L-jet help needed Options

[wanchaiwarrior]

74 1.8L L-jet was running well before I decided to give the engine a good cleaning and replace all the old vacuum lines. Now it idles great, but as soon as I go beyond 1/10th throttle it just losses all power. At low throttle it will run all the way to 4,000+RPM. But beyond a certain throttle position, regardless of RPM, it just goes limp.

2 months ago I performed a full tune, including valve adjust, pertronix, plugs, rotor, cap. I have triple checked my vacuum hose connections and electrical connections. I even pulled the throttle body off and checked the TPS operation, which appears to be operating properly. Oddly, my throttle body only has one port that goes to the back side of the vacuum advance diaphragm leaving the port on the front of the vacuum advance open.

It definitely seems to be related to throttle position.

Not sure where to try next. Any suggestions would be greatly appreciated.

[jsayre914]

the port should not be open to air.

check for a nipple along the goose neck rubber where it connects you should find another port open to the air. you are missing a line.

[wanchaiwarrior]

I prepared a detailed diagram before I started disassembly and I'm 99% sure there wasn't a vacuum line there before. I found a diagram over at Pelican that showed the extra line running from the opposite side of the throttle body. My throttle body only has one vacuum port.

[messix]

I prepared a detailed diagram before I started disassembly and I'm 99% sure there wasn't a vacuum line there before. I found a diagram over at Pelican that showed the extra line running from the opposite side of the throttle body. My throttle body only has one vacuum port.

my l=jet doesn't have anything on the advance side either. you good on that. i would check the flapper up at the air box and see if any water got under the cover.could be shorting out the wiper.

[MrKona]

74 1.8L L-jet was running well before I decided to give the engine a good cleaning and replace all the old vacuum lines. Now it idles great, but as soon as I go beyond 1/10th throttle it just losses all power. At low throttle it will run all the way to 4,000+RPM. But beyond a certain throttle position, regardless of RPM, it just goes limp.

2 months ago I performed a full tune, including valve adjust, pertronix, plugs, rotor, cap. I have triple checked my vacuum hose connections and electrical connections. I even pulled the throttle body off and checked the TPS operation, which appears to be operating properly. Oddly, my throttle body only has one port that goes to the back side of the vacuum advance diaphragm leaving the port on the front of the vacuum advance open.

It definitely seems to be related to throttle position.

Not sure where to try next. Any suggestions would be greatly appreciated.

Are you referring to this port?

[wanchaiwarrior]

I actually removed the air box before cleaning, so there shouldn't be any water in there.

Now I've tried with the throttle position sensor connected and disconnected and no difference.

The car runs great under partial throttle and will rev up just fine. To me, that indicates the air box is correctly measuring air volume and delivering fuel. It is only when I add more than partial throttle that the engine literally stops firing. The second I back off the throttle it goes back to normal.

It seems like vacuum, but that would also show up at idle, and it runs absolutely smoothly at idle.

[wanchaiwarrior]

Are you referring to this port?
[/quote]

Yes, that one I have. It connects to the port in the rear of the throttle body. The second one that comes out of the other side of the vacuum advance (on the distributor side) is open.

[computers4kids]

Did you remember to plug the harness back into the airbox?

[wanchaiwarrior]

Did you remember to plug the harness back into the airbox?

Yes. It is connected.

[wanchaiwarrior]

I opened up my air flow sensor and discovered the problem. The center tab connection had somehow twisted to the side and was no longer making contact with the center pole. If you look closely you can see the arrow pointing to the copper tang.

Now the car is running like a top!! I'm so happy (IMG:style_emoticons/default/cheer.gif)

[messix]

thats were i thought you might have had the problem at.

[computers4kids]

Did you remember to plug the harness back into the airbox?

Yes. It is connected.

I see...connected, but not really. Your symptoms sounded way too familar--I've forgotten to plug that connector in once to often. (IMG:style_emoticons/default/smile.gif)

[Cap'n Krusty]

74 1.8L L-jet was running well before I decided to give the engine a good cleaning and replace all the old vacuum lines. Now it idles great, but as soon as I go beyond 1/10th throttle it just losses all power. At low throttle it will run all the way to 4,000+RPM. But beyond a certain throttle position, regardless of RPM, it just goes limp.

2 months ago I performed a full tune, including valve adjust, pertronix, plugs, rotor, cap. I have triple checked my vacuum hose connections and electrical connections. I even pulled the throttle body off and checked the TPS operation, which appears to be operating properly. Oddly, my throttle body only has one port that goes to the back side of the vacuum advance diaphragm leaving the port on the front of the vacuum advance open.

It definitely seems to be related to throttle position.

Not sure where to try next. Any suggestions would be greatly appreciated.

'74s have both an advance port and a retard port on the TB. Actually, '75s do, too. This is NOT debatable. Go look for them.

The Cap'n

[Brando]

To address this issue later on in Motronic cars, Bosch ran a ground wire from the wiper bridge to the wiper. It prevents issues like this from happening.

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.efinnegan.com-2648-1272868011.1.jpg)

More info on AFM rebuilding & diagnostics here.

I opened up my air flow sensor and discovered the problem. The center tab connection had somehow twisted to the side and was no longer making contact with the center pole. If you look closely you can see the arrow pointing to the copper tang.

Now the car is running like a top!! I'm so happy (IMG:style_emoticons/default/cheer.gif)

[charliew]

Nice engineering change to know about. At first to me it looks like the placement of the wire might affect and limit the wiping action but I guess it can be observed and checked. I sure looks like it will cure a intermittent connection.

[wanchaiwarrior]

'74s have both an advance port and a retard port on the TB. Actually, '75s do, too. This is NOT debatable. Go look for them.

The Cap'n
[/quote]

I removed the throttle body yesterday and looked. There is a boss on the opposite side, but it is not drilled. Perhaps this throttle body was replaced with an earlier version by a PO?

[ClayPerrine]

I normally agree with Cap'n Crusty, but on this I don't. Most of the 74s had an advance and a retard port on the throttle body. There were some that only had one. I can't say where the break point is, as all of the throttle bodies I have are off of engines that were out of the cars. I suspect it was very early 74 cars as the throttle body is identical to a 1.7 with the exception of the throttle switch...but I have no proof.

[Drums66]

I'm surprised no 1 told you not to go inside there(AFM)
unless you really know what you are doing!!....it can
be costly! (IMG:style_emoticons/default/huh.gif) (IMG:style_emoticons/default/icon8.gif) (IMG:style_emoticons/default/unsure.gif)

[wanchaiwarrior]

I'm surprised no 1 told you not to go inside there(AFM)
unless you really know what you are doing!!....it can
be costly! (IMG:style_emoticons/default/huh.gif) (IMG:style_emoticons/default/icon8.gif) (IMG:style_emoticons/default/unsure.gif)

I did only as a last resort having exhausted all other options. I've learned through experience that 95% of the time I am able to fix most anything. Most of the time I get it right the first time, occasionally I don't and I pay the price. But the price is usually still less expensive than if I had turned it over to someone else who claims to be an expert.

One thing is certain, if I do screw something up, I only do it once.

[zonedoubt]

More info on AFM rebuilding & diagnostics here.

Great resource. I haven't seen that one before.

I opened up my air flow sensor and discovered the problem. The center tab connection had somehow twisted to the side and was no longer making contact with the center pole. If you look closely you can see the arrow pointing to the copper tang.

Nicely done. I had a problem with one of the other contacts. It was getting snagged on the rotor and would cause the engine to lose power under load.