1991 Loyale idle/acceleration issue

[GeneralDisorder]

Have you checked for a vacuum leak? The most common cause of an incorrect idle on a MAF car is a vacuum leak - air gets in through an alternate path, doesn't register on the MAF, and thus fuel is not calculated for the actual amount of air - causing a lean condition that is unable to sustain idle. 

Also could be the idle air control valve isn't working properly but if it idles at 2k with the MAF unplugged I would say that's less likely at least.

2k idle there is enough airflow that a small vacuum leak would not contribute a significant percentage and would not make a big difference in MAF voltage. 

These SPFI systems are fairly reliable - make sure you have addressed the obvious stuff like cap/rotor/plugs/wires, ignition timing, vacuum leaks, etc. You can chase tail for a long time if that stuff isn't working properly. 

If you had the equipment to actually read live data from the ECU you could look at MAF grams per second, but as that's not likely to happen you will have to resort to "reading tea leaves" on this one. You could graph the MAF sensor voltages at various RPM and see if there's a large non-linearity at the low end of the range. They should respond fairly linearly from 0.5v to about 4.5v. The scaling in the ECU for grams-per-second vs. voltage is unknown though so it would be hard to determine if the voltage at idle is actually around the proper range. But most engines are around 1 to 1.2v at idle...... not a hard rule but typical. 

GD

Edited August 18, 2021 by GeneralDisorder

[Ionstorm66]

3 hours ago, Phil Hyde said:

UPDATE:  After removing the TPS, I was able to confirm that it reads "closed" (A-B continuity) in the throttle closed position.  A-B stop contacting at some small angle of rotation, which I assume needs to be adjusted to correspond to the feeler gauge specifications.

I re-installed the sensor and rotated so that A-B have continuity when the throttle is in the closed position.

Starting the engine produces the same result as before.  Idles up somewhere around 2K then dies.  Feathering the throttle will keep it running.

At this point I feel pretty confident that the engine should at least idle.  CTS reading checks out for cold start.  TPS is reading closed which should be good for idle.

Am I missing something?

How long does it idle at 2K? It should fast idle until the coolant temp gauge starts moving. Even on a 100F day mine still fast idles on a cold start for a minute or so.

Does it hunt for the idle before it dies? AKA rpms surge.

 

Also my personal three "killer" items to check on any EA82s: 

Make sure the engine grounds are clean. Ground comes from the battery to the starter body. Then from the engine to the harness via a ground point on the intake manifold. Remove both of them and clean the terminal and block where it mates. The one from the battery to the body is usually ok, and not as important for the engine to run. Every EA car I've ever worked on has had terrible grounds. On my personal cars I install a extra ground from the alternator to the battery directly.

Check all of the Fusible links. They are fragile, you can replace them with fuses if you have issues.These love to cause the same issues as a bad ground, especially while driving as the vibration moves them around.

Last check that the screw is installed and right on the rotor in the distributor. Though the fact it idles without the MAF kind of rules that out, still good to check. I've fixed 2 DOA cars but just reinstalling the screw.

 

 

Also check that the belt accessories spin smoothly. I had a car that wouldn't idle, turned out the power steering pump had a bad bearing. It didn't make a ton of noise, but the drag killed the car at idle. EA82 doesn't make much power at idle lol.

Edited August 18, 2021 by Ionstorm66

[DaveT]

The CTS testing ok only at cold temp doesn't mean it is good. 

[Phil Hyde]

7 minutes ago, DaveT said:

The CTS testing ok only at cold temp doesn't mean it is good. 

I see your point, but does it mean it would cause a car not to idle cold?  I'm just trying to establish a baseline.

[Phil Hyde]

21 hours ago, GeneralDisorder said:

Have you checked for a vacuum leak? The most common cause of an incorrect idle on a MAF car is a vacuum leak - air gets in through an alternate path, doesn't register on the MAF, and thus fuel is not calculated for the actual amount of air - causing a lean condition that is unable to sustain idle. 

It is next on my list.  Given the combination of behaviors, I was going for big fish / low hanging fruit first.  

Thanks for the suggestions.

