Drivability problem solved with new injectors

rpmoore2 · 08-30-2008, 08:36 AM

Hi all,

I have a 81 3.0L in a 77 911S.

Just recently I had a drivability problem where between start up to 2300 RPM under load the car would sound like it was running on half the cylinders, stumble, hesitate and hiccup. Oddly it would clear up on full throttle after around 2300. The car was fine up to the problem a week ago and oddly it started acting up right after putting gas in the car.

So I took it into the shop and the response was I need new Fuel Injectors. One was totally clogged and the others were border line. So we decided to replace all of them.

Anyway I picked up the car that night and well the same problem was still there. So I left the car at the shop and told them to look at it again. Anyway they confirmed that I was right about the stumbling and a little surprised.

So they checked the injectors and 2 were clogged (worst than before). This time they cleaned out the lines, flushed the system and replaced the 2 again.
The shop wasn't sure if it was fuel or just bad injectors. They also adjusted the cold side of the WUR for me to help with the cold start.

I then picked the car up again yesterday and now runs perfectly. The Aux Air Reg is bad according to them so some day I may have to fix that. So the idle is low on cold start.

So is it possible bad fuel could have caused this issue. It happened so suddenly so I am just confused.

So the question is what really happened. Bad fuel, bad new injectors. I have no problem replacing the injectors since they were probably old. Can't the
WUR cause issues with load on the engine and affecting the control pressure.

The fuel filter was replaced around 600 miles ago. I should say the motor was rebuilt by this same shop 600 miles ago also. CIS FI was relatively left untouched on the rebuild.

rpmoore2 · 08-30-2008, 02:26 PM

I spoke too soon. My problem came back. It was running great for just a day or so.

So I have a question - can the WUR (control pressure regulator) be failing. I assume it has a greater purpose than just warming up and increasing the mixture when cold. Does it play a role when you put a load on the engine? My issue really seems to be isolated only when I push off from a standstill. For example if I down shift or accelerate really really gradually, it is fine. Otherwise as soon as I push just a little bit (lugging the motor just a bit) it starts to stumble badly and just sounds like it is running on half the cylinders. After 2500 RPM or so it clears up.

Could my fuel line from the filter be bad causing fuel injectors to clog up again. I can't believe replacing fuel injectors for the 3rd time will solve this issue.

I should mention since my 3.0 L is not original to the car there is a possibility there is no O2 Sensor. It is suppose to be from a '81 911SC.

Also the cold start is fine and idle seems to be relatively smooth. On full throttle the car is fine too. I haven't had any warm start issues.

The car was in the shop for the last 3 days and they said the electrical was fine. I would assume the fuel pressure is fine too since they had the CIS tore apart 2 days in a row.

So what could they be doing to make it work for a day and then fail. I honestly wonder if my fuel line is bad and my injectors keep on getting clogged up.

Thanks

rpmoore2 · 08-30-2008, 05:18 PM

I'm a novice at this so sorry if I'm not clear on things. I'm trying my best.

Actually any load on the engine will cause the engine to stumble even at 4000RPM. If I gradually accelerate at any speed, as I said before, it's okay not perfect. As soon as I push the throttle aggressively or somewhat aggressively it begins its stumbling. I thought the idle was smooth but I would say it is slightly rough. The car never stalls. Cold and warm start is fine. Cold idle even adjusts slightly. Just driving at 60 mph the car is fine too. I really could use some advise. I spent a lot of time reading up on the CIS at http://members.rennlist.com/jimwms/CIS/components/components.html.

I read this on this web site "On cars with vacuum control, the WUR enriches mixture under load determined by lower intake manifold vacuum." Is there anything else that would adjust the mixture on an engine load. Could I have a vacuum leak somewhere. Would that cause an issue with smoothness under engine stress.

I am going to admit the car is a little more drivable since it went into the shop so I'm glad about that. I'm not sure if I can attribute this to the new injectors or the fact they did raise the idle for me to 1100RPM. I just hope the fuel line is okay and not clogging up the injectors again.

TibetanT · TibetanT's Garage

Well, I'll take a shot since I have some 3.0L engines.

First though, did you by any chance put Ethanol gasoline in your car?

The reason I ask about the Ethanol gas is because that happened to me. Car was running great. I was low on gas so I stopped to get some Ethanol (only gas station open at the time) put a few gallons in the tank.

Drove the car home, about ten miles with no problem. The very next day, the car started fine, drove fine for about 12 miles then started stumbling occasionally. I took the car home and left it over night again.

