Very Rough, Low Idle and Missing - Help!, 73 D-Jet - SOLVED! Options

[ThinAir]

RRC is only a couple of weeks away and I'm beginning to get desperate that I'm not going to be able to drive my 914.

When I posted this, my problem was just that the idle would hunt, but otherwise it drove well. After reading the responses and reviewing Brad Anders' stuff again it made sense that my hunting problem was probably that I was just running lean. I turned the ECU 3 clicks clockwise to see if that would improve things, but it didn't seem to.

Well, things have gone from poor to bad. Right now I've got a car that barely idles at all, and when I'm accelerating or driving on the highway it often bucks/misfires. I haven't run it long enough to get it warmed up. I've tested the AAR by pulling the supply hose and it seems to be working. If I remove the AAR output hose the RPMs go up to 1000 so perhaps the AAR isn't opening fully.

I've measured the ohms on the CHT at 124 so that's within range, and I've got a brand new 270 ohm resistor inline. I have 3 MPS units that all pass on resistance and vacuum and changing them makes no difference in the behavior. I've also recently replaced the spark plug wires (not to solve this problem, but just because) and I've made sure that they are as far away as possible from the MPS unit. I've also checked every electrical connection that I can find.

Sorry that all that is so long - any clue what I should be looking at? I'm beginning to panic (IMG:style_emoticons/default/blink.gif)

[timothy_nd28]

Have you pulled and inspected your plugs?

[ThinAir]

Have you pulled and inspected your plugs?

That's on the list for tomorrow after work. I got tired of working by light-bulb tonight.

[hot_shoe914]

Check the points to while you are at it.

[DRPHIL914]

Check the points to while you are at it.

(IMG:style_emoticons/default/agree.gif)

the hunting could still be a lean issue , i have had 3 mps that "tested" o.k. but were actually causing a lean running issue- adjusted the MPS and it was gone, but it sounds more like your points or the injector trigger points plate may need replaced or cleaning too. I would check your grounds for the FI harness. mine was loose and acted just like you are describing. i had 3 issues going on - needed new fi harness that i got from jeff bowlsby, new injector trigger points plate, and put new points(later went to petronix) since then i tuned the MPS and the timing an now all is well. --

1- check plugs r they white(too lean,hot), black and sooty(too rich)
2. points dwell and timing - when did you set the valves last?
3. wires and fi grounds ar tight
4. if you have an MPS that the epoxy plug is removed you can adjust this per anders site direction ---- mine took one full turn to be the correct richness and A/F ration (i have a gauge) - - and i had it pre set by a member to be set to factory setting, prior

good luck and keep us posted

[JStroud]

The bucking and misfiring at speed might be the contacts in the TPS, if they're worn might need to move them to a better path and adjust it. Helped on mine with similar problem. Good luck.

Jeff

[ThinAir]

Update: Tonight I pulled all the spark plugs, checked the gap and cleaned them. They weren't fouled, but they were sort of a darkish brown and certainly would benefit from a little treatment with a wire brush.

Once I fired it up, it ran pretty much just like before. I took it out for a drive so that I could get it warmed up. It sputtered and bucked, but after about 10 miles on the freeway it suddenly smoothed out. I drove it another 30 miles at 75 mph, even tested acceleration from 75 to 95 and everything was smooth as can be. Once I got home it was idling smoothly at 900-950 just like I want it.

So I'm pretty sure that this is a cold-engine issue. The proof will come tomorrow morning when I drive it to work. Work is 8 miles on city streets and takes 20 minutes. I've long suspected that this does not work the engine hard enough to truly warm up.

So... this is gonna be a bit long, but let me give you a rundown on this car and the history of the problem I'm trying to solve. There's a question at the end, really!

This car is a 1973 2.0L with stock D-Jet fuel injection. All parts match Brad Anders list of 1973 parts, including the CHT and the home-built 270 ohm inline resistor. I've got Bowlsby ignition and FI wiring harnesses that are 3-4 years old. Battery is in good condition and alternator light does not come on at idle (after recent adjustment of the alternator belt). McMark rebuilt the distributor last summer, including the injector points.

At WCR 2011 I asked McMark to drive my car because I was having a problem with bucking when I went through 15mph school zones in 2nd gear. Otherwise the engine was running wonderfully. He diagnosed a MPS issue, which was proved by swapping the MPS with a known good unit. After I got home I traded for a known good MPS, but once installed I had the same issue. With help from the World community I was able to determine that this was due to the routing of my spark plug wires. I recently changed to 8mm Clewitt plug wires in hopes that it would reduce the chance for interference with the MPS.

