing through the opening which houses the filter. I could not get air to blow through it. Unless I'm wrong (and someone else please chime in) you should be able to test if the filter is clogged by disconnecting the return line leaving the WUR and running the fuel pump (engine off). If gas comes out the return line (need to have a container to collect the gas) then the filter is ok or partially clogged. If no gas comes out, then you have clogged filter. Hope this helps. Best way to check though is to use the pressure gauge and measuring the system and control pressures. Thanks