Bizarre Behavior Need help diagnosing fuel starvation issue 1989 911

[gad]

Hello,

My father recently purchased a 1989 911 Targa. Had it inspected after purchase, mechanic said, beautiful, well maintained, etc. Dad has been driving around town off and on for the last few weeks, car ran great. He got gas the other day, Cheveron Supreme, and now the car is running horrible. The previous owner had been putting Shell gas in the car.

Could the Techron have loosened particles, etc and maybe clogging up part of the fuel system? Because after putting in the fuel, the car starts fine, but when you push on the gas pedal, it will rev to 1000-2000 and just bounces up and down. Giving it even more gas almost to the floor and it doesnt rev any higher. He tried to drive it, I really cant describe how it ran. For the first few miles it was fine, then all of the sudden the engine would loose power, car would barely run. Car would rev slowly to 2000 (if that), and just bounce up and down, then it will finely catch and the car would take off. It did this the whole way home for about 6 miles.

Not only was it embarrassing, the constant jerking couldnt be good for the engine. So after he made it home, pissed off of course, he siphoned out the Cheveron gas and filled it back up with Shell. The car drove fine after that for about a few trips around the block and then the loss of power, car surging, idle bounce was back.

Any advise would be greatly appreciated. I have spent all night trying to find a solution for him. Thanks for your time

[KFC911]

Welcome to Pelican! I'm sure more knowledgable folks will chime in soon but here's my .02 worth. What you are describing doesn't really sound like a DME relay problem, but I'd suggest purchasing one anyways (around $40) and eliminating it. Every Carrera owner should have a "good" spare one anyways as they are a common cause for leaving folks stranded and they can cause intermittent problems before failing completely. The DME relay (the small rectangular box under the driver's seat) also contains the fuel pump relay, so it "could" be a potential cause for what you're experiencing. Good luck!

[Rot 911]

What you describe sounds a lot like water in the gas.

[msterling]

You've got a "Big Bucking Chicken" in your tank. Sure does sound like water in the gas. Sometimes the Dry Gas treatment will help. A complete fuel system drain and flush may be in order.

Could be the DME relay doing the intermittent thing. Either get a new one or borrow one for a test run. This is a quick and easy plug-it-in test.

[ted]

Agree hopefully just the DME.
But if it is water in the gas be very careful.
Get enough water in the gas and it's possible to hydraulic the motor.

[ChkbookMechanic]

I just had this happen and I couldn't rev my car past 4k. I'd check the fuel pressure - it could need a new fuel pump (which is what I needed).

[88911coupe]

Another one for water in gas since it, per your description, happened right after filling up. There is a drain at the bottom of the tank which will let the water out but you may want to let a mechanic do this since the fuel will come out fast. Change the filter as well since it may be bad it can cause problems that are not really noticable when just idling or low rpms.
Welcome and good luck.

[gad]

Hello again,

I really appreciated the comments.

After talking with Dad this morning, I need to clarify the initial thread.
The problem described didnt happen after the Cheveron gas was added, it started right before. The gas gauge was approx 1/4 or below when the problem initially started. He went to fill up, the problem went away and the returned, and then went away.

He took it to a mechanic who couldnt duplicate the problems Dad described to him, not sure how Dad described the whole situation. So he left the mechanics and drove the car again, no problems, until he let the car go to 1/4 or below again! The same problem started again.

I didnt know it happened the first time a few weeks ago, I thought it started a few days ago. This morning the car started fine, but once again when giving it gas, it will rev to 1000-2000, bounce up and down and really wont go any higher.

Just ordered a fuel filter and DME relay. I will try and flush the fuel system today. I have all weekend to try and find/fix the problem, or its off the shop.

Thanks again for all the help

[Oregon Cab]

Check vacuum lines

[Driver8]

The fuel filter may need to be replaced.

Aaron

[Biff Bradley]

Check the CHT sensor for the updated two wire version.

[Biff Bradley]

Also check that all the ground connections (brown wires) are tight. Bentley manual shows the grounding points.

[gad]

Thanks again for the comments. I will check the mentioned.

