"Bucking" when wet -- D-Jet, 1.7L '72

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vwduud
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"Bucking" when wet -- D-Jet, 1.7L '72

Post by vwduud » Wed Feb 02, 2005 7:26 pm

When driving in the rain, after a half an hour or so, the engine will "buck", similiar to the conditions described with a worn TPS. I have read both Brad's and KJell's info (as well as seen the pictures if worn TPS's, with the gold "flakes" causing problems). TPS is new as of ~12,000 miles ago. Engine runs fine when there is no rain.

When it bucks, it acts as if it is cutting off the engine momentarily. This has only happened a few times, as I do not drive it very often in the rain. At first, I suspected another electrical issue, besides the TPS. Although I have a cover on the relay board, the top is cracked, possibly allowing water onto the relay board. There are also a few boots, mainly on a couple of the fuel injector connectors, that are cracked or missing. In all but this last time, it would "cut out" only while cruising (say at 45mph in 5th gear - not accelerating). This was just a quick cut out, just a slight "buck". This last time, it was very noticeable under acceleration in the lower portion of the accelerator pedal. If I accelerated with the pedal beyond this point, the problem lessoned.

Any suggestions? Thanks - Jim

mikey373

Post by mikey373 » Thu Feb 03, 2005 4:56 pm

Check cap and rotor, points..and plug wires. The humidity and moisture can get between already dirty contacts, and cause a cylinder to miss.
I had the same thing happen on my truck, but only when it was raining.
Mike

mikey373

Post by mikey373 » Thu Feb 03, 2005 4:57 pm

Check cap and rotor, points..and plug wires. The humidity and moisture can get between already dirty contacts, and cause a cylinder to miss.
I had the same thing happen on my truck, but only when it was raining.
Mike

mikey373

Post by mikey373 » Thu Feb 03, 2005 4:58 pm

Check cap and rotor, points..and plug wires. The humidity and moisture can get between already dirty contacts, and cause a cylinder to miss.
I had the same thing happen on my truck, but only when it was raining.
Mike

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raygreenwood
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Post by raygreenwood » Thu Feb 03, 2005 8:57 pm

There are several definitions of "bucking" on these cars. The first...related to the "gold flaking"...or metal delamination on the TPS circuit...is actually the rarest....believe it or not. The previous post may actually be very correct. Check your cap and rotor. Also, check all of your connections. D-jet connectors are junk. They are suceptable to moisture worse than any other type, because they are already poor connections due to vibration, and they have poor seals.
The grounds on the center line of the case under the plenum are immediately suspect.
Also, if you the air is very dense with water, it makes your fuel mixture a little off. Another very common cause of bucking is the PCV valve on the 1.7 engine. Its inside of that plastic nipple on the oil breather next to the funnel. Its made as part of that nylon nipple that connects to the 12mm breather hose that goes to the intake plenum.
Also, when it rains...the atmospheric pressure drops considerably. When that happens, the copper diaphram in the MPS flexes further outward...minutely. When that happens, if you have the start of a crack in the plate...it will cause this. Also, if you are running too rich or too l ean in baseline fuel mixture....it can cause this when the fuel mixture changes due to the atmospheric pressure and the flexof the MPS diaphram. Check every connector, check everything for vacuum leaks. Oull a vacuum of about 15" on the MPS and hold for five minutes. If it won't hold..that will be a problem. Ray

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Post by raygreenwood » Thu Feb 03, 2005 8:58 pm

There are several definitions of "bucking" on these cars. The first...related to the "gold flaking"...or metal delamination on the TPS circuit...is actually the rarest....believe it or not. The previous post may actually be very correct. Check your cap and rotor. Also, check all of your connections. D-jet connectors are junk. They are suceptable to moisture worse than any other type, because they are already poor connections due to vibration, and they have poor seals.
The grounds on the center line of the case under the plenum are immediately suspect.
Also, if you the air is very dense with water, it makes your fuel mixture a little off. Another very common cause of bucking is the PCV valve on the 1.7 engine. Its inside of that plastic nipple on the oil breather next to the funnel. Its made as part of that nylon nipple that connects to the 12mm breather hose that goes to the intake plenum.
Also, when it rains...the atmospheric pressure drops considerably. When that happens, the copper diaphram in the MPS flexes further outward...minutely. When that happens, if you have the start of a crack in the plate...it will cause this. Also, if you are running too rich or too l ean in baseline fuel mixture....it can cause this when the fuel mixture changes due to the atmospheric pressure and the flexof the MPS diaphram. Check every connector, check everything for vacuum leaks. Oull a vacuum of about 15" on the MPS and hold for five minutes. If it won't hold..that will be a problem. Ray

mikey373

Post by mikey373 » Fri Feb 04, 2005 2:14 am

sorry about the triple post.....hehehehe

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raygreenwood
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Post by raygreenwood » Fri Feb 04, 2005 3:43 am

Man! what is up with this thing? That happens every once in a while . Its like going to Vegas......did the post...."post"?...or if I flip all the way back and dump my post to check...will I find out I got hosed by the "dealer"? :lol: Ray

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vwduud
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Post by vwduud » Fri May 13, 2005 9:42 pm

I'm still in search of a solution here, although the problem has gone beyond times in the rain. Before I get to that, I will mention that the drip pan in the deck lid was not properly secure, allowing water to dump directly onto the distributor. This was the pre 73 pan, that had three straps that hold it in place. the middle strap had broken allowing a dip in the pan towards the front of the car, allowing the water to exit that way, as opposed through the drain holes. The solution was to replace it with one I had out of a 73 with the ribbed reinforcements. Eveb with the strap fixed, the original pan drooped in between straps.

