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rough idle of 79 Eldo

Started by john rutenberg, November 14, 2005, 10:26:35 AM

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john rutenberg

I am just getting my Eldo and was told before I bought it that it was starting to idle rough. I was told it drove fine but wasnt smooth at idle anymore. I was told it wasnt like this in April but has stated running rough in the past few months. Do these computers go bad on these cars and is that usually what seams to solve most of the idle issues ( aside from usual maintaince)? Years ago before I knew anything about the 78-79 Seville, I had one. It only had 30 miles and I bought it from a dealer. I was talked into replacing changing the intake manifold gasket and lifters at a tune of 500 dollars. This solved nothing. The idle still was rough. After I gave the car away. I was told that idle issues on those cars were related to the computer. I was told that if I had spent the 100 dollars and replaced the module that this would have solved my problem. Is this so??? Does anyone have a 78-79 Seville or a 79 Eldo with the 350 Fuel Injected engine that knows about the idle issues?

Tod - North TX CLC

A rough idle can be a number of things, so it is a matter of troubleshooting.

Does the car idle rough in neutral, with RPMs around 900? Or does the idle get rough once the car is in gear?  If the rough idle is only under load, then you might have a firing problem (bad plug/wire/dist. cap/rotor - the standard stuff) or a defective fuel injector.  Check first to see that all of the cylinders are firing.

Next, is the idle rough at all times?  Or does it only appear after the car warms up?  If the idle is smooth when cold, then gets rough after warm-up, you need to check to make sure the RPMs are still up after warm up.  The fast idle valve may be shutting the air flow down a little too far.  You can adjust the idle speed on the air intake (large adjusting screw on the front).

Anything else that has some bearing on the rough idle (air conditioning off or on).

If that is not the issue, then MOST of the idle problems can be related to vacuum - you will need to check all lines, and the unit that they attach to to make sure that there are no leaks.

Make sure that both fuel pumps are running, that the chassis fuel filter has been recently changed, and that you are maintaining approx. 40 psi. at the fuel regulator.

The EFI cars should idle smoother than carb engine, in my opinion, and with few exceptions should provide reliable service.  I will tell you that I have 4 cars with this engine, and I have never had a rough idle situation that was cured by replacing the ECU (computer).  My experience has pretty much been all or nothing when the ECU was at fault.

I strongly advise you to purchase the service manual, and make sure it includes the EFI section - this will be invaluable to keeping your car servicable.

I have purchased an Olds intake, quadrajet, and most of the other items I need to make the conversion to carb, but so far, I have not been inclined to make the backwards leap!  



Andrew 10642

Two things. . .

You need to understand that the Bosch fuel injection system in the car.  Its not really sophisticated, and is blamed for a lot when actually its another more simple problem at fault.  Its beyond the scope of this forum, just do a D-jet search in google, youll find a good summary.

You need to make sure the basic tuning of the car (spark) and vacuum settings are all correct.  Otherwise, this car will be impossible to get running correctly.  The EFI parts are not cheap.  Learned about this system on a 73 Volvo, its no wonder they went to DFI in 1980!

john rutenberg

Guys thank you so much for your advice. I will recieve the car on Monday next and when I do the first thing I am going to do is check everything out. I have 80-81-82 Lincolns with EFI and I know those cars like the back of my hand. I know the emmissions systems as if I designed them. Im just going into new territory with this car. Im going to change the plugs first and check to see how the cap and rotor are as well as the wires. Then Im going to check all the vacuum lines for leaks and then the timing. Ill check all the emissions system items and if it has an 02 sensor Im going to replace it no matter what (if it has one, that is). Ill check the diverter valves and go from there. Is there something in particular like a senor in the manifold that I need to be aware of? Ill also put an additive to clean the fuel system and replace the fuel filter (where ever it may be) and Ill make sure all is right before I start going further. I am buying manuals as we speak so Im totally informed about this car. Thanks again!!!!!!! If you have any more advice please dont bother to help me as I will need it!

john rutenberg

Question? Which AC plug should I use? Rapid Fire, Platinum or regular? Also, there seems to be some odd thing in the book, it said I needed a R47SX but the Delco sight said R46SZ what do I use?

Mike #19861

Originally the correct plug was the R46SZ, but Delco has discontinued and changed up some numbers since, so whatever the current Delco catalogue says would be correct.

 The standard Delco plugs will work well in your car. No need to upgrade, however, I have had good results with Rapidfire plugs.

  Mike

john rutenberg

I havent recieved my manuals yet does someone happen to have a diagram of the lay out of the EFI system for the 79 Eldo?

Tim Pawl CLC#4383

There actually was a service part in the form of a 1000 ohm resistor that plugged into the wiring harness (included all the molded weatherpack connectors) on one of the temp sensors that fixed the rough idle by basically telling the computer that it was colder than actual and to enrich fuel mixture.  I will try and locate this info for exact part number.  I had it installed on my 1979 Eldo several years back and it fixed a rough idle, ofcourse yours may be a different issue but it worked on mine.

Lars Kneller 8246

My experience has found that the most common problem for rough idle on these EFI engines are a bad EGR/EPT.  They are not available new that I am aware of, but are available used.

john rutenberg

Well, my 79 Eldo has still not left the shop since I bought it. We have done just about everthing known to man. On the scope it runs so clean it will pass smog with flying colors. Still the rough idle issue is present. I finally asked them to do a fuel pressure test and sure enough only 32 pounds of pressure with the vacuum disconnected from the throttle body. I told them to replace the manual fuel pump as it should have as much as 60 pounds with the regulator dissconnected. I figure what the heck replace them both for 30.00 each just do both for safe measure. Also, they have found that when they disconnect the vacuum advance and put a pump on the fuel pressure regulator and pump it to 39 pounds the car runs just like a purring kitten. Why would I get a vacuum advance of 43 when connected????? The timing is set at 10 and the idle is set at 600. When you connect the vacuum advance up it runs the timing up to 43 degrees and the rpms raise up pretty high as well. They are gonna change the vacuum advance ($10.00) they think the retention spring is bad. Man what is the deal. Do all these things go wrong with a car that sits too long??

denise 20352

> Why would I get a vacuum advance of 43 when connected????? The timing is set at 10 and the idle is set at 600. When you connect the vacuum advance up it runs the timing up to 43 degrees and the rpms raise up pretty high as well. They are gonna change the vacuum advance ($10.00)

    Not being an expert on this engine, I can tell you that 43 degrees is just about right for idle when full manifold vacuum advance is applied (on most engines).  It is also perfectly normal for idle to increase when going from 10 to 43 degrees of advance.  What youre saying, to me, sounds like the vacuum advance unit is working properly.

-densie

john rutenberg

Thank you very much. We replaced the pumps and was able to get another 5 pounds of pressure out of the system. It runs almost perfectly except for a very slight miss. We changed the vacuum advance and it was the exact same, so you must be right about the advance. Finally he took some brake clean and went around and found that the throttle body is leaking air at the base. They are going to remove the TB and check for any defects on the manifold and the TB ,I think the gasket is bad. I think this will take care of all my troubles. I can say when Im finished I can drive this car from LA to NY and back several times without worry.

Dwayne Knoff

How much change do you have invested in this daug?  My 78 Seville cost me an arm, a leg, and then some before conversion to 4 barrel rochester.

Dwayne