Odd diesel Rabbit starting problems

[DieselAlltheWay]

84 Rabbit turbo diesel got a replacement 1.9L engine from a 94 Golf to replace the 1.9 that was there previously (till it suffered a timing malfunction). Swap went well and we put the battery in the hatch in order to make room for an intercooler. When it starts it seems to run just fine, took it around the block and it even idles OK, after much headache getting it to start. Timing properly set with precise timing tools.

Problem is, it refuses to start for the most part. It seems to crank initially but then stops and won't crank after that. It just makes those clicking noises as though the battery is fully drained (which it isn't but that's what sounds like). If you let off the key and crank it again, it will repeat the process but won't start, even with another car boosting it. We tried to boost it straight at the starter (thus bypassing the long battery cables that now resides in the hatch) and still no change. We even replaced the starter in hopes it would solve the problem, didn't (started appeared OK to begin with). Doesn't seem to be the ignition switch as it has the spring and returns fine, with the proper pressure so it looks like that too can be ruled out. All connections have been checked and double checked several times.

We're at a loss.

[82vdub]

What is your voltage at the starter terminals when the engine is not cranking, and what is it when your cranking the engine?

What wire size cables did you run between the battery and starter/chassis main wire feed? You have to size conductors for voltage drop for a given amp load and distance that the load needs to be carried.

Have you tried using a remote starter switch to actuate the starter solenoid? This bypasses all factory wiring as you'll cross between the main power feed to the starter to actuate the solenoid. If this works every time, then you have a wiring issue. If it doesn't, you may have a wiring issue or a solenoid issue. Whatever you do, make sure the car is in neutral before you use a remote starter device.

The solenoid may "drop out" when there's less than 8 or 9 volts. Depending on what you have when you're trying to start the car, the solenoid may not have the voltage to stay pulled in.

[Fatmobile]

Any warm/hot spots in the cable connectors means a bad connection.

[DieselAlltheWay]

Yes, tried all of the above suggestions. Used a 4 gauge welding wire for both the positive and then later the neg, as the neg being connected to the back of the body was dropping voltage. So after adding a new wire to the front of the engine from the batt's negative post, it has been rectified. Even while connecting the batt straight to the starter via short cables the problem is still there. Yes, we tried two diff starters, both of which work fine and so the solenoid is not the problem.

The great mystery here is that everything is in place, all system seem to be functioning properly and yet the car won't crank as it should. I dread having to have the car towed to a shop for repairs as often the bill at over $100/h will kill you. Having a new baby arriving in 3 months is not a good time to be throwing money into a car (when we already have 3 others running), despite the fact the wife absolutely loves that fast bunny.

[82vdub]

Take the numbers off the cables you used and google data for that specific cable and find out the resistance per foot. You'll need to calculate voltage drop. Your #4 cable may be too small.

Depending on the KW rating of your starter, it may pull a lot more amps than you think. I've seen 1.0-1.7KW starters listed for VW engines. A 1.0KW starter pulls 83A (amps) and a 1.7KW starter pulls 142A.

Depending on what resistance the cable you're using has carrying 100+ amps to the front of the car, you may have such low voltage at the front that it won't pull the starter solenoid in. Measure the voltage at the starter when it's cranking and when it's not.

[Fatmobile]

Where are you connecting the ground cable?
The stock trany mount location is weak.
I connect to the starter's top mounting bolt.

[bscutt]

if you are running cables from the back of the car I'd suggest #0 or no smaller than #2 gauge. That's a lot of run to drop voltage over

[DanHoug]

have you replaced the $2 starter bushing? that can make an enormous difference in cranking speed. since your starters (2) aren't turning at times, replace that bushing if you haven't done so.

-dan

[DieselAlltheWay]

here's a minor update:
Finally had the chance to visit the garage where the Rabbit sits at for the first time since starting this thread. After reading all the replies here I have decided the best thing to do is to try and put the battery back in the front using stock wiring, as it seems the consensus here is that the long welding wire to be the problem. Well, I had very limited time and didn't have the chance to do it but hope to do it in the next few days. I don't want to remove the intercooler (sitting where the batt goes) but hope to just try and fit the batt back in place for a test. This would be the best way to eliminate the long wire as a possible reason for the starting problems.
Oh and the numbers on the wire say 4 gauge, 800V welding wire. They're roughly 13 to 14' long.

And wasn't able to do a reading on the voltage as I was alone and this is best done with two people (am I right?) where one is cranking while the other is reading the voltmeter. This is something I hope to do when I return there and my friend is there.

Starter bushing? Maybe, but seeing how we tried two diff starters and they both were working I'm afraid it may not be that simple a fix. Hope so though, so will keep that in mind should replacing the batt not work.

Again, thanks for all the help. i will post updates here once I get some bunny time under the hood.

[Una]

4 gauge is way too thin for that long of a run. 4 gauge is about right inside the engine bay on it's normal 2 foot run.

[82vdub]

4 guage is rated for about 80amps. A 1.2KW starter pulls 100A at 12V. Parallel run #4's for both the positivie and negative and that may solve your problem. However, having someone help you take voltage measurements may be easier to figure out where you have to go next.

[DieselAlltheWay]

82 Dub, it currently has long 4 gauge wires for both pos and neg. We had started with only the long cord for the pos (as my friend has in his mk1 GTI and works fine). Initially we had the neg bolted to the hatch but that showed a huge drop in voltage. Using a digital voltmeter showed that, so I went out and got another 14' of the 4 gauge wire and connected it to the engine bay in hopes it wouldn't drop so much. Doing this seemed to have helped as it did start fine the first couple of times and then the same problem came back. Guess doing a voltage reading is a smart thing to do before attempting much else. Will try to get this done tonight if my friend can be there.

[82vdub]

You can measure the voltage across the battery terminals, and then at the starter on the big positive cable running to the starter and the chassis ground (or starter body itself). You may find only a little different in voltage between these two readings at these locations. It's when you put a 100A load on the conductor that you will see the most effect. I agree that you should run the negative ground back up to the source of the largest load, the starter. You should also run a smaller ground to the chassis back at the battery location too.

On old Chevy's I've owned, a lot of people would have a starter problem. What would be the solution to a lot of the problems is to connect the ground strap from the back of the motor to the firewall, or make the connection better. Otherwise, the current was not flowing through a low resistance connection between the engine block and the chassis, causing the starter issue. Most people that don't understand electricity who move batteries or install huge amps in their car don't realize that they have to use properly sized cable for the load expected, distance run, and the resistance of the cabling, connections, switches etc installed in the system. All cabling is not the same either. The reason why I asked you to look up the information on the cabling used is because all #4 cables do not have the same resistance rating to them. There are cables that have less resistance than others, so using one cable over another does have effects on the system.

[DieselAlltheWay]

Votage: it now drops to 10.3 when cranking, which is up from the 7.8 before running the neg to the front.
This still too low? Anyway to improve on that, possibly by going with a thicker cable, and if so do I need to run thicker cable for both the neg and pos? Adding this intercooler is costing way more than I had thought and depending on additional costs I may just dump the idea and put the batt back out front. Not even sure if an intercooler would add that much to an already quick car.

[bscutt]

Ru a second 4 gauge wire in parallel with the existing positive wire (also on ground if you aren't grounding through the body too) and that should reduce the voltage drop a good bit. Again knowing the resistance per foot of the wire you have would allow a calculation of voltage drop (assuming we know starter current draw - assume 100 amps?) but I would bet on doubling up the cables.