Hesitant Under Load

[SourceB5]

'91 GT with 22k original miles. Stock with the stickers in the window ( pretty much)... So I started her up for this summer and she was even hesitant to start. The starter motor sounds like it is starting to go. No biggie. Car starts and at very first is a little rough. Warms up idles pretty much fine. Now under very light load it's fine. If you try and hit the peddle any harder then lightly it Boggs as if you were blipping the peddle.

Worked on many of cars and am pretty mechanically inclined. I replaced all the plugs. Checked all resistance on the wires. All are between 7kohms and 12.5kohms which to my understanding is fine. Changed the fuel filter. Ran some seafoam thru the vac lines. I replaced the coil thinking it was that. Pulled the distributor cap everything looks brand new. Adjusted the timing... Car stock says should be at 10 deg btdc. Runs better at 12 deg so I left it at that. I ran the codes. Got 41 and 91. O2 sensor issues running lean. Checked the cylinders and cylinder 7 thru a code. I double check that plug and wire. Also hooked up my thesescope and listened to the injector. Audibly it sounds likes it's cycling just like the rest so I have yet to swap or replace it.

Any other thoughts please chime in? Did I mention I need to replace the throw out bearing and pilot bearing because they sound worm possibly from just not being used often enough.

 

[stykthyn]

Change your o2 sensors.

 

[SourceB5]

Change your o2 sensors.

Would this cause the motor to run rough? Wouldn't think so, but yes when i pull the tranny to swap clutches and such I will be changes the o2 sensors.

 

[stykthyn]

You pulled an o2 lean code. These things do go bad and yes they can be the cause of many poor running conditions.

 

[SourceB5]

Don't mean to bring this back a few weeks later but I've been working on a few other maintenance things that took a while. I replaced the clutch, pilot bearing etc. Also did breaks and such.

While I was under the car i replaced both o2 sensors. Hoping that would be the fix, I started her back up after all said and done. Car still stumbles to life with the turn of the key. Once it's on the idles very run, down to as low as 300 rpms up to 1300 Rpms. Will recheck the codes. My next steps are to check fuel pressure. Then replace the MAF. Even after cleaning it, I'm sure it could just be "bad".

Any other input?

 

[SourceB5]

Brakes

 

[jrichker]

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 134,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

 

[SourceB5]

Printed this already and started checking things off of my list. Just curious to see if anyone else had similar issues... Seems as though every issue from the checklist is just parts of my issue, either it has a hard start while cold, or while hot or rough idle....

I'm having a rough idle, stumble to start whether really cold or hot, and cylinder 7 code thrown without any other codes now. Cylinder 7 seems to check out as far as the fuel injector, plug, wire etc. Will test for full compression (which could still be a posiblility that say the valve is on its way out) I just cant imagine since the car only has 24k miles...

But yes thanks for putting together that Checklist!!!!

 

[modulistic]

Injector or injectors may be gummed or plugged, especially since it is appears to sit for most of the time. if it was me, I would swap that #7 injector to another cylinder, and see if the code follows the cyl or stays on 7.

 

[SourceB5]

Pulled the maf, throttle body, IAC, EGR, upper intake manifold off the car today. Cleaned every part involved. Pulled the injectors and cleaned all 8 of them ( they came out looking mint... ). Bolted everything back up, and no difference car ran exactly the same. Ran the codes and now instead of 41,91 I'm getting 42,92... And code 18 came up as well, not sure why. While I was running the engine on running codes, the car went from a rough idle to actually running perfect, as if the car was 100% normal. Once I disconnected the jumper boom back to running really rough, maybe even worse then before. Runs likes it's misfiring a cylinder. When you tap the gas it takes a second to raise the Rpms. Nothing is smooth. Will post a video next. Start up also worries me. Cold or hot, the car has trouble starting. It literally stumbles to life. Also get a code for cylinder 7 in the imbalencing test.

Any other ideas ?

 

[jrichker]

Compression test results for all cylinders, especially #7?

 

[SourceB5]

Will be posting the results tonight. Thanks!

 

[SourceB5]

Cylinder compression test.

1-176
2-180
3-176
4-177
5-172
6-172
7-170
8-173

 

[jrichker]

Cylinder compression test.

1-176
2-180
3-176
4-177
5-172
6-172
7-170
8-173

The compression test looks really good.