I wanted to put my original MPS back in because I just trusted it more, but when I swapped MPSs the engine bucked and would hardly run. Of course this was strange since I'd run that MPS for a long time, but I'm not one to argue with reality so I put the other one back in and the engine went back to running pretty much as I'd like.

Somewhere along the way I noticed that the engine wasn't idling well, and I opened up the throttle bipass to get it to be less annoying, but clearly there was a problem. I started reading through Brad Anders stuff again, particularly his article on stabilizing the idle, and decided to do exactly what he said - check all the basics first, then run the car for 30 minutes on the highway to make sure it was well warmed up before setting the idle. I also turned the ECU knob clockwise by 3 clicks to slighly enrich the idle mixture.

That all went well enough, and I had a warm engine that was idling at 900-950, until I went to back it up to pull into my driveway. For some reason it started sputtering and eventually died, refusing to restart until it had set for several hours. It made me think it had flooded.

Later I had run it again until it was warm in hopes of adjusting the ECU knob to get the idle as smooth as possible. I had moved the battery to get to the ECU knob, and when I moved it back the engine died and would not restart until several hours later. Again, it figured it was flooded.

I noticed that the CHT lead with my home-built resistor was laying across the positive battery cable and had moved when I moved the battery, so this made me suspicious of the CHT resistor and I built a new one. Pelican's site says that a bad CHT sender circuit can result in just the kind of behavior I've been seeing. I try to be careful when handling hoses & wiring, but I'm wondering of something got damaged when I was swapping around MPS unit. I can't see anything and the CHT measures the right resistance, but they can just wear out also. Running this new resistor has made no difference in the rough running.

So I decided that I should have a spare CHT, even if the existing one wasn't bad. Pelican lists one for all years, except 1973, and says the one for 73 is NLA. (I haven't been able to find a 0 280 130 003 anywhere.) GPR lists a 0 280 130 012 unit as being for all 914s so I ordered one of these. Brad Anders makes statements about CHTs in several places that mention conflicting part compatibility and in one place makes it sound like the 0 280 130 012 unit will work with a 73 & 74 2.0L, but with no mention of whether you run it with the 270 ohm resistor or need some other value.

So here's the question (besides, do you have any ideas about what's going on): When the 0 280 130 012 arrives, can I run it in my setup with the 270 ohm resistor, or do I need another value? I don't want to do any harm or have a different issue to chase.

Thanks for your patience if you read this far. At least you were warned that it was long ;-)

[Michael N]

The bucking and misfiring at speed might be the contacts in the TPS, if they're worn might need to move them to a better path and adjust it. Helped on mine with similar problem. Good luck.

Jeff

I agree with checking the contacts at the TPS. I had this gremlin for a while and was checking things in the engine compartment with the engine running. I bumped the wires leading to the TPS and the idle improved. I unplugged the cable wiped the contacts and have been good for years. Good luck.

[Bartlett 914]

I suspect you may have some bad gas.

[ThinAir]

The bucking and misfiring at speed might be the contacts in the TPS, if they're worn might need to move them to a better path and adjust it. Helped on mine with similar problem. Good luck.

Jeff

I agree with checking the contacts at the TPS. I had this gremlin for a while and was checking things in the engine compartment with the engine running. I bumped the wires leading to the TPS and the idle improved. I unplugged the cable wiped the contacts and have been good for years. Good luck.

When writing that novel-length post last night, I forgot to mention that the TPS board was replaced last year with a unit from one of the board members. The connection to the TPS is one of the things I've checked, but I haven't tested with the wire pulled off. Also, I'm running the same Pertronix that I've run for ages.

This morning's behavior was somewhat surprising. Air temperature is mid-50s. When I start the car it idles at about 900 (not higher like it should since the AAR should be open) and it drives smoothly. About 10 minutes into my 20 minute commute it starts hunting when I stop for a red light and I feel a couple of slight bucks when driving, but nothing like what I had previously experienced. Even the hunting behavior seemed to go away within a couple of minutes. If it had run like this all along I probably wouldn't even have been looking for a problem.

[TheCabinetmaker]

Unplug the tps. If it runs better, contact davesprinkle, the maker of the new boards. I have now seen three of the replacement boards not function properly. One just last week. I have one I'm going to send to him to trouble shoot.

[StratPlayer]

I got a new board from dave and it doesn't function properly.

