Car starts and then stops

1450 Views 12 Replies 6 Participants Last post by ghnl, Jul 22, 2015

Comben

Discussion Starter · Jul 19, 2015

I need you guys ! My ´89 Spider starts and runs for maybe 5-10 seconds and then stops. If I try to start it again it cranks but do not start. If I leave the car for some time it will start again for 5-10 seconds and then do the same thing again. I have changed both fuel pumps since it looked like a fuel starvation problem but no cigar... The plugs do not smell gas and they have heavy black deposits that I've never seen before. Last year I have changed the fuel pump relay and all the fuses are good. Any ideas ??? It happened to me on my last ride last year when the car just stopped about 500 feet from my house.

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ghnl

· #2 · Jul 19, 2015

My first guess is a faulty drive relay or fault in the signal to the drive relay.

The drive relay is supposed to get a tachymetric signal from the coil to know the engine is running. It then powers on the fuel pumps. There is a bypass circuit to power on the pumps during cranking. My guess is the fuel pumps are powered on by the bypass circuit but not the drive relay.

There are other things to check - like the two flywheel sensors. More info is in the L-jet diagnosis page - see the link in my signature.

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rogerspeed

· #3 · Jul 19, 2015

check the coil and its connections

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Comben

Discussion Starter · #4 · Jul 19, 2015

Thank you for the information. The drive relay or the fuel pump relay as they call it in my book was changed last summer :imp

hard to find and expensive ). There is also a connection to the main relay but i don't know where that one is located. Any idea ?

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ghnl

· #5 · Jul 19, 2015

The drive relay & main relay are both located next to the FI computer - under the parcel shelf behind the seats.

Do you know what brand relay was used? The Bosch relay is the more expensive one. There is another brand (KAE?) that fits but there have been reports it does not always function correctly. The most commonly reported difference is that the KAE relay will power on the fuel pumps even if the engine is not running (not the proper operation). But I've read that it sometimes just doesn't power on the pumps.

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Comben

Discussion Starter · #6 · Jul 22, 2015

Do you know a method for testing those relays ? I tried to find the answer in your article : L-Jetronic... But could'nt find one. Excellent article BTW... Except that a lot of the pictures don't show up and I tried both my Mac and a PC. About 80% of the pictures don't show up and it goes for my IPad too !!

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ghnl

· #7 · Jul 22, 2015

Comben said:
Except that a lot of the pictures don't show up...

Oh dear. I will contact Greg and see if we can fix that. Some of the photos were on an old web page - our prior internet provider was bought out so I assume that old web page is gone.

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sloboy89

· #8 · Jul 22, 2015

ghnl said:
Oh dear. I will contact Greg and see if we can fix that. Some of the photos were on an old web page - our prior internet provider was bought out so I assume that old web page is gone.

I have the entire article in .pdf form with all of the pics if that would be helpful. Is there a way to post a .pdf here?

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Norseman50

· #9 · Jul 22, 2015

You can "attach" a .pdf file by using the "Manage Attachments" utility while creating your post. Just choose the .pdf file you want to attach like it's a .jpg photograph you want to embed in your post.

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sloboy89

· #10 · Jul 22, 2015

Norseman50 said:
You can "attach" a .pdf file by using the "Manage Attachments" utility while creating your post. Just choose the .pdf file you want to attach like it's a .jpg photograph you want to embed in your post.

Thanks, Norsemen. Attached is the L-Jet Diagnostics article by Greg Gordon and Eric Russell.

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Shiraz1965

· #11 · Jul 22, 2015

My car had the same symptoms when I first purchased it a few years ago. Turns out the PO wasn't aware of the inline fuel filter out back and had never replaced it. Replaced both fuel filters and problem went away like magic!

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Comben

Discussion Starter · #12 · Jul 22, 2015

Fantastic, now I can see all the pictures. Now for those relays. Is there a way to test them ( Main & drive relays ) ??

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ghnl

· #13 · Jul 22, 2015 (Edited)

The drive relay is the odd one. It needs a tachymetric (pulsing) signal from the coil to 'know' the engine is running - it then sends power to the fuel pumps (there are two, they are both powered on together). I don't know how you'd check for a tachymetric signal or replicate that. (My knowledge of electical things ends at 'keep the smoke inside the wires'.)

But you could easily test for voltage at the fuel pump. A test light (12V bulb) might be even better than a voltmeter. The fuel pumps should get 12V when the key is turned to 'start' because there is a bypass circuit to ensure the pumps are powered on during cranking. And they should get 12V when the engine is running if the drive relay is working properly. If you do not get 12V under either condition then check the wiring to the fuel pumps. If you only get 12V during cranking then check connections at the coil and to the drive relay. If no faults found inthe connections/wires then the drive relay is suspect. The only test I know is substitution with a known-good drive relay.

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