Note on the cylinder balance test:
If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1400-1600 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

If you swapped the fuel injector positions when you put the injectors back in, you can eliminate the actual injector as being the problem. Any problems related to #7 cylinder must be injector wiring or ignition related.

.

 

[SourceB5]

I did swap injector #7 with Injector #6 when I pulled each off to clean them and it was still giving me the Cylinder 7 as having issues on the balance test. therefore i ruled out the injector as being an issue... as for the injector wiring, I assume this could be an issue. I will put the tester on them tonight. What should each injector be reading as say idle 800~1000rpm?

As for the IAC/IAB, I think it would be safe to assume that the unit could be NO GOOD? I pulled it off, cleaned it and the actuator seems to move smoothly... Maybe some other issue with this unit?

The only options I feel that I have right now is to replace single items one by one until I find the issue, for example, the IAC, MAF, TPS.... Because I pulled each off, cleaned them thoroughly, even tho they looked and seemed to function like brand new.

 

[SourceB5]

So I put in a new IAC... Car started funny as usual, stumbling to life, decided to readjust timing and make sure that it was at a good spot. Have it at like 11~12 Deg and it was idling great. As if the IAC was part of the issue. Decided to take it around the block... Boy oh boyyyy, first, second and third gear popping and throwing me around in the drivers seat. Came home and happened to stick my head by the rear end of the car, and I hear a humming tone coming from near the tailpipes. Would this be the fuel pump humming? Assuming this can't be good but unsure. Sounds like a high pitch electronic hummm.

Shut the car off, turned her back on and man took me like 20 cranks, stumbles to life, sounds like its running on 4 cylinders, stalls. Again, again then starts to come back to its normal 8 cylinders, and runs rough but at least runs. Ran as if the SPOUT was doing the wrong thing to the timing (meaning sounds like the timing was off... Didn't recheck it yet but clearly tightened the distributor so can't imagine it would have somehow changed)...

So not to throw another wrench into this but could the fuel pump be on its way out? Tried testing fuel pressure the other night but for some reason, not sure why but my gauge wouldn't read the pressure correctly... I primed the fuel pump multiple times and throw the gauge on while the car was off. Does the car have to be running why testing pressure from the shredder valve?

 

[SourceB5]

Startup, and like the description says, this is a better startup then usual... Typically it stumbles to life at like 300rpm and either stalls or eventually comes to a wild 1000rpm idle.


View: https://www.youtube.com/watch?v=0kEL6PYcETQ&feature=youtu.be


If you turn up the speakers and listen closely, this is the hesitation when in neutral (not driving)... you can hear the hesitation when I get on the gas and it sounds like I'm tapping the gas multiple times quickly... When really I'm putting the pedal down say half way or more and then lifting off. Its not smooth at all like it should be.


View: https://www.youtube.com/watch?v=UC0Vom-Omrw


Better videos to come if warranted. It just sounds like when I press the pedal, the Air Intake is sucking air then the rpms finally raise slightly... Also, If I were to mash the gas and really try and bring the rpms up... I highly doubt I can hit anywhere near 5000rpm or higher.... It has no power and hesitates.

HICKUP is maybe a better turn.

 

[SourceB5]

Not to post yet again but am finished up in the garage for the night... After adjusting the timing for a final time and resetting base idle, I am convinced that the IAC was part of the issue. The car idles very consistently now. Holds 700rpms great at idle.

That being said, it still is very hard to start cold or hot (more so when hot), and really hiccups when given a heavy throttle. Those are my consistent issues right now.

 

[SourceB5]

The tool I've been waiting for has finally come in and coincidentally, today I was reading this thread:

http://sbftech.com/index.php/topic,36384.60.html

Everything that has been happening and everything that he has completed, fixed, cleaned fits my story. Basically long story short, I tested the Fuel pressure with my gauge and am reading 6psi... The fitting fits well, no leaks, not sure how the car can even run on 6PSI yet six... But I'm confident that it is the Fuel pump. Anyone else like to chime in please do so? I will be dropping the tank friday to start this fix. I will keep anyone interested updated on my findings.

 

[SourceB5]

In case this has happened to anyone else, I have solved the issue... I dropped the tank and replaced the fuel pump.

Turned the car on, reset base idle. Adjusted Timing a few times and boom the car runs like a it did out of the factory. Fuel pump now pushes 40psi like it should... No problem with starts (hot or cold), no hesitation or stumble to life. A very sleigh hiccup when your go WOT in neutral (not sure maybe this is normal???)

Hope this helps anyone else.