the 964 KID

I've been driving my car reguarally, and last week I noticed that occassionally, especially when the car was already warmed up, I will experience sluggish starts. The starting issue seemed like a weak battery , but it always had enough juice to get me going. The cold starts have been nice and strong. When I noticed the problem I called my mechanic and made an appointment to get my car looked at; so this morning I went to start the car so I could drop it off at the shop, and it was totally dead. I took my back-up battery which probably had a weak charge, but would start the car. I thought I was alright, but after a few minutes at idle, the car stalled from lack of power. I was surpised since i had been driving the car each day, with no major problems, and out of the blue the battery was totally dead (couldnt even hear the starter crank at all). The only other points are that I put a new alternator in 2 months ago, which has been working fine. The alternator light, in the clock cluster, stayed off when the car was running for that short time (unlike 2 months ago when it was clearly time to get a new one). But it does light up when you put the key in and check for all the lights in the dash - so its not a dead bulb. The only other note, is that it rained on the car last night and i wonder if that played a role in how dead the battery got. Lastly, I have 2 batteries, the main one that I use is high quality and was put in the car back in June, my back up was bought in July. I'm gonna charge up my battery and hook up my multi tester and see how things look tomorrow. Anybody have any suggestions as to what the cause might be? Thanks

Ken.

Adrian

Dear Ken,
Could be a number of issues. Do your electrical checks first. Battery voltage with engine off, 12.4V. Battery voltage at idle, 13.8V and battery voltage at 2000 rpm also 13.8V.
The battery light will only come on if your alternator output is 0V and there is no current draw in the field coils.
When the weather cools electrical problems arise. Normally it is a trashed battery but based on your post you had better look at the alternator. Rebuilt alternators are notoriously unreliable. Working fine can only be determined with voltage measurements.
If the electrical system checks out correctly you might want to look at relay R41 the DME/Fuel pump relay or the starter motor/solenoid.
Ciao,
Adrian
964C4

the 964 KID

Thanks Adrian, I'm gonna check it all out this afternoon, so I'll post whatever I find.

the 964 KID

alright, i'm back and things dont look so good. I charged my battery to 12.4V cold, plugged it into the car and started it up. The battery reading immediately went down to 11.46V and as I revved to 2000 rpm the charge went down to 11.30V, at that point I figured the alternator is sending a partial charge, the battery light still fails to come on, eventhough the bulb is working. The alt that I put in a couple months ago was a rebuilt one, so it looks like I'd better send this one back and put a brand new one in this time. As far as the DME relay, I replaced that with the 993 version about a month ago, so I think thats ok. All signs point to the alternator. Is there anything else you think I should check for?

Ken.

Adrian

Nope you have a failed alternator. I suspect what they did was replace either the alternator brushes or regulator brushes but not both. This is common a brutally frustrating for people like me. Another issue is that they get wet and dry and polish up the slip rings instead of replacing them. The new brushes cut straight through the copper that is left and the output drops to nothing. These are not rebuilt alternators these are repaired units to reduce cost and decrease turn around time.
I would advise you check the connections on the back. There should be a red power lead B+ and a blue field wire D+. Make sure they are connected. The blue wire is notorious for breaking off.
Ciao,
Adrian
964C4

the 964 KID

I just got off the phone with the people at Vertex in Florida, where i purchased the rebuilt alt from, the guy i spoke with swears to me that this is the first time a C4 alt they rebuilt has ever failed. He assured me that they rebuild and test them right at their facility there. I cant imagine that no other alt ever failed, even if they are doing good work. I wonder if anybody has some experience dealing with this company's rebuilt parts. I normally get my parts from Pelican or Vertex, but this is the first rebuilt part I've used, since it was nearly a third of the cost of a new one - but now i know why perhaps. At this point I should just upgrade to a brand new one.

the 964 KID

Adrian, when the new alt gets here I'm gonna pull out the old one and see if those wired are connected, but they were nice and firm just a couple months back, so we'll see. Thanks again.

the 964 KID

OK, this is weird.... I wanted to spend the afternoon removing the alternator, and wanted to turn the car around before starting. I went to start the car, thinking it wouldnt turn over, but it turned over with no problem. Even more odd was that the car stayed running smoothly and never stalled after being at idle for more then 10 minutes (the last two times i started it, it stalled right away). So I opened the hood and check the battery, where as earlier the battery at idle was reading around 11.3V, now it was reading 13.2V, which is still lower then it ought to be, but enough for the car to operate in most daytime conditions. I got a little more gutsy, grabbed a fully charged spare battery, and took the car for a drive. At no point was there any issue. In 45 minutes, I got gas, stopped and started the car 2 more times, again with no issues, I also kept reading the battery and it stayed between 13.1- 13.4 Volts. I had intended to pull the alternator out, but now I'm curious and wonder why it would work (better) now. Are there any reasons for this, or is it still a faulty alt? Once again, is there anything that the rain could have contributed to this? I wonder if, as my car dries out from rain the other night, if the charging will return to normal. Any ideas? I only want to pull that alt out if I have to - which may be inevitable.

