[Duanewong]

I need this part for the 1976 Cadillac Seville I am working on.
The second one I tried didn't work at all for starting and running under its own power. The first one I tried worked partially to run under its own power. I think the original computer didn't work very well. All three computers I have experience with seem to act slightly differently for starting the car.

I am trying a fourth one in December 1, 2020 from Summit Racing, but it is backordered from AC Delco.

The newly flashed and remanufactured Analog Computer is supposed to work on 1976 to 1979 Cadillac Sevilles, without having to be reprogrammed to the car's specific year.

Reflowed circuit boards are supposed to last a long time.

The link I have is actually a Cardone part offered on eBay, which I also was having trouble finding online.

I tried Blue Streak twice which is remanufacured in Mexico by an American firm. But, they did not work perfectly.

AC Delco Professional is supposed to be the best.

Duane Wong

 

[Duanewong]

For Cadillac Seville 1978 Cardone Engine Control Module ECM ECU | eBay

Find many great new & used options and get the best deals for For Cadillac Seville 1978 Cardone Engine Control Module ECM ECU at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[Duanewong]

I removed the Fast idle 'heater' from the throttle body and checked it. That was okay.

In fact, when I do get it started the fast idle is about 1200 rpm, and over 5 or more minutes, depending on outside temperature and throttle body temperature, the fast idle slows to normal speed of 650 rpm,

So, the fast idle bypass which is controlled by the fast idle heater is okay, in my opinion.

The engine starts fine when warm from operation.

The engine does not start immediately when not run for a few hours to overnight not run.

I believe the problem is related to the computer, particularly the circuit that enriches the fuel by increasing the length of time the injectors open when the starter solenoid is engaged, when you crank the engine, which happens when cold like 45-60 degrees F.

Note. I tried three different ECU computers, and so far each acts differently when starting cold.

Once started, after several cranking attempts,it runs fine at all speeds, and also starts up fine, with the first ECU I got from Blue Streak, at least.

Duane Wong

 

[Duanewong]

It's probably your idle air control, those were a common failure point. I think it may have had a different name back then. It just twists out of the throttle body and is probably hard to find now.

I priced a used fast idle bypass heater on eBay. It was $235 to $305 or so, which is almost the price of an ECU computer.

 

[Duanewong]

I priced a used fast idle bypass heater on eBay. It was $235 to $305 or so, which is almost the price of an ECU computer.

I know what you are saying about the idle air control. I changed the IACV on my Northstar engine in a 1997 cadillac deville limousine, twice.

The 'fast idle heater' just extends a pintle that closes throttle body air bypass that makes the engine run faster when started cold, combined with wider pulse width of the fuel injectors when the engine coolant temperature sensor is showing cold coolant.

It is like open loop on later engines that use an oxygen sensor.

Duane Wong

It's probably your idle air control, those were a common failure point. I think it may have had a different name back then. It just twists out of the throttle body and is probably hard to find now.

Fast Idle Heater does twist out, and I used throttle body cleaner spray on metal throttle plates.

It appeared clean before and after.

It had no effect on cold hard starting problem.

 

[Duanewong]

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.
View attachment 593399 View attachment 593400

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.
View attachment 593399 View attachment 593400

That's neat you have parts for repairing common problems found on the 1976 Cadillac Seville.

The way it acts, though, is almost like it is fuel starved when initially cranking the engine for several seconds.

Then, if you just tap the starter switch it starts up immediately.

And, when the engine is run a couple of minutes to an hour or longer, the car restarts normally.

I tested the ohms of the coolant temperature sensor, which is the same part # as the intake air temperature sensor, but they were both within specs.

The car was at a dealership and they tested the temperature sensors and what you call the FIV Fast Idle Valve, which were found to be functioning normally.

Thanks for your thoughts on the problems, though.

 

[Duanewong]

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

'76 to '79 Cadillac Seville home page

1976 1977 1978 1979 Cadillac Seville information

www.cadillacseville.org

 

[Duanewong]

'76 to '79 Cadillac Seville home page

1976 1977 1978 1979 Cadillac Seville information

www.cadillacseville.org

I've been through the flowcharts for EFI on the 1976 Seville.

 

[Duanewong]

I've been through the flowcharts for EFI on the 1976 Seville.

 

[Duanewong]

I don't have a gauge, but when it was at the dealer they said it had 38-40 psi.

Fuel filter changed last summer when it was in the shop.

The ECU doesn't have a removable EPROM, and is analog not digital.

The exhaust seems to be sealed.

The engine has eight multiport fuel injectors.

'76 to '79 Cadillac Seville home page

1976 1977 1978 1979 Cadillac Seville information

www.cadillacseville.org

 

[Duanewong]

I don't have a gauge, but when it was at the dealer they said it had 38-40 psi.

Fuel filter changed last summer when it was in the shop.

The ECU doesn't have a removable EPROM, and is analog not digital.

The exhaust seems to be sealed.

The engine has eight multiport fuel injectors.

'76 to '79 Cadillac Seville home page

1976 1977 1978 1979 Cadillac Seville information

www.cadillacseville.org

The external fuel pump was changed last summer but not the in tank fuel pump. I don't know why they didn't change both.

