Rough idle - could use help diagnosing

[A4x4Junky]

Hey everyone…having a bit of an issue with the engine in my 67.

The engine is a used 351W out of a 94 Lightning with fuel injection from an 89 Mustang.
No emission equipment on/hooked up.

Engine starts right up, but shakes a little and runs rough. Exhaust smell is pretty strong. Engine will occasionally stall.
If it stalls, it starts right back u p.

I did a little looking around on the internet and tried to take care of a couple things people said could be an issue.

I was told a dirty MAF could cause issues like this, so I followed the directions to clean it. No difference. Was also told to check voltage at the sensor, and although I cannot remember the number I got, it was within spec.

I was told an improperly adjusted TPS could cause these issues. It is currently sitting at .96v at idle.

I was told to check vacuum…holding at about 17 at idle.

Checked fuel pressure at idle and it was in the mid 30s. Changing vacuum to the regulator also changed fuel pressure.

I decided to pull the 4 plugs on the passenger side of the engine (because the driver side looked like a pain in the butt). Number 4 looked brand new. No brown/tan on the ceramic and no smell of gas. 3, 2, and 1 all looked normal. Tan on the ceramic…so I tried to follow this lead.

Pulled the passenger side valve cover to make sure all rockers were tight and moved approximately the same amount while cranking. Everything looked great. I ran a compression test on cylinders 3 and 4 just for comparison and both came back at 160lbs. This made me feel a little better. Swapped in another plug (didn’t think this was the issue, but wanted to try) and it made no difference. I swapped in another plug wire, no difference.

I was pretty convinced that it was a fuel issue…so off came the upper intake and fuel rail. Pulled the #4 injector and hooked up a test wire. 12v and ground to the injector and got a healthy click. Sprayed some throttle body cleaner through it and it seemed ok. Put it back together…exactly the same.
Checked resistance of two injectors (one from cylinder that was burning healthy and #4) and both were almost identical.

Next I checked the wiring to the injector. The red wire had 12v with key on. Other wire grounded by the computer. Checked continuity from the injector plug to pin 13 on the computer … worked as it should. Verified the computer would ground the injector with the engine cranking by hooking up a test light. That worked as well.

That is where I am at now.
Mechanically the engine seems ok. Compression test came back good. Good fuel pressure. Injector is being instructed to fire and it seems like it is…but I still don’t think #4 cylinder is firing.

Sorry for the book…but rather pissed/confused…mostly pissed at the moment.

Thanks,
Anthony

 

[pcf_mark]

Super low tech way to confirm you have the dead or weak cylinder: pull all the spark boots off at the cap and push them back on to just before they click. Start the engine and pull a plug wire off and see if the RPM drops (you can tell by the sound no tach needed). Once you try a cylinder put it back on and go to the next one. One or more will not decrease the idle and you know that cylinder is not working.

I would not trust the color of the plugs for that. Then start your trouble shooting with spark plug, wire. Then swap injector or injector plug (batch fire right?) to another cylinder and see if it changes.

 

[A4x4Junky]

Super low tech way to confirm you have the dead or weak cylinder: pull all the spark boots off at the cap and push them back on to just before they click. Start the engine and pull a plug wire off and see if the RPM drops (you can tell by the sound no tach needed). Once you try a cylinder put it back on and go to the next one. One or more will not decrease the idle and you know that cylinder is not working.

I would not trust the color of the plugs for that. Then start your trouble shooting with spark plug, wire. Then swap injector or injector plug (batch fire right?) to another cylinder and see if it changes.

It isnt batchfire, but I did swap injectors from one hole to another last night. Of course the last time I put it together I nicked one of the injector o-rings...so have to wait to put it back together tonight.

Anthony

 

[BUCKNBRONK]

Does it have a IAC valve on the throttle body? I know when they go bad it will make the motor run rough and rich at idle, cause low idle rpm and stalling issues.. Have u ever changed ur O2 sensors?

A few questions -
Is the issue only at start up/ cold temp.? Or does it run poorly at all times? Is it just running rough like its getting to much fuel( strong fuel smell in exhaust) or does it have a obvious miss in one or more holes? Is this a new condition or has it always been this way?

 

[A4x4Junky]

Does it have a IAC valve on the throttle body? I know when they go bad it will make the motor run rough and rich at idle, cause low idle rpm and stalling issues.. Have u ever changed ur O2 sensors?

A few questions -
Is the issue only at start up/ cold temp.? Or does it run poorly at all times? Is it just running rough like its getting to much fuel( strong fuel smell in exhaust) or does it have a obvious miss in one or more holes? Is this a new condition or has it always been this way?