Ken.

Adrian

Dear Ken,
Wiring issues I think. I would as I have already advised you to check the D+ connection. It may be damaged along its length. You are going to have to get your hands dirty on this one.
Ciao,
Adrian
964C4

the 964 KID

Thanks Adrian, gonna check it out the D+ connection tomorrow afternoon. Is it possible that the wrong tension on the belt could cause this? It looks alright, but I don't have much experience to accurately judge the tension. One more note, I have suspected a grounding problem in the car in the last month - my oil temp light is floating, on occasion, making the car look hotter then it is. Could be a problem with the thermostat itself too. I believe this because all the fans and belts appear to be operating fine. Is there any chance that this wiring problem could cause a grounding problem? The timing of both issues would make sense. Thanks,

Ken.

Adrian

Dear Ken,
Yes ground problems can cause such problems but you have to start with the basics. I could provide a list of things which MAY! cause the problem but this is not helpful. Effective troubleshooting starts with the basics such as electrical power supply and generation. Intermittant faults like yours often are caused by a failure in the connections of the electrical generation. I have seen and helped fix many variations of the same problem. My main aim is to try and help you fix the problem without costing you a fortune in replacing parts.
Rule number one of troubleshooting is to always look at the last thing you repaired especially if that thing could cause the current problem.
Alternator replacement requires removing wires, re-tensioning of belts, reconnecting of wires etc etc. Major disturbances. I have seen D+ caught up more than once and damaged during re-assembly and vibration eventually causing chaffing and a short. The Alternator is not fused either. I am not convinced that the alternator has been given a clean bill of health yet. I would like you to obtain an AC meter and check for AC on the DC output of the battery. A failing diode pack can cause such intermittant faults as well. They tend to fail under heavy electrical loads and heat. When they cool down they seem to fix themselves, for a while.
Ciao,
Adrian
964C4

the 964 KID

Thanks Adrian, I'm gonna check all that out and see what happens, it certainly makes sense that the replacement of the alternator may potentially be at the root, in one way or another, of my problems.

the 964 KID

Hello Adrian (and anybody else checking this out)

Well, after a lot of headache I broke down and took the car into my best local shop. It appeared to be some kinda electrical problem, which I didnt feel experienced enough to track down - I'm also fairly limited as far as equipment goes, I'm ready to take things apart, but dont feel comfortable enough to mess with certain issues. My biggest nightmare is, like a lot of DIYers, messing up, and the result costing me way more!! Anyway, the shop tells me the charging system is totally fine, working perfectly well - rebuilt alt and all. My problem, or atleast part of it, appears to be caused by a failing temp sensor. Looks like I have to replace the whole unit. I have to talk to my mechanic once more, but can you explain how this would effect my sluggish battery starts? I just wonder if there's another issue to address with my car, or if this is the only problem. Also, I just wanna verify something - in my year car there is no 'check engine' light? Lastly, how much should I expect to pay for the work being done to my car (hours + parts)? They're gonna do an oil change, and replace the entire unit that houses the temp sensor. Thanks a lot, I really appreciate all your help,

Ken.

Adrian

Dear Ken,
Failing temp sensors do not flatten batteries. Which temp sensor by the way? By your post I assume the air temp sensor in the airflow sensor assembly. I cannot see this affecting starting anyway. It is a density correction for the fuel air mixture calculations.
Your sluggish starts are related to electrical problems (assuming alternator and battery are perfectly okay;
Alternator wiring and connections which still need to be checked.
Starter motor, solenoid, connections or earthing
Battery earth cable
flywheel reference speed sensor/connection/earthing
Cylinder head temp sensor/connection/earthing
A battery drain which is flatening the battery.
I wish you had access to a mechanic who did things using basic troubleshooting techniques. Deal with the starting issue first.
Ciao,
Adrian
964C4

Wikkid911

[QUOTE]Originally posted by Adrian

When the weather cools electrical problems arise.

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Hi Adrian,

I know this is true as I have had flat batteries for the last few years during winter but never really understood why. Would any perfectly healthy battery fail if it got cold enough?