 

[Duanewong]

I think the fuel pressures were lower on the first generation fuel injection specifications in the 1976 Cadillac Seville compared to my 1990 Cadillac Deville where it was 10-15 psi, or so, higher.

I'd have to look at the invoice to be sure of the exact pressure noted.

68° F to 75° F last summer.

Ignition on, starter off.

I am not sure I'd the technician looked at the pressures while cranking it, or while it was running.

I think he had only one figure written down.

Vacuum controlled fuel pressure regulator was changed, too, last summer.

The thing that gets me is every ECU I have tried has different behaviors for starting the engine. Some worse some better.

One ecu flooded the engine after turning it off.

Another, would not start the car at all.

And, the one in it now, has hard cold starting, but if you try long enough it starts and runs flawlessly after that especially when warm.

Duane Wong

 

[Duanewong]

Looking at the website you point to it shows what looks like max fuel rail pressure is
you could do the test they stated :

7. Since diagnosis this far has failed to find a reason why the fuel pressure is low, begin to suspect that the pump or the regulator may be the problem.
With the engine at idle, pinch off the fuel return hose. This action is how the regulator raises the rail pressure.
If the pressure does not increase to at least 46PSIG, a defective chassis pump is indicated.

Also I see this has a MAP sensor, check for a hose leak/vacuum or test to see if MAP is faulty when cold
No way of knowing with those ECMs if they in fact were setup for your engine, model or year

Get tests out of the way if it is a fuel, MAP or intake leak, using the diag flow of that website you use

MAP voltage values should pin down if there is some vacuum leak (inverse of MAP) or again use a smoker

I checked the MAP hose to the ECU which has the MAP sensor in it. No leak down found with my vacuum pump.

I even totally disconnected the MAP hose to see what it would do while running.

Black smoke came out if the tailpipe. Lol.

I think Bendix originally had a lot of different ECU numbers for 1976-1979 Sevilles. But, the recently remanufactured ECUs are supposed to work with a wider range of options. I am not familiar with why this is the case.

 

[Duanewong]

I checked the MAP hose to the ECU which has the MAP sensor in it. No leak down found with my vacuum pump.

I even totally disconnected the MAP hose to see what it would do while running.

Black smoke came out if the tailpipe. Lol.

I think Bendix originally had a lot of different ECU numbers for 1976-1979 Sevilles. But, the recently remanufactured ECUs are supposed to work with a wider range of options. I am not familiar with why this is the case.

Also, I checked the number of clicks heard when slowly squeezing the vacuum cruise control bag and noting how many clicks the injectors make when the ignition is on, but no RPMs, which is a way to check the adjustment of the Throttle Position Sensor.

 

[Duanewong]

What you need to find out is what MAP is reporting and follow the diag process has for MAP testing on that website
to determine what MAP reports on cold idle and if fuel system is functioning correctly

I am thinking that it is possible the fuel pressure was normal after warming up, but maybe when it hasn't run for a while the pressure is low.
I haven't had it checked under those conditions.

I read the in tank pump has a filter. And, since the in tank pump hasn't been pulled out, I assume the old filter may be clogged.

I think that is the next thing to go after.

When the car was at the dealer last summer they drained and filled the tank which they said smelled like turpentine.

The technician wrote on the receipt, I have to drive it more.

 

[Duanewong]

38-40 PSI fuel rail pressure seems low and at what temp or RPM is that ?

Is there a fuel regulator, and is it vacuum controlled, if so check that hose of leak ?
Is regulator adjustable, and if so what happens if railing fuel rail PSI to more like 45 PSI ?

When starting cold and idle is high about 1,200 RPMs something is driving ECM as to timing or
what it command to the fuel injector pulse width ON times

Check vacuum, what is reading when cold started
Do leakdown of fuel pressure, with 8 injectors must have a fuel rail and it should have a valve to
screw on a fuel pressure tester to assure it is not what the issue is and also assure the regulator is
working correctly or adjusted for proper PSI

If there is some type of intake leak which will effect vacuum then ECM may be fooled as to what engine mode the ECM is

If fuel system and injectors not a issue then how about getting or making a smoke machine and looking for small leaks

The fuel pressure regulator is not adjustable, but was replaced with a new one last summer.

 

[Duanewong]

The fuel pressure regulator is not adjustable, but was replaced with a new one last summer.

I am thinking if the pressure is 1/2 or like 20 psi or lower while cranking the starter, maybe that points to a fuel pump problem. In this case the next pump to replace is the in tank pump.

However, I haven't gotten feedback from any technician who has worked on it that this was actually occurring this way.

 

[Duanewong]

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

Scott, thanks for your deep thoughts on this matter. I think you and ZR-1 have a good understanding of the problem I have on this vehicle and good possible solutions.

I will follow up with what I find, when it gets a little warmer outside in the Spring of 2021 if I learn anymore about the subject.

Duane Wong

 

[Duanewong]

Scott,

That would be useful. I already sent the original ecu in as a core, though.

The one that works halfway is installed but was remanufactured by Blue Streak and I purchased that online from Rockauto, but they are out of them now, after I tried a second one, with no plan on getting more.

 

[Duanewong]

I found this photo posted

of the ECU opened up to view the circuit board from a 1977 Cadillac Seville.