Hot Starts

VW based Porsche. In a league of its own.

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914 Rookie
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Hot Starts

Post by 914 Rookie » Thu Sep 19, 2002 9:11 am

I'm new to my '75 2.0L 914. It runs fine until I shut it down, then when trying to start it back up (5-10mins) it won't start. It still cranks. Then I'll wait another 15 mins and no problem. Am I getting a vapor lock ? I didn't think fuel injected cars had this problem ?. Thanks for any help on this.

Ryan72
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Hot Starts

Post by Ryan72 » Thu Sep 19, 2002 10:51 am

This is a common problem on 914's with D-Jet fuel injection, im not positive how the problem is resolved as I had a low tolerance of the fuel injection and converted it to carbs. Im sure someone will chime in any minute to answer your question Image

914 Rookie
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Hot Starts

Post by 914 Rookie » Fri Sep 20, 2002 10:51 am

Thanks. Has anyone used the Bosch "Hot Start Relay" part # WR1 ?

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Dave_Darling
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Hot Starts

Post by Dave_Darling » Fri Sep 20, 2002 11:02 am

That is a relay that should only affect the starter itself. It would be a possible fix if your starter did not crank when it got hot--but it won't do anything for a car that is not getting spark or fuel.

Are you getting spark and fuel when it doesn't want to start? How's the fuel pressure read when it won't start? What kind of shape is the ignition in??

--DD

------------------
1974 VW-Porsche 914 2.0 (Type IV powered!)

Pelican Parts' 914 Tech Geek http://www.pelicanparts.com

914Racer
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Hot Starts

Post by 914Racer » Fri Sep 20, 2002 5:10 pm

It's been hot in CA the past couple weeks. It could be vapor lock even though you have a later model and the pump is up front (I think). The heat from the engine plus the high ambient temps cause the fuel to vaporize in the lines that are in the hot engine bay starving the car of fuel.

-Greg

Eric914
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Hot Starts

Post by Eric914 » Mon Sep 23, 2002 2:03 pm

My car, '75 2.0L with stock injection, will do this occasionally also. I haven't tracked it down yet. It kind of acts like it is flooded and won't start, so I just push the peddle to the floor and crank away. It starts after about 5-10 seconds, probably more like 5....I just counted it off and even 5 seconds seems like an eternity...

JmuRiz
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Hot Starts

Post by JmuRiz » Mon Sep 23, 2002 2:27 pm

I hear ya, happened to me for the first time this summer. I even have a new fuel pump up front. It was VERY hot outside and I only drove for a few miles to a taco bell, ate inside and came out. I was so mad, but after about 5-10 secs of trying it worked like a charm all the way home. Guess vapor lock can still happen if it's hot.

Nathan

914 Rookie
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Hot Starts

Post by 914 Rookie » Tue Sep 24, 2002 12:30 pm

Thanks for the help. I think it could just be a case of vapor lock due to the high temps we've been having lately. I'll worry about the car after they put out this brush in the foothills behind my house !. Greg.

ray greenwood
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Hot Starts

Post by ray greenwood » Wed Sep 25, 2002 12:21 pm

The hot start problem is caused by one of two things...or both. Vaporlock is not really possible, unless the fuel pressure regulator is malfunctioning. This is common. When you turn the car off, the stock D-jet regulator initially drops from about 28 psi...to 16-18 psi. It should stay that way for at least 15-20 minutes before sdropping to about 8 psi. They get rust pits on the plate that is under the spring, capping the line. This could also be getting lost dueto leaking backpressure valve in the pump, or leaking injectors. All will cause either hot starting problems due to vapor lock, or because of, over-richness in thecase of leaking injectors. You can fix a regulator that functions adequately while running, but leaks down a little too quick, by back stopping it with another regulator...even a weak one, whose pressure has been set at about 18-20. So you install it in the return line end behind the existing reg. It works great. The other problem is the CHT. It tends to bank heat, and leave you at the rich end of the setting. Putting about 100 ohms of ballast in line will tell you if this is happening and help it some. It seemed to have more cooling issues with the cht. If you do a quick romp to the store and get the heads heated up, what can sometimes help is to sit and run for a minute or two at idle to get cooling air flow over the cht, to get it to cool down a bit. If you have the intake air temp sensor still pkugged in on your car, that banks heat as well. Between the CHT and The intake sensor, you will almost always have a hot start due to overrichness. This is exacerbated, if the baseline of your MPS is a little rich, or if the outer stop is set a little too far out. The first vacume movements will overenrich as well. It would help to find out if when it finally does start after a hot start episode, if it was a rich start or a lean start. Contray to popular belief, the throttle valve switch has absolutely nothing to do with hot starting, unless you have been pumping the pedal. Ray

