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Wait to Start and other odd issue


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Howdy...first post but long time lurker. Sadly I am in a pinch and need some smarter minds than I (which don't take much).

 

Not too long ago my WTS (wait to start) light quit working...I was new-ish to the truck at the time and now living in So Cal I thought it was an ambient temp thing and the truck did not need the warmers. After looking into it it seems either the bub is bad OR the ECU, right? 

 

So, I did a gauge check (via holding the odo button and turning key to on) the WTS light came on at the VERY beginning of the test but did NOT illuminate at the end when all the other bulbs were getting checked per the procedure. So that is confusing to me...some part of the test must get a signal from somewhere different than the other part...or something. BUT I did see the light so I know the bulb is at least intermittently operable. 

 

The other ODD thing that happened was a very slow crank...low batts. The truck has brand new series 31s? They are slightly larger that the stock size. It sat for a week (but it has done that many times since I have owned it). So, I go to jump it and as soon as I connect the cables (key is off and sitting on dash) the Fass fuel pump buzzed to life...WTH? It gets it's signal from the ECU, right? I thought maybe there was a constant going to it and it somehow read the fuel pressure and decided to top up the pressure...then I though maybe the pump was what drained the batts via a fuel pressure leaking down and the pump constantly running. I used the Fass harnesses and wiring diagrams to hook it up  and it looks like the only way it gets power is via the ECU and the relay. I put a new relay in just because I had one, but I doubt that is it. I also had a strange thing happening with my radio and amp cycling on and off...so I just pulled the fuse for both of those. The truck would only hold a charge for an hour even after I drove it around a long time. It did these symptoms for several days. So I take it to my buddies shop to get his opinion and guess what...started like a champ even after sitting a week. DAMNIT! So I bring it home and for the last two weeks it has been fine.

 

However, with the lack of WTS light and the intermittent starting issue (at least in my eyes it is intermittent) maybe the ECU is freaking out and doing oddball stuff. Is there a way to really check the ECUs or just suck it up and get a new (reman) one?

 

Any ideas or comments are very appreciated.

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I know that you said your batteries were new, but it may be worth the time to have them tested.  You may have one that will not hold a charge and bringing the other down as well.  I had something similar years ago and it came down to a bad cell in a battery.  Sometimes it would start right up and other times it wouldn't, there didn't seem to be anything consistant.  Inconsistant voltage can make electronics do crazy things and that can be difficult to troubleshoot.

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Thanks...I load tested both of them and they were fine. It has also been a couple of weeks with no symptoms of a slow or no crank. This morning I did the gauge test again...just kinda going through the motions at this point...and when the WTS light comes on during the very first part of the test I can hear the Fass prime itself...then during the later part of the test the WTS light never come on again. I never hear the pump prime when I start the truck normally...at least I don't think I do. I have heard that a WTS that fails to illuminate can be a sign of a bad ECU...can someone confirm?

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I can go 2 3 4 or more weeks before my truck is used. so I have it plugged in to a smart charger maybe 1 amp. If I do not do that it will be dead in a couple of weeks. I have not gone any further in checking the loads on the battery but that seems normal for all the garbage that need to run when just sitting. my toyota that is not used much has a small solar charger from a VW that is used during shipping to the usa. alway up even when I go away for a few weeks.

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It true the lag in WTS light is a sign of a failed ECM. What is happening the ECM is having errors or internal issues getting booted up and the first function does typically is check the IAT sensor for manifold temp and then turn on the grid heaters. So since the memory in side the ECM is damaged there is booting errors so the ECM keeps retrying to boot till it make it. This is the lag I speak of. So now what caused this failure? Typically the alternator with a bad diode creating excessive amount of AC noise.

 

So at this point the only way to start is to wait for the WTS light to come on. Then you know the ECM is booted up.

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I have used those VW chargers for years...I used to work for VW when they first came out those...they are great.

 

So I guess I will look at the alternator and see if I can find any fault there...but diodes are tricky sometimes. I guess I should start looking for an ECU at a good price as well. My truck will start now...as long as the batteries have a charge which they have now for the last couple of weeks. Such a random, odd symptom that slow/no crank is...damn.

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