Starts out smooth, then what the buck? Options

[Jesco Reient]

When I first start the car cold for the day. (2056, D-jet, Raby 9590 cam, timing 27 advance @3500) The car has no cold start valve but has not seemed to care. First start it runs smoothly pulls away from the house shifting @ 3500 it acts nicely. After warming up for awhile as the motor reaches 3200 to 3600 it bucks severely then above 3600 it smooths out a bit. Then as it gets warmer the bucking moves down the RPM range to 2600 to 2800 RPM becoming not very drivable. any ideas out there? (IMG:style_emoticons/default/confused24.gif)

[boxsterfan]

When I first start the car cold for the day. (2056, D-jet, Raby 9590 cam, timing 27 advance @3500) The car has no cold start valve but has not seemed to care. First start it runs smoothly pulls away from the house shifting @ 3500 it acts nicely. After warming up for awhile as the motor reaches 3200 to 3600 it bucks severely then above 3600 it smooths out a bit. Then as it gets warmer the bucking moves down the RPM range to 2600 to 2800 RPM becoming not very drivable. any ideas out there? (IMG:style_emoticons/default/confused24.gif)

Could be TPS worn, trigger points on dizzy or fuel pressure/fuel injector related. You running points or electronic ignition?

[Jesco Reient]

Could be TPS worn, trigger points on dizzy or fuel pressure/fuel injector related. You running points or electronic ignition?

Running a Pertronix unit in a stock distributor, I'll check the Fuel pressure @ 3500 RPM, The TPS switch looked good, Just had the injectors cleaned and flowed. That's some good things to look at for a start Thank You.

[boxsterfan]

Also, how about your fuel filter? Clogged?

Or a pinched fuel line up front by the gas tank? Still running original plastic fuel lines in the tunnel or upgraded to SS?

And, as crazy as it may sound, how are all of your electrical grounds? Battery to body and transmission groundstrap are the biggies.

[r_towle]

What is your valve train setup?
Aluminum or chromoly push rods?
Swivel foot or solid adjusters?
Last time you adjusted the valves?

Rich

[rick 918-S]

From the sounds of your last post about going through the entire F.I. and refurbishing the vacuum hoses and electrical connections I would start to suspect fuel delivery. I wonder if the fuel pump is weak. Describe the bucking. is it a miss or a stall?

Miss could be from the spark plug wire interfering with the MAPS. Someplace around here there is some info about keeping the plug wire away from the MAPS as it will cause issues.

Stall could be from weak pump.

[gothspeed]

The above is good advice ..... the only thing I'd add, is maybe the CHT sensor is bad or not getting a good connection.

[Mike Bellis]

What everyone is eluding to here is you have a lean condition. Lack of enough fuel causes bucking. Other things can too but lack of fuel is the most common cause.

[gunny]

I had the same type of issue and after about a year of working on it i installed a wideband A/F meter. Found out I was running very lean and it leaned out so much at about 3700 rpms that it would loose power and buck. I had to adjust my MPS to get it running great with no issues now.

Try unplugging the temp sensor #2 on top of the intake plenum. It will richen it up some. If that helps then you may need some MPS tuning.

[rmital]

The above is good advice ..... the only thing I'd add, is maybe the CHT sensor is bad or not getting a good connection.

(IMG:style_emoticons/default/agree.gif)
Ground the connection from the harness to the CHT and see if there's a change

[914GT]

Maybe try retarding the timing a few degrees and see if it helps. Too much total advance can cause bucking depending on rpms and light engine load.

[r_towle]

Runs good cold, run worse when hot.
Metal expands when heated.
Check our valves.

[rick 918-S]

Runs good cold, run worse when hot.
Metal expands when heated.
Check our valves.

I would agree it is always good to check valves I would think it would be less likely that it would cause a specific RPM range miss or bucking. Fuel delivery or.... (IMG:style_emoticons/default/idea.gif) MAPS is starting to crack.

[Jesco Reient]

Also, how about your fuel filter? Clogged?

Or a pinched fuel line up front by the gas tank? Still running original plastic fuel lines in the tunnel or upgraded to SS?

And, as crazy as it may sound, how are all of your electrical grounds? Battery to body and transmission groundstrap are the biggies.

Thanks again for the input, Original plastic lines replaced by Stainless Steel lines at the beginning of the build, I have checked all the hoses to make sure that they are smooth with no kinking. Secured the correct groundstrap to the transmission during the engine/transmission installation. I have checked the other grounds back through the harness with a Fluke Multimeter.


r_towle
"What is your valve train setup?
Aluminum or chromoly push rods?
Swivel foot or solid adjusters?
Last time you adjusted the valves?"