[Phil Hyde]

20 hours ago, Ionstorm66 said:

How long does it idle at 2K? It should fast idle until the coolant temp gauge starts moving. Even on a 100F day mine still fast idles on a cold start for a minute or so.

Does it hunt for the idle before it dies? AKA rpms surge.

It starts, goes up to around 2K, then dies - all in a matter of seconds.  No hunting.  you have to feather the throttle to keep it running.

I will check the grounds - thanks for that.

[Ionstorm66]

21 minutes ago, Phil Hyde said:

It starts, goes up to around 2K, then dies - all in a matter of seconds.  No hunting.  you have to feather the throttle to keep it running.

I will check the grounds - thanks for that.

That sounds like fuel pressure. The pump primes up, but then cant keep the pressure up when its running. Will it start back up if you shut the key off and try again?

 

The car will run with almost any vacuum leak, just poorly. I've had the brake booster unplugged and it still started.

[Phil Hyde]

3 minutes ago, Ionstorm66 said:

That sounds like fuel pressure. The pump primes up, but then cant keep the pressure up when its running. Will it start back up if you shut the key off and try again?

 

The car will run with almost any vacuum leak, just poorly. I've had the brake booster unplugged and it still started.

Yes, it restarts every time.

[DaveT]

2 hours ago, Phil Hyde said:

I see your point, but does it mean it would cause a car not to idle cold?  I'm just trying to establish a baseline.

I haven't had enough different CTS failures to have a solid answer for that. 

I did have another problem once that seems similar - the car wouldn't idle.  Had to hold the throttle to keep it idling.  It was also intermittent.  Turned out to be the wire in the engine harness that goes to the Idle Air Control Valve.  If that coil doesn't get drive, or it's dead, no [or not enough] idle air.

[Dee2]

On 8/13/2021 at 10:48 AM, Phil Hyde said:

UPDATE: I unplugged the MAF sensor and the car started right up.  Maintains a ~2K idle and does not die.

 

23 hours ago, Phil Hyde said:

A Starting the engine produces the same result as before.  Idles up somewhere around 2K then dies.  Feathering the throttle will keep it running. ..... Am I missing something?

Earlier you said that unplugging the MAF kept the engine running .  Have you replaced the MAF ?

[Phil Hyde]

11 minutes ago, Dee2 said:

 

Earlier you said that unplugging the MAF kept the engine running .  Have you replaced the MAF ?

I have one on order.

The funny thing about the unplugged MAF behavior is that you'd think running in this manner would rule out a fuel pressure issue.

Edited August 19, 2021 by Phil Hyde

[Dee2]

52 minutes ago, Phil Hyde said:

I have one on order.

The funny thing about the unplugged MAF behavior is that you'd think running in this manner would rule out a fuel pressure issue.

It does. 

Unplug the MAF.  The computer will default to preset air/fuel settings.  The engine should run normally.    This should allow for verifying that the fuel pressure is not a problem.

This is only a temporary solution as the computer won't make any adjustments for varying conditions.  So eventually, you will need a working MAF.

[Ionstorm66]

2 hours ago, DaveT said:

I haven't had enough different CTS failures to have a solid answer for that. 

I did have another problem once that seems similar - the car wouldn't idle.  Had to hold the throttle to keep it idling.  It was also intermittent.  Turned out to be the wire in the engine harness that goes to the Idle Air Control Valve.  If that coil doesn't get drive, or it's dead, no [or not enough] idle air.

If it was the IAC it would never rev up to 2K on the start unless the throttle stop was way out. Plus it would keep running if it was just the IAC.

 

2 hours ago, Dee2 said:

 

Earlier you said that unplugging the MAF kept the engine running .  Have you replaced the MAF ?

Engine will run fine at idle without the MAF. Same with CTS and TPS. Now a MAF/CTS/TPS that is giving out the wrong values can cause it to fail to idle, but unplugging them the engine has a fallback. Unplugging the CTS makes the engine think it's at temperature(90C). Unplugging the MAF+TPS defaults it to a limp setting which is like fast idle. Unplugging the TPS or MAF uses a table to guess the other sensor.

