No start when hot - solenoid?

[Shawzy]

Hi all

Need some quick tips on a hot start problem.

Symptom:
On key turn starter relay clicks, no action on the starter. Only occurs when engine is hot (~180).

Doesn't happen often but want to address what I can now so I don't have to push start again with my shirt and tie on. Nothing like running behind your 911 in a suit.

Issue - after a 45min drive at normal temps, car won't start after engine is shut-off for a 5min period (after a fill-up, after a quick coffee break, etc.) I therefore attribute this issue to heat failure, as the car has no trouble starting after sitting for a while (2+ hrs). Also note this problem is low frequency, it's happened to me 2x - in about 50 drives.

More - after I have had this trouble I can usually start and stop the car numerous times without fail when hot. Just because it failed once doesn't mean it will happen again that same day.

I am thinking starter solonoid at fault as it the problem occurs only when hot.

Ignition switch could be at fault (i.e. worn contact points) but doesn't make sense to me as symptoms always occur with a hot engine.

Any feedback appreciated!

[John Brandt]

Replace your ground strap fiRst and see if that fixes it. A $5 part from napa and 5 min with 13mm wrench is all it takes.

[sfoster13]

Had the same problem, replaced the starter and everything is fine. Have also heard vapor lock could be a cause and you need to change the accumulator and fuel filter.

[Jk369]

I seem to have a propensity for this problem; both my SC and my PU truck do this. The truck was doing this about 5 years ago so I changed the starter and it was pricy, within months same thing. I would rock the truck to get it to engage in a different spot and it starts. I have only had to rock the SC once or twice, mostly letting go of the key and trying again works for both. Call me lazy but the truck keeps on going I can only assume the SC will do the same. Checking the ground is a good idea though.

[Shawzy]

Ground strap on bat end replaced, but not strap from engine to frame. Strap looks ok but perhaps i will pull and clean or replace it.

I think I am looking at a new solenoid and starter rebuild.

Jk369 - I will try the rocking trick, and if i can reach it I'll tap the solenoid with a rod to see if that helps.

Either she's not getting enough juice or solenoid is pooched, just wanted to see if any others had luck with this. I don't think vapor lock the issue, assuming of course engine turns over in this case.

Thanks for feedback, I'll likely start with electrical check and then solenoid replacement (hoping it can be removed and purchased separate from starter!).

[JTL]

I had this exact problem on my car and ended up rebuilding the started a getting a new solenoid.
To diagnose get a helper to tap the solenoid with a hammer while you turn the key. Mine started right up every time, hot or cold with no start initially.

You may want to have the trans in neutral with handbrake & brake on.

jt
-84 targa

[Shawzy]

Thanks JTL, I figure this is it. Were you able to purchase a solenoid independant of starter?

I think my starter is fine, and if it is would want to go with solenoid only.


Thanks

[jester911]

Funny this should come up now. I have had my car almost 6 years and never a start problem. I drove the car on a race track for almost an hour and when I turned off the key it did just as you described.

Ended up pushing off to get it out of pit lane. Parked in the paddock and an hour or so later it started right up.

I have had my car on the track before too and this never happened. I guess I will be looking into my solenoid and starter as well.

[Sigurd]

I had the same problem in my car. I took the starter apart, cleaned it, and put in some new grease. It has worked perfectly all summer.

[RoninLB]

Happens to me sometimes.

I did a direct starter jump from the battery lug on the starter to the solenoid and it spun the engine so I figure the wire is ancient and couldn't deliver the added amps to hot solenoid windings. My ignition elec part is new.

In the mean time I installed a direct solenoid jump momentary on Cole-Hersee button in the engine compartment.

[mjw]

I had the same symptoms, it got to the point where it wouldn't start unless the engine was stone cold. Mine was caused by poor electrical contacts in the ignition switch (easy fix). I don't think that my 33 year old starter switch contacts were capable of delivering adequate current to a heat soaked starter.

[Shawzy]

That's interesting mjw, I didn't think about a hot starter drawing more current than when cold but I guess that makes sense.

I will try and run some voltage drop tests listed in the pelican article on troubleshooting a starter. Either that or I will rig up a bypass.

As far as the old switch goes, I understand that all are prone to fail over time mainly due to a lack of a diode across the solenoid terminals. The back EMF voltage generated when solenoid collapses is quite large apparently; this causes a nice fat spark at the ignition contacts that causes them to fry over time. I have heard of guys putting a diode at the solenoid for this reason to shunt this voltage to ground. Anyone know of this approach? They do this on many solenoid applications in other industries I am told. Not much help for us with old ignitions, but will help those who have replaced them.

[RoninLB]

Originally posted by Shawzy
I have heard of guys putting a diode at the solenoid for this reason to shunt this voltage to ground. Anyone know of this approach?

They do this on many solenoid applications in other industries I am told.

yes.. details are burried in my "stuff". I just changed the sw as part of 100k re-do of some electrics.


the 75amp Bosch relay comes in both configurations.

[JTL]

Yeah. Performance products has solenoids available separately. I don't usually shop there but it was the only obvious place to get one.

Rgds, jt

[RoninLB]

Originally posted by JTL
Yeah. Performance products has solenoids available separately. I don't usually shop there but it was the only obvious place to get one.

This 75amp relay pn has the diodes. I use 2 similar without the diodes for headlight relays. They should outlast a new engine's lifetime. It draws around 350-450ma.



http://www.waytekwire.com/index.htm



Product Detail for Item #: 75252

Category: Relays
Sub Category: Power

Description: BOSCH POWER RELAY
BOSCH# 0 332 002 156
4 TERM, PARALLEL/SERIES DIODES

Selling U/M: EA
Weight: 0.1940
Price: $19.4161

[blur]

The bakelite on my solenoid is cracked, sometimes it starts, sometimes it just clicks in and doesn't turn. Problem is, I can't seem to find a part number for the solenoid. I'm not at home now and can't take off the starter to see any part numbers so could anyone who knows please post the part number for the solenoid of a SR68X Bosch for a 911SC???

TIA

[Carl83911]

This just happened to me today when I went home for lunch. I hooked up the charger and it started right up. The extra juice gets the selonoid going. I now carry a portable charger in case it happens. I should just change my selonoid or maybe clean or replace my ground straps.