[jsayre914]

Unplug the tps. If it runs better, contact davesprinkle, the maker of the new boards. I have now seen three of the replacement boards not function properly. One just last week. I have one I'm going to send to him to trouble shoot.

Sent my New Board back to Dave last week, he discoverd there was some corrosion on the back of the contacts that was making it impossible to setup WOT. He repaired it and mailed it back to me.

GOOD VENDOR ! (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif)

The bucking is no fun at all

[jsayre914]

p.s.

I am dealing with the similar issues, my car does not run well at all on cold startup. It take about 2 min to get perfect. Then its perfect idle and smoother running.

I am running the wrong (only available) CHT and using the 270ohm resistor in line. I have been tweeking the motor on a daily basis. If I figure it out, I will let you know.
(IMG:style_emoticons/default/beerchug.gif)

[timothy_nd28]

Go ahead and replace your plugs with some freshy's. Then I would find a way to make your engine run a smidge leaner.

[timothy_nd28]

I also had slight misses at idle. I replaced the mechanical points with a pointless module called "hotspark". Then I bought a new ignition rotor, dremiled the resistive material out, and soldered a copper wire in its place. Then I purchased new OEM bosch plugs and beru plug wires. After doing all this, my idle is very smooth. This seemed to work for me, and it's been 800 miles since I have done this work. This may be over kill, but I have a better peace of mind driving my car on road trips.

[DRPHIL914]

I suspect you may have some bad gas.

Bad Gas is a possiblilty - but could be a number of things
re-check your grounds,
when did you last re-place your fuel filter? - how is fuel pressure?

for the CHT, i put a 0-1k ohm Pot. in line and was able to dial it in and then test the resistance, and get an inline resistor for that same resistance.
see if that makes it run smooth

one other idea. no one has mentioned - if you can source a know working ECU, swap them out. I have heard of people having similar symptoms and going crazy checking everything and it turned out to be the ECU!

Keep us posted, -

[shoguneagle]

Ernie,

Thought I would drop into your thread and see how the car is doing/running. I am just across town if you need any help. Know very little about the -fours or D-jetronics/L-Jetronics but ????

[76-914]

(IMG:style_emoticons/default/confused24.gif) any news?

[ThinAir]

Well the news is that I keep eliminating things so I've got to be getting closer to the answer (IMG:style_emoticons/default/smile.gif)

The 012 CHT arrived on Saturday. I tested the R values at different temperatures to match up with Brad Anders' tests. It tested pretty close to 017 with the 270 ohm resistor added. 39F - 10.2K, 61F - 2.02K, 210F - 280 ohms. It seems to run pretty much like the 017 as well (no checking with instruments, just the feel of how it drives). I'm running the 012 without an added resistor, so that eliminates the CHT.

I found that my 043 MPS (that has the best vacuum holding time) doesn't like the 012 CHT - idles smooth for a bit, then dies. I switched back to my original 037 and it seemed to run better than my spare 037 at idle, but all I think I can say for sure is that the problem persists no matter what MPS I run so I don't think it's the MPS.

The TPS has been disconnected and it made no impact on the behavior.

Tonight the battery was removed and all the cables and posts cleaned, including the post on the body. I also double checked every electrical connection that I could find anywhere on the engine (except the injector wiring for the injector points - left this alone on purpose to see if the rest of it affected the behavior.) Still no change in the behavior.

So I figure I'm down to 2 things, distributor/Pertronix/injector triggers or ECU. There is also the possibility of a fuel filter. I run 2 filters, but since one of them is under the fuel tank where I really can't get to it, I'm not going there yet. There's also a sticking injector, but checking injector flow/spray is more work than I want to do yet (and they've been working fine for so long that I doubt they are involved in this).

Since I have a spare distributor all ready to go, I'm going to try swapping that tomorrow night. That will give me a different Pertronix, injector triggers, and vacuum canister in one shot. It will also give me a chance to examine the injector trigger wiring more closely. I know one of the connector tabs is broken off, but I've also been unable to get the boot down into proper position on the connector. I'm hoping that I'll have a better angle on that as part of putting in the different distributor.

Anybody got a spare 037 (021E) ECU they want to loan? How about a '74 ECU? Since I have an 043 MPS and the 012 CHT, one of the '74 ECUs would give me Brad Anders' preferred setup for a '73 2.0L.

The thing that bugs me most about this is that the problem is intermittent. It will seem like things are going well, only to have the bucking & low idle come right back sometime during the next test drive.