Missing and stalling

Topic: Missing and stalling (Read 7297 times) previous topic - next topic

Missing and stalling

May 04, 2012, 01:59:56 PM

Hello foxbody Thunderbird and Cougar enthusiasts. I'm a newboy here, I just got an '88 Thunderbird 5.0 with a 5 speed swap and only 82k miles on the odometer. I've been trying to soak up the knowledge that is here on the site (Lots of good info).

But I have a problem that I can't find a solution for: My Tbird has an intermittent miss that I can't quite find the cause of. When the engine is cold, it seems to run rather well, but once it warms up, it starts missing badly and will stall when I come to a stop, but it won't usually stall right away, it will run for about 10 seconds while stumbling, then just cut out. It always starts up right away afterwards though with no problems, and sometimes runs great again for about 30 seconds.

I pulled the codes, both KOEO and KOER show a code of 34, which appears to be an EGR sensor problem, but the EGR and the sensor both appear to be functioning correctly. I also checked the IAC, TPS, plug gaps, firing order, ignition wire condition, cleaned the salt and pepper shakers (which did seem to help, but probably isn't the cause of the problem), and searched hard for a vacuum leak, but found nothing.

Also, if I can trust the previous owner, he replaced the distributor, cap and rotor, plugs, wires, TFI module, PIP sensor, fuel filter, fuel pump, fuel pressure regulator, O2 sensors, and entire exhaust system. It's now running Factory tube headers, Mustang H-pipe, long glasspacks, and no tail pipe.

I'm starting to get stumped, and I'd rather not start throwing parts at it yet. Any idea on what the problem could be?

Missing and stalling

Reply #1 – May 04, 2012, 02:15:05 PM

Sounds like the way mine acts with my O2's hooked up....only mine won't start though.

If you've got a known good EGR, put it on, test it, and pull codes again, although there may be memory codes stored in the eec yet. I think it takes 40 engine start/off cycles to clear them once resolved. May be wrong...

BTW, welcome aboard!

Missing and stalling

Reply #2 – May 04, 2012, 02:50:22 PM

Thanks for the welcome, it's good to be in a place like this.

I don't have a known good EGR, I don't have many 5.0 parts sitting around. Although, I found an alternate definition for the code: EGR Valve Position/Pressure Feedback EGR Voltage Above Closed Limit. If that's what is happening, then my EGR sensor might be shot. The EGR did seem to close completely, but that doesn't mean the sensor is reporting correctly.

Maybe I need to unhook the battery to clear the codes before I trust that diagnosis too much though.

Missing and stalling

Reply #3 – May 04, 2012, 03:58:45 PM

When do you get the code 34? KOEO, Memory or KOER
You don't have a pressure feedback sensor.
You have a position sensor.
Code 34 says the sensor voltage is too high for the closed position.
If the code is KOER, disconnect and plug the vacuum line to the EGR valve.
Does the 34 change to a 33?
To clear memory codes, unplug the STI to SIGRTN jumper while the codes are reading out.

Missing and stalling

Reply #4 – May 04, 2012, 04:07:22 PM

Also, try running it with the spout unplugged. If it runs better with the spout out, it puts the computer into a fail safe mode that will ignore all but the most important sensors. You could also test several different things to test if its spark or fuel related.

Missing and stalling

Reply #5 – May 04, 2012, 04:11:35 PM

I saw the 34 code twice on the KOEO test, so I guess that means it was a hard code and a memory code. Then I saw it again on the KOER test.

I didn't think to try disconnecting the EGR, that'd be a quick test to show if that was the cause.

When I get home, I'm going to reset the codes and run the tests again to see if it reappears or reappears without the vacuum line plugged in.

Thanks for the ideas.

Missing and stalling

Reply #6 – May 04, 2012, 04:53:46 PM

Quote from: Haystack;388996

Also, try running it with the spout unplugged. If it runs better with the spout out, it puts the computer into a fail safe mode that will ignore all but the most important sensors. You could also test several different things to test if its spark or fuel related.

Will do. I don't think it really helped smooth the engine out when I was adjusting the timing, but I didn't try it for very long either.

Missing and stalling

Reply #7 – May 05, 2012, 12:02:57 AM

I reset the codes, run the KOEO and KOER again, and got the 34 code again right away. Then I unhooked the vacuum and plugged it, cleared and did the tests again, got the same 34 both times. Seems to me like the EGR position sensor isn't reading correctly. The big question is: Could this cause the missing and stalling I'm seeing?

I tried a test drive with the SPOUT removed, it ran almost perfectly. The only problem was some slight stumbles, but that might be from dirty injectors, as it has sat for a long time. What sensors does the computer ignore when the SPOUT is taken out? It seems like the problem is one of the deactivated sensors.