Next day, started up fine. I drove it four/ five miles and the same thing happened.

Went back home, and did a complete tune-up, oil change and valve adjustment and timing. By now, I had about less than a gallon of Ethanol left in the tank.

Went and got five (5) gallons of Chevron 92 octane. NO PROBLEMS since!!

Also, I thought that the idle that was set by the shop is a little high. Idle speed when timing is set correctly should be in the range of 900 + or - 50.

I hope this helps and I also hope another Pelican with more experience chimes in with their ideas as well.

rpmoore2 · 08-30-2008, 07:17 PM

No I put in 92 Octane gas in the car just before I started having issues last week. I have used this gas station before. We only have 1 station with ethanol in Milwaukee. They do put in 10% ethanol here in the gas.

The car was set up twice by the same shop after that when they replaced the injectors. They also rebuilt the engine and up to now their settings were just fine before my event.

I had a slight oil leak fixed by them at around 500 miles they adjusted the fuel mixture again. This was around 100 miles ago. This was their request as a result of the rebuild.

I am still convinced it is a engine load issue; hence maybe a vacuum leak. Or maybe I don't have an O2 sensor and the fuel mixture on load is not adjusting correctly. Or maybe my injectors are clogged once again for the third time.

rpmoore2 · 08-30-2008, 07:35 PM

Regarding my idle at 1100RPM--- yeah I agree the idle is a touch high. However my stumbling issue was gone yesterday when the idle was that high( after I picked the car up at the shop). At least it was okay for a day. Before I took it in this week it was at around 800 or 900 RPM and I was having the same issue with stumbling.

One reason we chose the higher idle since the 500 mile adj was because of the issue with my AAR which the shop said was bad.

Regardless my cold and warm start seem okay. I was listening to the idle again tonight and it seems fine.

Can I have a theory. I don't want to offend the experts out there since I am a novice.

My 3.0 L motor was retrofited in my '77 911 S without a O2 sensor. As such maybe the load and the vacuum leak depends on the CPR WUR for the right regulation of fuel mixture.

When the shop adjusted the car twice this week I picked it up cold the first time. The WUR worked cold and set the fuel mixture for cold. Failed.

I gave it back to the shop and they adjusted the mixture once again and told me they adjusted the WUR for cold start.

I took the car warm and it worked perfectly just like it did for them.

Now I started it cold this morning and the WUR failed as it did from the beginning.

The question is why did 2 injectors fail for them. That would imply my theory is totally wrong and I have a problem with the fuel clogging my injectors for the 3rd time.

I am so confused why this problem came up suddenly.

shelbypruden · 08-30-2008, 07:56 PM

Run all the gas out and try 87 octane gas, no ethanol. I used 93 octane in my 80sc when I bought it 3 months ago and it drove like hell. Stumbled between 3 and 4k rpms. The factory spec for the my 80 and your 81 engine is 87 octane. Try it. As soon as I went back to 87 octane all my problems were solved.

Shelby

TibetanT · TibetanT's Garage

I'm sorry I cannot be of more help here, but it really does sound like you are getting too much gas...running rich. One way to tell would be to remove the spark plugs and check how they look. Really black, means rich mixture.

But, I am no expert. However, in re-reading your posts here I do have one concern that stuck out and I hate to bring it up. My concern is, if this engine has less than say 1000 miles on a rebuild, then why did you have an oil leak?? Where was the oil leak? Hopefully they told you what it was?

I think you are correct too, that there may be a vacuum leak somewhere in the CIS system. Have you been able to check all the hoses for leaks? There are some really good write-ups on this site with regard to troubleshooting for vacuum leaks and air getting into the system where it should not be...like cracked air box after a bad engine back fire. Do you know if you have a pop-up valve in your air box? If you do have a pop-up valve in the air box then that is not the issue here.

Also, check to make sure your spark plug wires are routed to the correct cylinder. Sometimes that can be problematic as you have mentioned here, but there would be rough running if that was the case from my experience.

rpmoore2 · 08-30-2008, 08:14 PM

I was told to use high octane by the shop because of the high compression from the rebuild. At least I think it was from the rebuild. Asked that specifically at 500 miles when I took it in for the fuel adjustment.

rpmoore2 · 08-30-2008, 08:22 PM

It was a minor leak that the shop took care of for me since they rebuilt the engine. I don't think the current issue is related since the engine was running fine after the oil leak fix.