914 Rookie
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Post by 914 Rookie » Wed Sep 25, 2002 12:30 pm

Thanks,
I'll start checking off the diagnostics one by one until I solve the problem. I does seem to be running pretty rich ( if that meens anything? ).
-Greg

ray greenwood
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Post by ray greenwood » Thu Sep 26, 2002 10:12 am

Yep, thats a big part of it. If your baseline fuel mixture is already rich, and then...you add in the heat from the heads saturating a CHT that is already maxed, thats an extra bump of enrichment right there. Add too that a combination of say...possibly lower than stock compression...or a few small vacume leaks (which add enrichment by messing with the MPS) the ny ou have too rich of a mixture. I mentioned compression, because too low of a compression ratio will not be able to properly ignite the overly rich mixture. If you are using the stock ignition, type 4 engines were notoriously under-ignited. Thats a factor also. If you are timed to stock ignition timing specs, you are a little under timed as well. All of these things can and will combine in a hot start situation, to cause this problem. By theway, if you have not cleaned the FI triggers lately...do it. That does not help either. Ray

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Dave_Darling
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Post by Dave_Darling » Thu Sep 26, 2002 3:19 pm

Ray, I think you've got the CHT thing backwards.

CHT resistance goes down as the heat rises. The ECU leans the mixture as the resistance goes down. Under about 100 ohms, the CHT circuit has just about no effect on mixture.

See Brad Anders' website for details. http://members.rennliat.com/pbanders

--DD

------------------
1974 VW-Porsche 914 2.0 (Type IV powered!)

Pelican Parts' 914 Tech Geek http://www.pelicanparts.com

SC912E
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Hot Starts

Post by SC912E » Fri Sep 27, 2002 12:46 am

For what it's worth, I've found high temps do some strange things to the electronics in the engine compartment. If it's not a fuel problem it could be a sensor or ecu connection. I had a hot start problem which I traced to a conector in the engine compartment. It lost continuity when it got hot. Just A thought.

Steve

ray greenwood
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Hot Starts

Post by ray greenwood » Fri Sep 27, 2002 8:21 am

Actually Dave...You are correct. I always get lost when trying to describe it. But you just hit the problem on the head (at least the CHT part of the problem). Its what is wrong with the CHT. Its why it needs ballast. To say it has no effect under 100 ohms is not 100% correct. It has no change to the fuel mixture under 100 ohms. During driving, in hot weather, the CHT is a large part of the adjustability problems. It goes straight to about 70 ohms,,,and stays there. Even if you hit the highway after driving in traffic...and get good sustained cooling air blast, the CHT...once hot...stays that way. It stays leaner than it needs to be. After getting onto the highway, and the heads cool just a bit from traffic or hard accleration, it should be...ideally...back up around 125-150 ohms. It has so little outside surface area exposed to the air...as compared to what is screwed into the head, that it just stays hot and is very slow to change. This same thing happens when you turn it off. It stays down at the lean end. Add that to the heat saturation of the ambient air temp sensor...which does enrich as heat goes up, and the usual leak down of available starting pressure on the fuel ring...and you get a hot start situation. Thank you for noticing my automotive dyslexia. the effect is still the same. One thing I have thought about trying, is a sub-miniature relay cut-out inline to the CHT. It would be very clean and add no resistance. When you hit the key, that energizes the relay and switches it to a set 200 ohm resistor. In stant ballast...only while the key is engaged. When you let go of the key, it switches back in line to the normal CHT circuit, which may or may not be ballasted.
If you are noticing a lot of richness when you finally get it running after a hot start, I would reccomnend being sure nothing else is leaking...especially vacume at the MPS, or making note of wether you have pumped the pedal or not. The throttle valve switch will give 9-10 bumps of the injectors each time you fully stroke the throttle with the key on. If your base problem is running just a hair too rich at the MPS settings...or fuel pressure ...or both, stroking the throttle needlessly will cause an apparent hot start with a rich exhaust plume. WAIT...I almost forgot. If you are experienceing rich/hotstarts....also check your PCV valve in the breather tower. If it has a crack in the disk in it (most of them do) then this causes this problem all by itself. It cause the MPS to run wide open at start up. If you have D-jet...with tghe breather tower with the built in funnel...and the single 12mm vacume line coming from it...and going to the plenum...you have a PCV valve. You just don't know it. Ray

Va914
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Hot Starts

Post by Va914 » Mon Sep 30, 2002 9:32 am

Would an electric fan on the engine lid with a thermostat/timer, help with removing heat after the car parked?

If the fan ran for 2-3 mins it may help get rid of some heat?

Just an idea.. Image

Kerry

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