Also unplugging them and have the engine run better doesn't rule out that sensor, the limp table is just designed to run the engine without care for power, emissions or milage. 

[Phil Hyde]

UPDATE: Replacement MAF did not produce a different result.

[Dee2]

15 hours ago, Phil Hyde said:

UPDATE: Replacement MAF did not produce a different result.

If unplugging the new MAF also allows the engine to return to normal then I would suspect the MAF wiring harness.

[GeneralDisorder]

Go back and re-read my post and follow the instructions. Troubleshooting with Visa will not produce the desired outcome. 

GD

[Phil Hyde]

1 minute ago, GeneralDisorder said:

Go back and re-read my post and follow the instructions. Troubleshooting with Visa will not produce the desired outcome. 

GD

I am aware of the troubleshooting that needs to occur and I do appreciate the suggestions.   I had already purchased a (used) MAF and there was certainly no harm in checking to see if it fixed anything.  I honestly didn't expect it to.

[Dee2]

49 minutes ago, Phil Hyde said:

I am aware of the troubleshooting that needs to occur and I do appreciate the suggestions.   I had already purchased a (used) MAF and there was certainly no harm in checking to see if it fixed anything.  I honestly didn't expect it to.

Seems like you've diagnosed the problem.  You can run the engine with the MAF unplugged.  That apparently eliminates the other variables. 

Was that a remanufactured one or a salvage?  OEM or aftermarket?

I've been down that path on my truck where I had to replace a bad MAF, got a remanufactured one only to find it was also bad. Long story short, I had to get a third one which finally solved my problem.

[Phil Hyde]

1 minute ago, Dee2 said:

Seems like you've diagnosed the problem.  You can run the engine with the MAF unplugged.  That apparently eliminates the other variables. 

Was that a remanufactured one or a salvage?  OEM or aftermarket?

I've been down that path on my truck where I had to replace a bad MAF, got a remanufactured one only to find it was also bad. Long story short, I had to get a third one which finally solved my problem.

Well... This one is a used OEM from eBay.  Sold as "functional".  So I am not sure I proved anything.  Either I have two bad ones... or it's not the problem.  Leaning toward the latter.

[Dee2]

1 hour ago, Phil Hyde said:

Well... This one is a used OEM from eBay.  Sold as "functional".  So I am not sure I proved anything.  Either I have two bad ones... or it's not the problem.  Leaning toward the latter.

Hopefully you have a 30 day return option. 

You can leave it unplugged for now and chase down whatever.  You may find other problems.  These are old cars.

 

PS: Did you ever check for any codes ?

Edited August 20, 2021 by Dee2
codes

[Phil Hyde]

1 hour ago, Dee2 said:

Hopefully you have a 30 day return option. 

You can leave it unplugged for now and chase down whatever.  You may find other problems.  These are old cars.

 

PS: Did you ever check for any codes ?

It was $50 shipped so I think I'll hang onto it.  Apparently a supply of extra parts is a good thing with these cars.

I've been a little pressed for time this week, but I plan on checking the codes this weekend.

[Phil Hyde]

On 8/20/2021 at 12:30 PM, Dee2 said:

PS: Did you ever check for any codes ?

Been working on other projects and finally got to focus some time on the Loyale.

I'm getting code 23 flashing.  So would I suspect either 2 bad MAF sensors, or perhaps faulty wiring?

  So

 

[DaveT]

Definitely check the wire and connectors.  I've seen wire break inside it's insulation inside the harness.

[Phil Hyde]

7 minutes ago, DaveT said:

Definitely check the wire and connectors.  I've seen wire break inside it's insulation inside the harness.

Does that harness go all the way inside the passenger compartment?

[DaveT]

The engine harness combines all the wiring on the engine, goes through 2 connectors to the harness on the body.  That goes into the passenger compartment. ..  kind of behind the fuse box.  Iirc, when I found the broken wite, I was using an ohm meter on the wire - one lead on the ECU connector,  one on the sensor connector.  Wiggling the engine harness turned up the area if the break.  I got lucky.