The IAC is on the throttle body. I havent looked at that yet, though I do understand they can cause stalling issues.
The O2 sensors are brand new.
The problem is when cold or warm, makes no difference.
I would say it feels like a miss on 1 cylinder...Im guessing #4 from what I saw yesterday.
This has always been this way, but my always is only a couple weeks. Just got it running.

Anthony

 

[Viperwolf1]

Does the ignition firing order match the cam? Have you tried a KOER test along with a cylinder balance self-test? http://sbftech.com/index.php?PHPSESSID=3cd7df98fbd8967d86281fef41def3f3&topic=2471.0

 

[A4x4Junky]

Does the ignition firing order match the cam? Have you tried a KOER test along with a cylinder balance self-test? http://sbftech.com/index.php?PHPSESSID=3cd7df98fbd8967d86281fef41def3f3&topic=2471.0

I used the firing order from the engine (1,3,7,2,6,5,4,8) and did doublecheck, so that should be right.

I tried KOER before I took anything apart and four times in a row it stalled before it could finish and I ended up with no codes. I will certainly try again when I put it back together tonight.

Thanks for the help

Anthony

 

[12-Pack Jeff]

Do you have an adjustable fuel pressure regulator? If so, crank up the pressure to 40.. when I first fired mine up it was in the mid 30's and it ran rough too.. Cranked it up to 42.. smoooth

 

[pcf_mark]

Cylinder balance self test..I need to read about that.

When you check your firing order also make sure the distributor is turning the way you think it is. It will run rough but will run if you put them on thinking it turns the other way.

 

[Viperwolf1]

Shaft turns CCW.

 

[OX1]

I was going to suggest cyl balance test also.

My dads LTD passed the balance test 3 times,
but in frustration (cold start issue), I had inj
(stock 19's) cleaned/flowed and this is what I got.

Results---Before---After----Increase %
1--------46--------50---------9
2--------44--------50--------14
3--------45--------50--------11
4--------46--------50---------9
5--------41--------50--------22
6--------48--------50---------4
7--------46--------50---------9
8--------48--------50---------4

Amazing to me it did not at least pick up Cyl 5 in the
balance test. It may not be sensitive enough for
relatively mild flow restrictions. I would still try it though, but
it did not conclusively rule out an inj problem like
I thought it would/should.

If you don't figure it out, I have that EEC IV breakout box
I could bring down too.

 

[A4x4Junky]

Put it back together tonight with a new oring. Suspect injector has been cleaned Nd put in cylinder 2 just for a change. Fired it up and no change.

Hooked up the scanner and KOEO came back only with my disconnected emissions equipment. Finally managed a KOER scan which came back with the emissions equipment and a failure to control high idle ... which I suspect is due to the poor dining condition.
Followed this up with three cylinder balance tests. First one pointed at number 4. Second test pointed at number 8 which was a surprise. The last one pointed at 4, 5, and 8. Not sure what to make of that.

I am open for suggestions. My compression is good. My spark plugs are new as are my wires. I have swapped plugs wires and injectors from known god cylinders with no change. Fuel pressure regulator was new with ok pressure. Changed in the old regulator just in case. No change. Timing is set to 10 DEG BTDC. I was able to heat all 8 injectors clicking away with a mechanics stethoscope. I verified spark to the cylinder. Fuel, air, spark. Seems like everything, but still no good.

What am I missing?

Thanks,
Anthony

 

[hartbronco]

Did You look at the Cap and Rotor ? it could be bad , somtimes they are broken when You get them new out of the box .

 

[Viperwolf1]

One balance test will pinpoint cylinders that are a certain percentage out of normal for rpm drop. For example, cylinders 1-7 are cutoff and each one drops rpm by 100. Then #8 only drops rpm by 50. This indicates #8 is not contributing to engine rpm like all the others. There is a standard percentage the ECM uses to determine good/bad, maybe like 10%. If all cylinders were within 10% of the rpm drop, all would show as good. Successive balance tests cause the standard to tighten, maybe to 5% for example. This can naturally ID more cylinders as bad.

Could be something is not quite right with #4. Could also be something random like MAF out of wack. I think if a cylinder was bad it would be consistant in the test.

Just to be sure, what are the MAF sensor numbers and what size housing is it in? What about cam specs?

 

[ransil]

D
Clean the IAC and set idle

Idle reset procedure.

1. Unplug the SPOUT connector, start the engine and let it reach operating temperature, then check and, if necessary, adjust base timing.

2. Shut the engine down, then stick a .050-inch feeler gauge between the throttle stop screw and lever.

3. Disconnect the IAC solenoid connector, shift the transmission into Park, start the engine and allow it to stabilize for approximately two minutes.

4. Adjust the throttle stop screw as necessary to obtain an idle speed of 675 rpm 25 rpm.

5. Shut the engine down once again, then disconnect the battery for a minimum of five minutes to allow the PCM's keep-alive memory to time out.