The valve train set up is comprised of Raby's spring eliminator spacers, Swivel foot adjusters, Chromoly pushrods, and I just adjusted the valves to zero lash prior to the start up last week. the engine has run well except for the bucking since the valaves were adjusted.

rick 918-S
"From the sounds of your last post about going through the entire F.I. and refurbishing the vacuum hoses and electrical connections I would start to suspect fuel delivery. I wonder if the fuel pump is weak. Describe the bucking. is it a miss or a stall?"

Miss could be from the spark plug wire interfering with the MAPS. Someplace around here there is some info about keeping the plug wire away from the MAPS as it will cause issues.

Stall could be from weak pump."

rick, It feels like a plug or plugs laying down, but I'm thinking with my lack of experience with the feel of the D-Jetronic injection an injector laying down could feel similar. I put a fuel pressure gauge on the driver's side fuel rail (a solid 30 PSI @ 3500 RPM) and started the engine and rechecked the timing this afternoon. The timing is now once again verified to be set to 27 degrees @ 3500. I added a new Yellow mark on the fan when the engine is at 0 Degrees TDC, This combined with my computerized timing light with 27 degrees of advance verified the timing was slightly off from yesterday. I am satisfied with the new timing and the car drove a good bit better with a slight stumble at 3400 to 3800 RPM. But still not something I'd hand over to my wife and so go have fun.

gothspeed

"The above is good advice ..... the only thing I'd add, is maybe the CHT sensor is bad or not getting a good connection."


This is next on my check list, in my research today I have found that if I have the 1974 sensor in my 1973 set up it may not act correctly, I have also found out today that there is supposed to be a resistor inline on the 1973 2.0 litre D-Jet cars that I don't have inline. Brad Mayeur has told me it needs to be a 270 Ohm resistor. That and I may attempt to swap in a different distributor and see if the problem stays the same or goes away.

The advice regarding the wideband A/F meter is interesting which one did you use? I can also check the resistance of the different sensors again and make sure they are still in specifications.

The end result is the car was barely drivable today, so I took it for a short test drive, better than yesterday but tomorrow will be a day of rest for the little car.

Thank you all for your input I'll keep you apprised of where it is at.

[rick 918-S]

You may want to re-run a test on your MAPS too just incase it is starting to crack.

[gunny]

http://www.aemelectronics.com/wideband-air...-fuel-gauge-25/

AEM digital Wideband air fuel gage. I also added a vacuum gage so I could monitor the vacuum and A/F mixture while driving under diffrent conditions. took about a week of test drives now car has a lot of power throughout the RPM range.

I also have a LCR meter so I can keep track of the adjustments to the MPS. Small adjustments to the MPS make signifcant changes to the A/F mixture

[Jesco Reient]

Runs good cold, run worse when hot.
Metal expands when heated.
Check our valves.

.... (IMG:style_emoticons/default/idea.gif) MAPS is starting to crack.

I'm in denial on checking that also but might as well, otherwise I'm just lying to myself. The somewhat progressive nature of this has had me thinking about that diaphragm in the back of my head.

[boxsterfan]

http://members.rennlist.com/pbanders/DJetP...tm#troubleshoot

I assume you have been going through the info in this website. It was very helpful me to me when I started out (and still learning D-Jet).

One thing listed here that is relevant to you is:

What:
Engine "bucks" or jerks at steady part-load throttle settings

Check these:
Throttle switch contacts worn
Dirty, worn, or misaligned trigger contacts


Fix with:
Replace throttle switch. See throttle switch section above for more detail. If condition
persists after testing the throttle switch, it may be due to defective or misaligned trigger contact points.


Maybe you could borrow a known good TPS from someone?

[r_towle]

r_towle
"What is your valve train setup?
Aluminum or chromoly push rods?
Swivel foot or solid adjusters?
Last time you adjusted the valves?"


The valve train set up is comprised of Raby's spring eliminator spacers, Swivel foot adjusters, Chromoly pushrods, and I just adjusted the valves to zero lash prior to the start up last week. the engine has run well except for the bucking since the valves were adjusted.

So, there may be a clue here...

just saying.

My 911 did this.
I fixed everything and replace alot of the vacuum, ignition etc.
I adjusted the valves, problem solved.

Loosen them up.
They will just be louder.
They will then close all the way when hot.
This may fix the issue.
You may need to adjust the valves more than a few times to determine the exact setup your specific motor will run correctly at.

Metal is different from your motor to mine.
There is no one answer that works for each motor.
Search google on Chromoly push rods and valve lash adjustments.
Lots of opinions, lots of research.

Summary, at least my summary, is your motor is not the same as any other motor on earth.
Your cylinders, heads, springs, valves, camshaft, and lifters would all produce different expansion results than any of mine.
So your valve adjustment would end up being different than mine.

Loosen them up, let it be loud to see if the bucking problem goes away.
Then walk them back towards a zero lash slowly until you find the sweet spot for your motor.

rich

[rhodyguy]

have you calibrated the tps using a proper plug, jumper wires, and your multlmeter?