running on 3

3mta3 · Post by **3mta3** » Tue Oct 11, 2005 4:48 pm

My car is 71 square, all stock w/FI. Starts ok w/ good idle and sounds good. Problem is it is running very weak and when I pull plug wire on#4 no change in idle, all others do. I have verified spark, I think, by holding wire to ground but plug itself looks unused, brand-new compared to others. I have done fuel by pulling injectors, saw squirt appears equal. Timing, valves, points, wires, plugs all done. I bought this car cheap and was hoping to be able to make it reliable daily driver, it is gonna start snowing here real soon and need my car for work, can't get stranded. Any help very appreciated. Thanks, Rob

Speedy Jim · Post by **Speedy Jim** » Tue Oct 11, 2005 5:27 pm

Have you done the crucial test: compression test?

If there is compression (like over 80), I would look for
possible vacuum leak peculiar to that cyl.

Speedy Jim
http://www.nls.net/mp/volks/

3mta3 · Post by **3mta3** » Wed Oct 12, 2005 11:10 am

Negative, haven't yet...will do it today. I have already checked for leaks, sprayed wd40 around intake boots and throttle base plate. The spray looked like it was being sucked in but did not change idle.Saw a post that may help me concerning dizzy trigger points "@ base of dizzy". I think I will check these, too. Do you have to remove dizzy to get these, do you know? Thanks, Rob

Post by **Marc** » Wed Oct 12, 2005 11:38 am

It depends upon how the distributor is oriented, the points are in a little "drawer" that slides out of the housing. You'll probably need to pull it, but do the compression test before you bother.
D-Jetronic only has two injection events for the four cylinders - fuel squirts as the intake is opening for one, and at the same time the injector on the next cylinder also squirts. So, if it's a trigger point problem it'll affect two cylinders, not just one. A problem with just one is usually a bad injector or wiring to it, but you've ruled that out already. A vacuum leak could cause a high idle, or low vacuum that would make all the cylinders run rich, but isn't likely to kill one cylinder like it may on a carbureted engine.
If it's not a bad plug/plugwire/distributor cap, it must be low compression.

3mta3 · Post by **3mta3** » Wed Oct 12, 2005 1:48 pm

The results are in! Comp. as follows #1-110 #2-95 #3-105 #4-95. I did squirt a little oil and all changes minimal, a couple pounds maybe. I am gonna double check valves tommorow. The other 3 plugs appear to be sorta black, maybe a little oily but pretty dry, #4 looks brand new. The car doesn't blow any smoke except for maybe a little white on startup if it has been sitting a couple days. I know comp. #'s are a little low but are they so off that this could cause my problems? Thanks, Rob

Post by **Marc** » Wed Oct 12, 2005 2:13 pm

Compression readings vary from gauge to gauge and with cranking speed so one can't say absolutely, but assuming typical accuracy they're ALL too low. Odd, though, that it'll idle on #2 even with the same reading as #4, and the new #4 plug implies that you aren't the first one trying to figure this out. What happens if you pull the plug wires one at a time at a higher speed (1500+ RPM)? A cylinder with compression just a little low for idling will typically be contributing some by then....

ridinthedune · Post by **ridinthedune** » Wed Oct 12, 2005 2:33 pm

you said you checked spark by holding wire to ground. I would check it with the plug attatched to the wire and grounded, then you know if you are getting spark "to the cylinder".

3mta3 · Post by **3mta3** » Wed Oct 12, 2005 5:53 pm

OK I will check the spark like that, thanks. What I mean about the plug looking new is that I changed the plugs maybe 500 miles ago and w/ exception of #4 all others look the same, kinda black but not really oily, I don't think, as they are pretty dry. With compression numbers that low am I looking @ complete rebuild, or could I maybe get away w/ "new" heads as I have a set in what appear to be good, almost new condition. Thanks, Rob

ridinthedune · Post by **ridinthedune** » Wed Oct 12, 2005 7:07 pm

Did the problem start about 500 miles ago?

3mta3 · Post by **3mta3** » Fri Oct 14, 2005 7:08 pm

No it was the same, has been that way since I bought it, but we lived in FL then and didn't really notice it on the flats like I do in the mountains

3mta3 · Post by **3mta3** » Sat Oct 15, 2005 10:37 pm

There has got to be someone that can help me. I triple checked the valves today...small dif but all good. To me it sounds like timing, like I ai8m @ the small mark just to R of TDC, then set valves. Also noticed hose from charcoal can to L side (3/4) does not go to elbow on that side, surely that cannot be prob?

3mta3 · Post by **3mta3** » Sat Oct 15, 2005 10:48 pm

Also did 1500 RPM's test and no dif, it still sparked but no change in engine. Would throttle valve switch have anything to do do w/ this? I asked on other line about this but didn't get answer. Thanks Rob

mightymanx · Post by **mightymanx** » Sat Oct 15, 2005 10:52 pm

Did you check your valve clearance or did you check to see if they are working?

to check if they are working have some one turn the engine by HAND and with the valve cover off watch them open and shut to see if that is happening.

3mta3 · Post by **3mta3** » Sat Oct 15, 2005 11:00 pm

Yes, I have done that. The valves appear to be going in/out the same as others.

Max Welton · Post by **Max Welton** » Sun Oct 16, 2005 9:53 am

3mta3 wrote:No it was the same, has been that way since I bought it, but we lived in FL then and didn't really notice it on the flats like I do in the mountains

In the mountains? Altitude will most definitely affect compression test results. Higher altitude means less air and lower readings. Your readings may actually be OK. Where are you?

Max