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1980 FBC
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I played with all the wires around the sensors and controls on the engine.

Started the car adding some fuel in the TBI, car started but ran rough still.

I started going through the fuse block with the engine running, reseating the fuses, and one of the two injector fuse I could remove completely without any difference in the engine operation. Found a blown injector fuse... OH that could be it. Replaced it, car ran much better, and then it burnt again after running ok for a couple of minutes.

Played with the injector wires, and the passenger side wire loom, did not notice any short, but replaced the fuse, and now the car runs better but still rough a bit.

HOWEVER, now with both injectors injecting, I get 8psi fuel pressure.

to do:

1) find a short on the passenger side engine wire loom feeding the injectors; same area that had a short for the coolant temp sensor wires.
2) understand why I get low fuel pressure; is it a regulator issue, or is it a fuel pump issue, etc.
The most likely spot for an injector wiring short is the rubber fitting where the wires poke thru the throttlebody.

Ham fisted people put the air cleaner on without the busing in place and cut the wires.
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #363
The most likely spot for an injector wiring short is the rubber fitting where the wires poke thru the throttlebody.

Ham fisted people put the air cleaner on without the busing in place and cut the wires.

Ham fisted! :) I vote for that. I'll inspect these in the area :)
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #365
Confirmed that both injectors show 1.5 ohm. So the fuse blowout was likely a wiring issue. Unless one injector has an intermittent short.
 

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1980 FBC
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Confirmed that both injectors show 1.5 ohm. So the fuse blowout was likely a wiring issue. Unless one injector has an intermittent short.
Does the shop manual give a specification for injector resistance?

I don't remember if the injector voltage is dropped below 12 volts somewhere. If not 1.5 ohms would land up with 8 amperes current draw which would not work well with a 3 amp fuse which is what I remember being in there.

Even 5 volts puts the current draw over 3 amperes.

?
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #368
Interesting comments regarding the current draw... Yes, 1.5 ohms was measured with wires disconnected. The impedance is measured with DC current via the ohm meter; but actual current used by the ECM to drive the injectors has a non-100% duty cycle, so impedance will be higher and current draw will be lower. Did not find the actual expected impedance in the troubleshooting manual...
 

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1980 FBC
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Interesting comments regarding the current draw... Yes, 1.5 ohms was measured with wires disconnected. The impedance is measured with DC current via the ohm meter; but actual current used by the ECM to drive the injectors has a non-100% duty cycle, so impedance will be higher and current draw will be lower. Did not find the actual expected impedance in the troubleshooting manual...
Yes, the duty cycle is always less than 100% but peak current draw still exceeds 3 amperes.

The only way to take advantage of the duty cycle wold be to spread the current draw out over time with a large capacitor. Dunno if they actually do that.

To your point, it's also possible they have a resistance in series with the injectors on purpose.

Maybe someone can look up the specified resistance in TFM.
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #370
Because both injectors have the same impedance, while only one fuse was blowing, I'll deem the injectors OK.

But I did notice that there was only 8psi of fuel at idle.

In the troubleshooting manual, they say to block the fuel return line and see if there's more than 9psi. In my case, it did not change anything in the fuel pressure, stayed at 8psi. It means, it's likely not a fuel regulator issue. But that fuel pump is only 2 years old...

I let the engine run for a few more minutes, and then it suddenly died.

Turns out, the fuel pump stopped sending fuel altogether. It sounds like it's spinning, but no fuel at all, even at the fuel filter level.

Wow. Guess I need to drop the fuel tank.
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #371
After dropping the gas tank, I realized there was a bad electrical connection to the fuel pump. Fixed that. After that, can started and ran, albeit still with a shitty idle. Then, a couple of weeks later, the car wouldn't start at all, and now with zero fuel pressure.

Time to close the shop for the year. Put some WD40 & oil in some strategic locations, and then cover.

Next year, next year, until next year.

20181027_100928.jpg
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #372
Different area of the car, to keep me busy during the winter...