6. Remove the feeler gauge, reconnect the SPOUT and IAC solenoid connectors, then start the engine and allow it to stabilize for two minutes.

7. Goose the throttle several times, let the engine return to idle, then make sure the base idle speed remains in spec.

8.Drive it for 15 minutes making frequent stops.

 

[A4x4Junky]

One balance test will pinpoint cylinders that are a certain percentage out of normal for rpm drop. For example, cylinders 1-7 are cutoff and each one drops rpm by 100. Then #8 only drops rpm by 50. This indicates #8 is not contributing to engine rpm like all the others. There is a standard percentage the ECM uses to determine good/bad, maybe like 10%. If all cylinders were within 10% of the rpm drop, all would show as good. Successive balance tests cause the standard to tighten, maybe to 5% for example. This can naturally ID more cylinders as bad.

Could be something is not quite right with #4. Could also be something random like MAF out of wack. I think if a cylinder was bad it would be consistant in the test.

Just to be sure, what are the MAF sensor numbers and what size housing is it in? What about cam specs?

Been away almost a month, but still banging my head against this problem.
I decided to check the MAF again...because I wasnt as sure about the readings as I should have been.

Turns out I had good grounds, and a solid 12v power...but the signal wire that should read .9 to 1 Volt at idle was reading over 3.
Honestly not sure how I missed that the first time, but happy I rechecked.

Got another MAF sensor and installed it. Started up and seemed to idle a little better. Let it run a couple minutes and it started getting rough again...

Tested this MAF sensor and I was reading just over 1Volt...so while changing this seemed to help a little, it did not fix my rough idle.

Reran the cylinder balance test...same results. 8 and 4 came back as problematic.

I have replaced everything I can think of on cylinder 4...yet it continues to be an issue. I have changed / swapped the plug, wire, and injector. I have verified the resistance on the injectors, verified that I have 12V at idle and that the computer is grounding the injector. I have about 160 lb of pressure on compression test and have tested for spark at the plug. This is really starting to piss me off.

Looked at the firing order and noticed that the two problem cylinders are next to each other on the firing order/cap. Started hoping that maybe the cap had a defect causing the two of those cylinders to misfire.
Picked up a new cap this morning and put that in ... no different.

I have not set the IAC as Ransil recommended, but will be doing that tomorrow...though it doesnt seem to be a low or high idle issue, rather a miss. It feels like a solid miss, but I dont understand why.

Could a leakdown test show bad results with a good and even compression test? Compression numbers are good, but Im willing to try a leakdown if it makes sense. I could just think that with solid compression numbers that the chances of a leakdown showing me anything would be slim.

Starting to think about the fuel system. Have a BC tank with intank fuel pump. Purchased the pump about 3 years ago, so dont recall the numbers, but do remember making sure it was capable of running substantially more horsepower than the 230ish this engine was rated for. BC steel lines to the 351W Lightning fuel rail. My fuel pressure gauge is missing the adapter to tie into the fuel rail, so I had to pull the guts out of the valve to run a pressure test. I believe I was about 38lb at idle. Is it possible to starve the two rear cylinders if my pressure/fuel volume is too low? Grasping at straws here...but looking for possibilities.

All electronics (computer and sensors) are from a 1990 Mustang 5.0
The cam is the stock lightning cam (I think...did buy the engine used) which I understand to be very mild.

Thanks again.

Anthony

 

[Viperwolf1]

Make sure 4 and 8 wires are not swapped on the cap. If the plug wire condition is questionable the spark could be jumping from those wires to another plug wire (if ran next to another) or to anything else that is grounded. Maybe swap those plugs and wires with 2 others and see if the bad cylinders move. If that doesn't work maybe swap the #4 and #8 injectors with 2 others. I can't believe anything is wrong inside with 160 psi.

 

[A4x4Junky]

Make sure 4 and 8 wires are not swapped on the cap. If the plug wire condition is questionable the spark could be jumping from those wires to another plug wire (if ran next to another) or to anything else that is grounded. Maybe swap those plugs and wires with 2 others and see if the bad cylinders move. If that doesn't work maybe swap the #4 and #8 injectors with 2 others. I can't believe anything is wrong inside with 160 psi.

I am pretty embarrassed to admit it, but I had the #4 and 8 wires crossed on the cap. I put it on wrong and didn't find it when I went back to doublecheck my firing order. Runs fantastic now. Thanks everyone for the help. I am thrilled that it was as simple as that.

Anthony

 

[OX1]

I am pretty embarrassed to admit it, but I had the #4 and 8 wires crossed on the cap. I put it on wrong and didn't find it when I went back to doublecheck my firing order. Runs fantastic now. Thanks everyone for the help. I am thrilled that it was as simple as that.

Anthony

Glad to see you are keeping it. You have way too much work in that
to let it go.