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1979 Eldorado - 350 Olds motor - fast idle problems

6408 Views 29 Replies 5 Participants Last post by  CarScope
I have a 79 Eldog with the 350 Olds fuel injection motor. When I start the car, and its in park, the motor runs super, super fast!

I removed the breather and figured I would just turn the idle screw to slow the motor down a tad, then I discovered the idle screw cant be adjusted as it does not have a visible head on the screw.

Is they're anyone out there that can help?

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There was also a clip at the bottom of the plunger. That part is not important and some are discovered to be missing. That means either someone already removed it or it was ingested by the engine...
Thanks for mentioning that silly clip. I'm not an enthusiast, just working on a customer's nice 79 Seville. It looks like the clip was possibly installed wrong and kept the seat's "upside-down top hat" part from going into the seat of the throttle body (assuming it was supposed to). The clip was sticking out and keeping the whole thing sitting on top, above the seat. I could not find a picture that showed the assembly with the clip anywhere. I just took it off and it all worked better. He wants it right so I'll be ordering your improved unit. The plunger has one of the vanes broken. Do you sell the plunger parts/assembly too? (assuming you have time to respond to the forum quickly- if not I'll buy one somewhere.)

I need to make sure his misfire is something small first, and if so- will be ordering soon.

Thanks again... wasted a bunch of time figuring it out. Appreciate your post. Maybe others will find it first.
Wow. Thanks.
The misfire won't likely be a problem diagnosing, unless it gets weird with injector issues, then I might need the manual and diagrams. ;) I will definitely save the manual from the site, if I can find it. I didn't see it at a glance.

Originally, I just couldn't tell it was misfiring with the cold idle so low and stalling. I started with that issue first. It was very likely latched (though I did not see a picture, the very term describes it perfectly).

Fuel pressure was decent: 30-34 running, 40 with the hose off. But it acted like it may have been a pump at first, in the lot trying to drive into the shop... though it was not getting air either, probably just flooded it.

Actually, he came in for a door lock clicking/battery draw issue (repaired the popped-apart switch for that). He did not mention any driveability issues, which is kind of funny as horrible as it was running.

I'll PM Monday after I check the misfire. Thanks again.

btw, Nice diagnostic tree on the site. Unusually useful, especially for that era.
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Oh, I found the manual- on the home page :rolleyes:. I was checking menus.

This guy may do the upgrades EFI, he said he wants it right. Some of them will be a little pricier to have a shop them. (I am his mechanic doing it for him at our repair shop). But he has spent some money making it pretty, it'd be worth the investment, I'd think. It may have 50k original miles, btw! Looks new, original stickers under the hood etc.
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I did see the info about their common failure and was planning on checking them. I only saw one sensor with that style connector though. It is on the front left, as the manual says is the coolant. Where is the intake air sensor meant to be? I suspect someone changed the sensor and connector to a single wire (if they even exist). If so, it may now be grounding through the manifold instead of a second wire... I will measure resistance Monday, and if needed pull it/them out and see which is in the air intake.

Thanks again. And for the chart, that saved some time :)
I saw the gauge sending unit (or one of them) next to the ECT... it had no wire on it, btw. I was going to look into that Monday too. Funny they had two sensors, in a way that would alert people better who don't watch the gauge, or scare them further when the second light comes on. I did not even look at the cluster to see what this has in the way of lights and gauges,

Does the switch/blower delay have the same connector as the sensors? I assume it has two wires?

And I looked around back there for the IAT, but apparently missed it. Thanks. I'll look closer.

I am dumbfounded by the care and attention you guys take... you must love these old caddies. Thanks a lot Scott. If the customer doesn't run out of money I'll get this one running like new, or better (with your upgrade).
Very good then, I saw two single wire senders and the ECT up front on the intake. That leaves the IAT in the back and another single wire I probably am forgetting about or did not see. That makes it easier. Shouldn't be too hard to see which single wire sender/switch is doing what, now that I know what to look for. Thanks again.
Looks like 4 cylinders are misfiring (1,5 and 4 and 6)! I'd have never guessed that many. No gross vacuum leaks apparent. slowed with added fuel, like they were dead misses. Good spark at cap dfor all four and least at cylinders on 1 and 5. No fuel on the plugs, good compression

I checked the fuel injectors on the left bank so far. 1 and 5 have no injector pulse. This system appears to have a positive supplied pulse rather than the negative grounding modern method. I have to leave the shop for now, but will ohm check all the injectors when I get back, to see if one or more are shorted. It looks (by color wire) that it is left and right bank fired, and I have misfires on both sides. I suspect one or more bad injectors, one on each bank.

btw, the temp sensors were matching 944 ohms before starting and seem fine, or at least close enough.
They are swapped, and no pulse even with them all unplugged. Looking for ECM pinout now. I assume the same ECU power source drives both banks, so it is either ECM internal or pin or wiring to that bank.

I'm looking for those answers in diagrams now.
You can barely distinguish the wire colors, but they are swapped.
I have not found the ECM connector view/pinout yet.
You can barely distinguish the wire colors, but they are swapped.
I have not found the ECM connector view/pinout yet.
I found the diagram on the site you shared with me. As far as I can tell, it's not two separate power supplies to the ECM, so I shall check the pins at the computer.

Thanks. Alldata definitely did not have the diagram (though their library might have, if I asked.)
I do know that the 8 injectors fire in groups of 4 with this system. I know Bruce Roe posted the injector groups before but I couldn't find it quickly. I did find the following which I think we can use/ translate because we know the firing order 1-8-4-3-6-5-7-2. He wrote "The Cad 79 system used 2 banks of 4 port injectors each, alternately fired on alternate crank revolutions by special HEI reed switches."

So I guess that means if we use "up"/ "down" then if 1 &2 are up 3 &4 are down 5 & 6 up 7 & 8 down. I may not be thinking this throw thoroughly but it seems like that would mean 1, 2, 5, & 6 would fire together and 3, 4, 7 & 8 would be the other group. If that's true could your "4" above be "2" or are those 2 connectors swapped?

Where do you recommend getting an ECM for this bird? I took it apart and saw nothing to solder, and no power is coming out of injector group one. All injectors ohm ok on both banks, at least with the engine cold. And there are no shorts to ground in the harness. Are these injectors known for shorting when hot but testing ok cold? If so I may suggest replacing them. The EGR passages are plugged, if he wants it perfect, I could take the manifold off and clean the passages and do the injectors at the same time.
Thanks for the diagrams, the colors and pin letters were correct but the connector was on the end not in the middle as one picture said.
Thanks for the diagrams, the colors and pin letters were correct but the connector was on the end not in the middle as one picture said.
I talked to him and am making the estimate for the customer. Thanks for all of your help. I'll post some pics here of the car for you and Mr. Roe.
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