I had fixed the automatic level suspension sensor 'arm' (attached to the differential), and I had made it adjustable. Was a combination of metal, original parts and JB Weld.

However, the plastic on that thing is dead, and disintegrated.

After some investigation, found these parts to fix that in a better way. Those end connectors are DIN 71805, and the size of the ending is 8mm.

Will be much better, sturdier and still adjustable.

20181108_143759.jpg
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #373
573261


I'm depressed with my Cadillac. it won't run well. Seems like it's running very rich. I am not sure what to check, where to (re-)start, What's depressing is that the car was running OK last year, and now, there's this mysterious relapse.

Thinking about selling the car, because I tried long-term storage and that did not work (I was aiming for that elusive time in the future when I will magically have "more time" to spend on the car). But would NOT sell it to an imb***le looking to perform an LS swap and install 28-inch wheels...
 

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1984 Eldorado Biarritz
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I agree. Common break point is at the hose that connects it to the throttle body as it has to undergo a bend. Nevermind storage and critters.
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #376
I agree. Common break point is at the hose that connects it to the throttle body as it has to undergo a bend. Nevermind storage and critters.
Thanks for the hints; turns out the MAP hose is ok. But I went deeper, checked the codes and then, in the engine data, the throttle position reads 15 degrees while the throttle is not depressed at all. This reading is out of a 0-31 degree range, so it actually means, the DFI sees the throttle opened at 50% when the car is idling, flooding the engine with much too much fuel. I double checked on the TPS check point and I get 2.57 volts. TPS is shut? I replaced that not that long ago...
 

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1984 Eldorado Biarritz
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Makes sense, and considering the TPS ranges from 0-5 volts, 2.57 means half throttle. Not enough room to adjust the TPS that far out, so I would lean on kludged TPS. But I'm pretty sure it can read to higher than 31 degrees, IIRC its something like 70-80, properly adjusted of course. Did you ever set the TPS according to the manual with the ISC retracted?
 

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1981 Cadillac Fleetwood 4-door V-8-6-4
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Discussion Starter #378
. Did you ever set the TPS according to the manual with the ISC retracted?
Yes. I got a new TPS, installed it and now, the car runs fine... I would have never suspected this! That sensor was new!

I looked inside the bad sensor -- not much to see; the resistor is printed on a piece of plastic, there's a spring, that's about it...

573791


573792

573793
 

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1981 Biarritz, V864
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19 Posts
Hi Gilles, I came across your thread last year from a V864 search on this site and have learned lots already from all the work you have detailed here. Thanks very much for posting everything in so much detail!

Was wondering how work on your car is going this year as I have been watching regularly for any updates, but nothing in past 9 months, so I thought that my question that follows below might be a way to give a gentle poke to encourage you for more.

Your last posting about the throttle position sensor has me wondering about an issue I have with my V864, that maybe you have run across already. Mine is in an 81 Biarritz that has about 140K kms on it. It still runs very well in V864 mode around town, but out on the highway I have an issue where it doesn't want to leave 4 cylinder mode when cruising at something like 100 kph and starting to go uphill. I have tried pressing down on the gas pedal quickly, slowly and even pressing on and off at different rates but she just won't drop back to either 6 or 8 cylinder mode until I floor it and the transmission drops to second gear. When it does drop to second gear it is a VERY harsh shift and then the system seems to work properly again to go from 8 to 6 and then 4 when she goes back into third. I have a switch under the dash to bypass the third gear signal to the ECM and if I use that instead it is a nice easy transition back to 8 cylinders with no harshness at all. Any experience or thoughts on this?

If you would rather not side track your thread with this please feel free to send me a PM.

Thanks and I hope that you are doing well in these challenging times. Dave
 

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96 FWB
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Be patient. He hasn't been on for 7 months. Mayhaps just search '864 not working' on here and DuckDuckGo. Toggle Relevance to 'Date' for better hits.
 
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