Missing and stalling

Reply #8 – May 05, 2012, 01:00:00 AM

Also, looking through my notes from the test, I had a code 21 fault from the KOER test. That's pointing towards a coolant temp sensor, which would make complete sense. If it were reading wrong when the engine warms up, it would be shoving extra fuel into a warm engine that doesn't need it. Also, I'd be willing to bet that the ECT is a sensor that is ignored when the SPOUT is removed.

Missing and stalling

Reply #9 – May 05, 2012, 02:35:07 AM

The ect will cause some codes and cause some other problems.

To be honest, I'm not completely sure what sensors are eliminated, so I'll look through some notes and see if I can find anything. Here is a "simplified verson of how efi computers work"

http://oldfuelinjection.com/?p=64

Here are some testing procedures to do when you have a no start condition. It is still failing to stay running right? If so, this should help you pin point your problem.

http://sbftech.com/index.php/topic,588.0.html

I would personally ignore the egr as long as you know it is in the closed position. As long as you have a code for it, the computer automatically deletes its function anyways.

Missing and stalling

Reply #10 – May 05, 2012, 02:43:07 AM

Also, run a blance test according to this. (Scroll down a bit)

http://sbftech.com/index.php/topic,2471.0.html

Missing and stalling

Reply #11 – May 07, 2012, 09:27:47 AM

I finally have time to update.

I did perform a balance test, the result was a 9, and there was no other clues that it was a specific cylinder related problem.

I tested vacuum with a gauge, I get a solid 20in at idle with the SPOUT out, and a wavering 19-20in at idle with the spout in. The vacuum changes seem to mirror the speed of the engine, so I didn't read too much into the non-steady reading.

I replaced the coolant temp sensor, it made sense and it did throw a code, but the new one didn't help the missing and stalling condition.

After all of that, I decided to double check my timing. I set it to 10degrees, then checked the timing with the SPOUT in for the heck of it, and that showed something interesting. The timing at idle with the SPOUT in is around 24 degrees according to my timing light, but it is not steady. When the engine feels like it's missing, the timing will retard by about 5 degrees, but then will go back when it recovers.

Is the timing the cause of my issues, or is it a side effect from whatever is wrong?

Missing and stalling

Reply #12 – May 07, 2012, 01:33:35 PM

Its normal for the timing to bounce around with spout in, even at idle. The sput basically allows the computer to change the timing.

I suggest you try checking the tfi, and spark output.

Put the timing light on your coil wire and see if it starts to miss spark while its running rough or missing. Does it do it with spout out at all? Just curious, not sure if it would even mean anything.

The ballance test tells us its not a fuel or compression problem, now we have it narrowed down to spark. Doing the tests in that sbftech link for a no start, you should be able to follow all of the testing procedures for no spark and go from there.

Let us know.

Missing and stalling

Reply #13 – May 08, 2012, 09:25:38 AM

Quote from: Haystack;389265

Its normal for the timing to bounce around with spout in, even at idle. The sput basically allows the computer to change the timing.

Ok, so the timing is probably changing because the engine is slowing down.

Checked the TFI, it passed all the tests with a Ohmmeter. Checked the spark output, I get a fat blue spark from the coil and from a plug wire.

Then I started going through the No Spark tests on the link, the only one that showed anything was when I put the light on the Negative coil wire and rotated the dizzy, the light dimmed. The test said if the light blinks, replace the coil, but I didn't git a full blink, just a dimming. Not sure if it's notable or not.

Then today, I set the base timing to 20 degrees, then removed the SPOUT. I wanted to be sure that it wasn't just the base 10 degree timing that was making the engine run well. On the drive to work, it still has an idle that is a bit rough and stumbling, but it never stalled and it never cut out at cruising speeds. That seems to tell me that even if it is a weak coil, it's not the cause of my cutting out and stalling.

I didn't have a chance to put the timing light on the coil with the SPOUT in and the engine missing, but it didn't miss a beat with the spout out and the engine stumbling at idle.

Missing and stalling

Reply #14 – May 08, 2012, 02:29:26 PM

As I was driving it today, I noticed something. I'm getting horrible gas mileage. I put 90 miles on this tank, and I'm nearly down to half.

That got me thinking... What if the problem is a clogged return fuel line? That'd cause higher than normal pressures at the fuel rail, would affect all cylinders, so it wouldn't show up on a cylinder balance test, wouldn't show up in the codes or on any electrical test I've been doing, and wouldn't have been fixed by any of the parts the PO installed. I'm not sure how the SPOUT would affect it, but it could be a contributing factor at least.

It makes sense to me anyways, I know the car has sat for a long time before the PO had it.