I would have a small oil drip on the garage floor right after the car sat after being driven. It was running from the back of the engine down to the bottom. The shop was good to take care of it and said it was an odd failure on a new gasket. I haven't seen a drop since.

rpmoore2 · 08-30-2008, 08:24 PM

I was actually going to ask the shop if they put in a pop off valve at the time of the rebuild. So I will follow up with that.

rpmoore2 · 08-30-2008, 08:41 PM

About running rich... Is it possible when the car starts cold and makes the mixture more rich (WUR) that if the part fails it leaves the mixture too rich when warm. Then on engine load the vacuum line from the lower intake connected to the WUR makes the mixture even more richer causing my problem. Sorry for a novice theory. I will check into vacuum leaks however I would assume the shop would have done that too. I still need to confirm if I have an o2 sensor on my retrofited '81 3.0L.

shelbypruden · 08-30-2008, 11:11 PM

My Bad. If it is a high comp rebuild by all means, run high octane gas.

Shelby

rpmoore2 · 08-31-2008, 06:17 AM

Is it feasible to retrofit a 77 CIS system into a 81 3.0L motor? If so, what are the obvious parts to check.

Jim Williams · 09-01-2008, 08:21 AM

Some of the components will transpose. But a big factor is the type of '81 3.0. Is is Euro, or US? If US, are you planning on keeping the O2 system on the '81? What are the details of your rebuild?

There is really not enough information on your engine to answer the question. A simple answer to your first question would be "no".

rpmoore2 · 09-02-2008, 04:23 PM

Well,
I would need some help differentiating a US vs Euro motor. I would bet it's a US version.

I did discuss my engine with the shop today and they said, for the most part, it's a 3.0L without the electrics of the O2 sensor.

So I have a manual set up. I would assume there would have to be a lot of tinkering to keep things running correctly.

Too bad I don't have a Pelican expert as a neighbor.....

I should add things are running better now. The shop thinks my car wash go some engine electrics wet causing my Saturday issue. I drove the car 100 miles this weekend, after the Saturday, and it ran much better. Odd to me....

rpmoore2 · 09-02-2008, 04:42 PM

In terms of the rebuild the crank shaft burned up so it was a bottom up rebuild.
The valve guides were not an issue in this recent rebuild. The car has had a top end rebuild before. A tensioner upgrade was installed at some point. Assuming a '81 motor is suppose to have 8.5:1 compression, then I must have new high compression pistons. Shop says my compression is 10.5:1.

I wish I knew more history on the conversion to 3.0L. I'm sure it would be helpful.

Jim Williams · 09-02-2008, 06:57 PM

The US engine came stock with the Lambda system, and the Euro engine was stock without it. The two engines can be differentiated by the type number. The US engine type number was 930/16, and the Euro engine was a type 930/10. The US CIS had a frequency valve plumbed into the fuel return line from the fuel distributor, while the Euro CIS did not have a frequency valve.

Of course, when engines are modified from stock, no one changes the type number on the engine case to indicate what's inside the engine, so some knowledge of the engine's history is needed. Unless some one has changed the WUR on a US engine when the Lambda system is removed, the engine will never run at it's normal peak capability, as it will have no means to enrich the fuel mixture under load. The US engines depended on the Lambda system to do the enrichment normally done by the WUR on pre-Lambda engines.

rpmoore2 · 09-02-2008, 07:43 PM

Do you know where the markings are on the engine case.

So lets assume I have a modified US version motor and the Lambda system plumbing was removed to make it work in my car. This may be a dumb ? can the WUR from the 2.7 L original to my 77 be installed on a 81 3.0 L to accomendate the lack of a Lambda system. I would then assume there is a vacuum line from the lower intake system to the WUR to adjust the mixture based on engine load. But how would they accomplish this.

I assume I could look at the part number of the WUR and cross check it to a year.

What else could they do. I just assume getting a Euro 3.0 L would be difficult?

Anyway the shop told me specifically I do not have an O2 sensor on the car. So either this US version was converted to make it work using a different WUR or they PO happen to get a EURO motor.

Now I am really interested in getting to the bottom of this.

Thanks for your help

budge96 · 09-02-2008, 08:15 PM

Might sound like a stupid question but are you by some chance running the 2,7US CIS in-
jection on a Euro 3.0 engine?
If so it may stumble and cough and do any number of odd things. If in fact the complete
engine has been installed disregard the question and tell me this is the Lambda sensor
connected? If so disconnect and see how she runs.