Starting woes

[elwood-914]

My 1.7 D-jet, starts fine cold, but at times after my commute home,(about 40 miles) if I stop at the store it will have diffuculty starting. I'll try about 6 times and it acts as it is going to start but no. Then after about the 6th try it fires right up and revs just fine. Does anyone have an idea what to look for. Thanks for the help.

[3D914]

Sounds like the typical hot-start problem - usually fixed with a relay mounted adjacent to the starter. I think there is a Tech article about this.

Could be a flacky Cyl Head Temp sensor though. I've had that problem as well.

[SGB]

Also check that ol' tranny ground strap (sounds like a BDSM game).

[914GT]

Originally posted by elwood-914
it acts as it is going to start but no.

If that means it's cranking then doesn't sound like a starter problem, maybe vapor lock?

[elwood-914]

Yeah Guy,

It cranks over just fine. It acts as it is going to start but doesn't. When it finally does, I have to play with the pedal to "coax" the rpms up and once it gets past 2K, it revs like normal. It only does this sometimes after it is warmed up.

[3D914]

So Guy's correct. If its cranking then its not a relay problem. Vapor lock is still a real possibility, but check that CHT sensor wire. I'd even check the resistance when hot and see if its within spec.

Since temp is an issue, the possibilites really increase, but work the problem and you'll get it eventually.

Enjoy!

[914GT]

On that starter relay deal - I remember my car had a relay jury-rigged next to the starter. What was the need for this? Too much voltage drop through the ignition switch?

[3D914]

Guy,

Yup! You got it!

[914GT]

Not meaning to get off the thread here - but will I still need it with a new IMI hi-torque starter?

[Dave at Pelican Parts]

Not if the wiring in the car is in good shape. Probably don't need it with the stock starter if the wiring and connections are in good shape, either... But some people thinmk you do.

--DD

[pbanders]

If your car is cranking, the warm/hot start problem you describe is not related to the starter or any booster relay circuit. Hot start over/under-enrichment is a problem with many 914 D-Jet cars. The root cause can either be the ECU hot start circuit (poorly designed on the 015 and 037 ECU's), or it can be related to fuel rail pressurization problems.

Try two different things the next time it happens. First, try turning the key on, then off 5 times. This will enable the fuel pump to run for a total of about 8 seconds, which should pressurize the fuel rail and fill it. If that has no effect, try starting the car this way - with the key off, depress the throttle to the floor and hold it. Now turn the key to the cranking position and hold it there until it starts. Sometimes, a leaky injector will deposit a great deal of fuel in the intake, causing the car to be over-rich during starting (or the ECI problem I mentioned will over-enrich a warm motor on starting). Holding the throttle open will provide more air and will compensate for the overly rich mixture. The reason you open the throttle before turning the key is that if the key is on when you open the throttle, you will squirt ten 1 ms pulses of fuel into one injector bank, due to the action of the accelerator circuit of the TPS, making the mixture even richer.

[elwood-914]

O.K. Today I stopped twice on the way home and both times the car would try to start but would just go "blah" as I am goosing the throttle to try to keep it started, but it dies anyway. After about 20 minutes it started. I stopped for gas in town and the same thing. I have a test relay with me and this time I took the screw out of the fuel rail and manually activated the fuel pump relay, no fuel. Again after about 20 minutes of sitting and occationally cranking to no avail. I went and manually pushed the relay and heard it pump up and then stop.... got in fired right up! Is this the vapor lock problem? Thanks for the advice guys I really do appreciate it and I will try anything you suggest. When the car is cold, starts right up and runs like a champ, but I don't want to stop anywhere except home. Anyone go grocery shopping for me?

[3D914]

elwood,

I don't think its vapor lock. That would be evident whether you stopped or not, and the car would buck because its encountering a lack of fuel while driving.

I suspect the problem is in the ignition wiring, relay wiring - which is not used during engine running, just startup. From your testing above its sounds like the heat is affecting the function of a relay or circuit that powers the fuel pump. If you have a book w/schematics, I suggest tracing the circuit from the fuel pump back to ignition - checking voltage, impedence, and grounds.

Enjoy!

[elwood-914]

Third day in a row!!! This time it died on me while driving. I pulled over and manually activated the fuel pump relay and it just keeps pumping, like it is pumping air. This time it started after about 5 minutes and when I got home I double checked the fuel pump relay and it made a completly different noise, so I am sure it was pumping fuel at that time. I will study the wiring diagrams tonight. Any thoughts?? Thanks a bunch.

[Dave at Pelican Parts]

The pump will keep pumping as long as it is getting power. It does not shut off when it senses a certain pressure, the way that some pumps do. The job of maintaining fuel pressure is done by the fuel pressure regulator--the pump just keeps shoving fuel into the fuel lines. This is nice in that excess fuel goes back into the fuel tank and gets cooled off by the trip.

The pump is triggered by the ECU. The ECU will ground a particular wire, which completes the circuit through the fuel pump relay, causing it to send power to the pump. The FI must have power to do this, and the fuel pump relay also gets power directly from the FI power relay also. Both of them are powered by one of the fuses that are on the relay board itself.

One reason the ECU controls the pump is so that the pump will shut off if the engine stalls (e.g., from a crash). A nice safety measure, I think.

The fuel pump should run for about 1.5 seconds when the ignition key goes from "off" to "on". This helps to start building fuel pressure, though it doesn't get the pressure all the way up to the operating pressure of 29 PSI. The pump also runs when the starter is engaged. It also also runs when the ECU detects that the engine is running at 200 RPM or faster.

--DD

[pbanders]

I would suggest going through the entire fuel pump circuit and renewing and/or cleaning all the connectors, especially the plug at the fuel pump.

[elwood-914]

Well I broke down again tonight but I had my Haynes manual with me and some notes from Brads site about checking voltages at the fuel pump relay. I wasn't getting the voltages described so I started to look at the plug connections and when I pulled the connector off of the relay board (5 white wires) one of the wires had pulled away and was probably making partial contact. I plugged it in and it fired right up! After starting, I went back and pulled the wire back off and sure enough the car died. So I hope this is the culprit, and I thank all of you for your patience with me.

[3D914]

Persistence pays off - Elwood

Congrats.

[Dave Bell]

Old wiring and ground connections to the fuel pump... been bitten a few times by that one on more than one 914.

To diagnois lack of fuel problem quickly, I plumbed a small pressure guage off the fuel rail and tie wrapped it up near the engine lid so I could read it easily.



Worth the time it saves you in diagnosing problems....

- Dave

[elwood-914]

That's a great idea Dave! Any problems with the guage concerning vibration? Thanks.