[1979 Eldorado]

Hello, It's almost certain you have a bad coolant temp sensor. They are very easy to check. There are actually two sensors which feed information through their resistance to the ECU. At 60-70F they should both read roughly between 950 and 1000 Ohms. If it's cold out and especially the coolant temp sensor fails with open circuit, the most common, you will not be able to start he vehicle. I had the same issue and nothing was available so I did a lot of research and I've been making professional replacements with the original factory 2 pin connectors for a little over 2 years now. I just joined this site but I am a frequent contributor on the Cadillac site I found prior to finding this site. Check yours before you buy anything; easy with an Ohm meter. The replacement PN is 1609968.

If the ECU is bad there is a member on *************** who rebuilds them. I would 1000% recommend sending yours to him if you still have an issue which you think is ECU related but there are some simple things you can check first. If the issue is cold start though the diagnostic points you to check coolant sensor first (total of 3 coolant sensors on you car so you need to check the 2 wire sensor) and then second check the air temp sensor located normally behind the throttle body on the intake (same resistance I mentioned above).

As for the FIV Fast Idle Valve it controls bypass during cold start and results in fast idle followed by closing after warming. That PN varies but after 2 years of working on them I have finally created a plug-and-play replacement for those as well. The PN are as follows: GM PN 1628898, GM PN 1617956, GM PN 606776and is also known as Bendix PN 1181290 and Bendix PN 1181835 My replacement is the cream/ natural colored one found on eBay but I sell both the sensors and FIV's to forum members at a discount on that other forum.

Best regards,
Scott
PS: Someone is already using the forum name I use on *************** but I am "79 Eldorado" there and "Punched455" on eBay.

 

[1979 Eldorado]

You may want to check the resistance again but check it at the ECU plug (the wires from the sensors run to the ECU). It would be less common but it really sounds like a coolant temp sensor issue. If you checked resistance at the sensor though maybe the ECU isn't getting the proper reading.

If I recall correctly the fuel pumps run for the first few seconds with key-on but they do not run during cranking. Obviously they run in the run position once the car is started.

Cadillac published a checklist chart of most common causes for almost any EFI related issue. I don't recall which manual I saw the chart in though. If I can find that chart it would be interesting to see what order they list other items and what other items they list. If I come across it I will post it.

Scott

 

[1979 Eldorado]

I recently spoke to Bruce Roe who has repaired/tested more of the original ECU's then most of us have seen cars which need them. He mentioned he had one recently which was an aftermarket replacement or was reworked without the original components. I know you are saying that they should work with more combinations than did the originals but if you still have the original I would send it to Bruce. He can repair/replace most of the original components and he can put the ECU through a lot of different evaluations tests. He's also very reasonable.

Back to the fuel pressure and pumps. I know the in tank pump was discussed but don't forget that there is a small piece of special submersible soft hose in the tank as well. If that starts to crack even if the pump is working there will be some pressure loss. The 38-40psig sounded to me like the proper pressure. I thought it was 40psig for these.

A couple of other details as I know: There are 8 injectors but I believe sets of 4 take turns firing. Second: Bruce told me once when we were discussing cold start that the pumps run for a few seconds with the key on. They then stop running while you are cranking. So my start procedure is turn the key to the on position for a few seconds without cranking and listen for a sound change. Once I hear the sound change I crank. After I changed both sensors the car starts in about 3 seconds.

There is still a chance, even with good sensors, the proper value isn't making it to the ECU. That's if there was an issue somewhere in the harness. Since you've changed the ECU a number of times I think I would try measuring the sensor resistance but at the plugs which normally plug into the ECU ( as opposed to just checking near the sensor). The table in the Service Manual is also light on precise values and there is obviously some range and you mentioned they measured within range. If you tell me the intake temp and what the sensor reads I can tell you how close that is to what I would say is typical of what I normally see.

Scott

 

[1979 Eldorado]

Hi Duane,
I totally understand the "gets a little warmer outside" comment I'm waiting for that event myself for some car work.

I don't know if we can send attachments in a PM or I think they call them DM's here but I have Bruce's entire list of ECU PNs. I spoke to him and he told me I can send it to you. Having it you can at least see what the various ECU's you have likely came from. He could check it out for you if it gets warm enough to remove it; no need to drive the car. He can repair almost anything in the originals but there are some aftermarket overseas sourced replacements which he cannot fix. I have the impression at least one of the ones you referred to may fall in that category. The best would be to send him the original from your car or if not one with original contents.

He did mention that the 76 and 77 Seville ECU was essentially the same except the control means for the EGR but it was something almost nobody would notice. It had something to do with both temp and vacuum as opposed to only vacuum if I recall correctly. Even other ECU's may work but the mounting brackets might be different. I've made some of the rare "large car" brackets for Bruce and he can change brackets. Anyway I will send you the list if I can figure out how to attach it.

Scott

 

[1979 Eldorado]

Duane,
Glad to hear the news! Bruce is great and always fair.

Scott

 

[1979 Eldorado]

Somewhere I have a nice article that an owner from Australia wrote about his experience and the help Bruce provided. The same owner has a couple of my first sensors.

Scott