Smokin the DJet, Chasing vacuum leaks Options

[robkammer]

I'm in the process of the startup of a refresh of our 2.0 in the LE. Case was split, new bearings, cam, etc. Head were refreshed, new valves, guides yada. With 120 miles on the clock I was experiencing some pretty hard bucking. Not surprising to me as it's a new engine. Since the Djet is highly dependent on vacuum signals I decided to buy a smoke tester, very cool device!

I have much to sort yet, but the test showed significant leaking at the throttle body shaft holes in the throttle body. I'm sure these were leaking before we pulled the motor, and the car ran fine. My question for the 'Brain Trust' is: does anyone rebuild these TB's? Or is there anything I can do in my shop to minimize the play in the body?

There are a couple other leaks I found, top of the AAR for example. I can handle that either with sealer or replace it with another that I have refreshed.

Any suggestions will be appreciated.
Robbo

[emerygt350]

There are a couple of guys on here that rebuild TBs. I had Mark do mine. Bartlett 914 is the user name I think. However, vacuum leaks will not cause bucking. Is this occuring all the time or just while at cruise? For example feathering the throttle to stay at 60 or 40.

[robkammer]

Thanks for the reply. The bucking was mild during the first 30 mile break in run. After an oil change and valve adjustment check, the next step was a 100 mile drive. around the 90 mile mark it became pretty harsh on mild or moderate accelleration, then on steady cruise. I made it back to the shop at 96.8 miles. Oil change, valves again, all good.
Going to check dwell and timing again on start up but I wanted to see if I had any vacuum issues as well. I found quite a few. CSV, AAR, and the throttle body.

I'll be back at it again today to address the AAR and test the system again without the throttle body mounted. But I would like to have this one re-bushed or whatever process is used to seal the shaft better than it is. There was a lot of smoke belching from the TPS.

Pretty cool device from Autoline Products, less than $100 and easy to use. Smells like my old Lionel trains!

[Fazasport]

Rob = EmeryGT350 is correct, your problem is the TPS. I had the same exact issue with my '76 914. The circuit board in the TPS is worn. I was lucky enough to find a new TPS but they are almost lmpossible to find new. NLA from Bosch. The good news is that a replaceable circuit board is now available and your TPS can be rebuilt. I believe you canR get one from 914 Rubber or AA.

[emerygt350]

Not one hundred percent sure on the TPS but it is the common reason. You may want to check and see if it is set up correctly first and test to see if it's triggering the injectors correctly (key on engine not running, actuate throttle and listen for injector clicks).

Are you having high idle issues? That is really the only thing that vacuum leaks result in.

How is your timing?

[robkammer]

Thanks guys. I feel that I'm good with the TPS. While waiting on the motor, I went through just about all of the pieces parts, including the TPS. Even bought a new board from Rubber but discovered the one on the car was like new, and passed the 20 click test without any issues. The car ran fine as well. The motor work was primarily to fix some of the oil leaks, but as things typically go, I discovered a wasted cam lobe, and had the heads freshened up as well. I did discover that earlier in its life someone made it a 2056. That was a good find
I plan on doing the click test again once I stem some of these vacuum leaks.

[FlacaProductions]

My first thought was TPS as well but if you feel you're good there, bucking as it gets hotter/runs longer - an electrical/ground connection affected by the heat? Maybe check the multi-ground point at the top, rear of the motor?

anything else coming/going when it bucks?

[brant]

Bucking is usually the TPS

Maybe the wire plug has a bad wire in the engine harness?

[Superhawk996]

As a contrarian, bucking is often an ignition / electrical cutout assuming we are talking about the same “bucking” behavior where the engine seems to instantaneously lose a little power and then recovers in milli-seconds. Ie not losing all cylinders for an extended duration (like 1 second or more) but an instantaneous dropout and then an almost instant recovery or surge.

Agree with others that a leaking throttle body doesn’t sound like root cause of your bucking.

[fiacra]

Bill at Sparxwerks can rebuild your TB. He's done a distributor and a fuel pump for my VW, and his work is excellent. I believe he is also on Jeff's list of vendors. My recollection is he charges $250 for this service, but I'm going by memory. The work he has done for me is excellent.

https://www.sparxwerks.com/

[emerygt350]

One thing I have noticed is that when it's a TPS issue, it's a full motor miss, I suspect the bad/unexpected signal from the TPS just stops the injectors on both banks.

A slight buck/miss could be as hawk says, grounds, but also a lean miss. If you have a 2056 you need to make sure your djet has been tuned correctly. If you had a rounded cam and other issues before it may not have mattered, but now that it's tip top I bet it wants much more fuel than before. Has the mps been played with? Is the epoxy plug gone?

[robkammer]

All good info fellas, thanks. All grounds are freshly polished and tight. I'll be starting it again tomorrow afternoon, I need to wait for the sealant to cure that I put on the AAR top. Once I have the TB back on I'll do the click test again just to be sure I didn't muck it up when I cleaned the TB while the engine was out.
I can't speak for the FI being retuned for the bigger jugs, I have no record of that work other than an old Pano classified that states the engine was rebuilt at 100k at AA. (123k currently) They have no records from that era.
But I will say again that it did run very well before I pulled the engine. We've put about 4,000 miles on it since we bought it in 2021.
Sparkworks looks like a good bet, once I get it running well and finished with the break in. If, and when.
Stay tuned, I'll post as I go along. I'm really hoping it's not the distributor. it literally took three of us to put the dist in the engine when it was on the cart. The new AA O-ring was so fat! Not sure how I'll be able to pull it if necessary.
Robbo