Since replacing the drip pan, I have had very little wet weather driving. That that I did have has had no problem. Just a few days ago however, on a bright sunny, take the targa top off kinda day, it bucked slightly two times driving home. These bucks were more like the engine was turned "off" for under a second. Just like you flipped the key on and off very quickly. Well, I parked it for a few days, then went out to drive it this morning. It started fine, idled down the driveway fine, then once I got in the street, it just quit - shut off completely. The good news is that it started right back up, so I could easily get it back in the carport.

I will begin diagnosis tomorrow, but wanted to get any theories as to what you might think needs checking. This is a fresh rebuild, with less than 3500 miles on it. The DJet fuel injection is in place and works very well (when its not exhibitting this problem). New Djet parts (as of 5000 miles or so ago) include: fuel injectors, TPS, cylinder head temp sensor, trigger contacts, PCV valve, fuel filter and fuel lines (down the tunnel, and all rubber lines). Ignition is a pertronix points replacement with MSD 6 and MSD coil. The relay plate has been restored/cleaned up, but the wiring harness is original. I do have plans to replace the wiring harness soon.

This problem lends itself to be an intermitent electrical problem. Perhaps in the wet conditions it made it more obvious. When the motor misses, it is a very distinctive "on", then "off", then back "on'. There is no gradual decrease in power, then stopping. It seems very much to be something causing either the ignition or fuel deliver (ecu-injectors) to turn "off" due to an open or short somewhere.

Any places to look first in your experiences?

BTW, I have used Brad Ander's website on the Djet system extensively in getting the Djet set up. His advice has been invaluable in fine tuning this 30+ year old system. I will be going back to that site for more info as well.

Thanks for any thoughts you might have. - Jim

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Bleyseng
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Post by Bleyseng » Sat May 14, 2005 10:34 am

Check your ignition switch as those go bad too. Grounds are always a problems so clean and use dielectric grease to seal them from water. Check and clean the tranny strap, FI grounds, Relay board connections, and the fuse box connections.

Geoff

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Piledriver
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Post by Piledriver » Fri May 20, 2005 7:41 pm

I had a Pertronix die on me like that...
Swap the points back in and see.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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raygreenwood
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Post by raygreenwood » Fri May 20, 2005 8:23 pm

D-jet specific items that cause this...are poor connections at the main ground bundle under the FI plenum,.... poor connection at the CHT,.... dirty trigger points....or trigger points whose gap is too wide between the rubbing blocks (something like .923")....or trigger points whose 3 pin plug is in poor condition, and the copper ground wire in the dizzy between the breaker plates. If it is frayed...it shorts when the vacuum advance unit moves the plate.
The reason I list these variables...is because these are the parts that can cause a dead short....losing all injection or ignition momentarily. Its like someone switching the lightswitch off for a second.

The trigger points plug...when it vibrates...if the female terminals make loose contact...or the wires are frayed...will cause all injection to cease for a split second.
The trigger points may also...when the gap is too wide..expand slightly from heat...causing the same thing depending on how much grease they are riding on.
Poor CHT connections...vibrating...will cause intermitant bucking.
Poor grounds ...cause these are the injector channel grounds...will cause the same thing.

Lastly, make sure the FI system power relay (left hand side of engine compartment...first relay on sedans, on top of the brain in wagons)...has an excellen ground to the body. It should have a brown ground wire coming to the screw that holds the relay. Ray

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Bleyseng
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Post by Bleyseng » Sat May 21, 2005 12:54 am

raygreenwood wrote:.first relay on sedans, on top of the brain in wagons)...has an excellen ground to the body. It should have a brown ground wire coming to the screw that holds the relay. Ray
I have never seen a "Wagon 914" got any pics? There is one the factory made as a prototype.

Geoff

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raygreenwood
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Post by raygreenwood » Mon May 23, 2005 9:32 am

:lol: Sorry...I work on D-jet so much in the 411/412.....I sometimes forget that you are working on a 914. Either way...the fuel system power relay and teh fuel pump relay...must have excellent ground.
But.....would you have bought a wagon version of the 914 if they made it? :shock: :lol: Ray

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Piledriver
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Post by Piledriver » Mon May 23, 2005 11:10 am

raygreenwood wrote:: ...would you have bought a wagon version of the 914 if they made it? :shock: :lol: Ray
Yes. My wife thinks it is anyway. I have carried lumber on mine.
OTOH, she has bought living room sets while shopping--- on a Gold Wing.

I think it would have been best as a 2 seat mini pickup, with a bed in the back.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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