I just started the car again and when I was walking around the car, I heard a air hissing noise coming from the front area. At first I thought the tire was punctured, but couldn't find the exact area. Turned off the car and the air noise stopped. Started the car again, the hissing noise started. The exact area is under the front end between the wheels, right around the fuel pump area. Before I get the area exposed, is this noise normal for its area?

[old man neri]

Originally Posted by gad

Thanks again for the comments. I will check the mentioned.

I just started the car again and when I was walking around the car, I heard a air hissing noise coming from the front area. At first I thought the tire was punctured, but couldn't find the exact area. Turned off the car and the air noise stopped. Started the car again, the hissing noise started. The exact area is under the front end between the wheels, right around the fuel pump area. Before I get the area exposed, is this noise normal for its area?

My fuel pump use to hiss, when I took off the skid plate under there it was actually a buzzing sound. It had ran like this for a while. I decided to get a new fuel pump anyways and the sound is gone.

New fuel pump is about $200 and fairly simple to swap out (might be messy though). With a possible fuel problem and a noise coming from the pump it might be a good idea.

[gad]

Well I just removed alot of gas from the tank and then started the car again. Started fine, rev was normal (no bounce, hesitation, etc). I don't know how long that will last, the intermittent problem is confusing.

Ordered a fuel pump, hopefully that helps, if not at least it is new.


Final question for the day, would it be a good idea to run some sort of fuel cleaner now before a new fuel filter and pump are installed?


Thanks again for all the help
Have a great weekend

[robert walsh]

I personally don't use them, if you choose to, do it now, then drain the gas replace the filter and pump. Regardless drain the old gas prior to installing the new parts.

[gad]

Started the car again a few minutes ago, the car would rev to a little over 1000 and then bounce between 1000-1600. So I will buy some manuals this weekend, use the search button, and wait for parts to be delivered.

Besides the fuel filter, fuel pump, and DME relay, are there any other associated parts that could/should be replaced at the same time?

Thanks again for any/all help

[old man neri]

Just curious, but how do you know this is fuel related? There could be a variety of other problems that could cause those symptoms.

Speed sensors, CHT sensor, crank position sensor, loose grounds, solder joints...etc. that may cause such issues.

Will it just not rev past that or is it misfiring? Is it smooth at the said 1600rpm or jerky?

[ischmitz]

It is very hard to do a remote diagnosis but for what it is worth: The DME gets two signals from the throttle body: Idle and wide-open throttle. When the idle contact is engaged (closed) the DME cuts fuel delivery beyond a certain RPM. It is something like 3000. This is to help decelerate the engine when you lift the accelerator. If that contact remains closed when you press the accelerator (bad microswitch) you would notice a similar behavior where you can't get beyond a certain RPM range. In addition the mixure would be off resulting in no power since the DME assumes it is at idle.

But as others said you need to start with the basics: Fuel pressure, fuel filter, fuel pump. Next, the speed and reference sensors can be checked fairly easily. You do need to perform systematic checks, else this can become very frustrating and expensive. Good luck and keep us posted.

Ingo

[gad]

Originally Posted by old man neri

Just curious, but how do you know this is fuel related? There could be a variety of other problems that could cause those symptoms.

Speed sensors, CHT sensor, crank position sensor, loose grounds, solder joints...etc. that may cause such issues.

Will it just not rev past that or is it misfiring? Is it smooth at the said 1600rpm or jerky?

Honestly, I don't know for sure. Wishful thinking that by changing the fuel parts the problem would be fixed, they haven't been changed in a while, if ever. The best thing will be sending the car to the mechanic next week, I am just trying to fix it myself before Dad sends the car in.

I will look at the mentioned sensors and the grounds.

Right now at idle, with light constant pedal pressure, it revs to 1000 and then bounces from 1000 to1600 constantly, it is jerky. Like I am trying to rev the engine with pulsating pedal pressure, but my foot doesn't move and the engine revs by itself. I don't think that makes any sense, with light steady pedal pressure at 1000 rpm (holding at 1000) the engine revs itself to 1600, back to 1000, 1600,1000, etc.

If I push the pedal down further and hold it, engine still bounces and revs itself up and down. Then sometimes it revs fine and I can actually drive the car around the block. But right now, I am afraid to drive the car.

I guess I was hoping for a member here to have had the exact same problem and miracle cure, before the mechanic troubleshoots the problem/solution.