Hesitation and lack of power when cold

[rideapony]

Hi all, I search for help regarding a hesitation and lack of power on my 1990 GT.
I have a TFS 306 and so far I've been troubleshooting this issue for a while. Here are some of the settings I currently have:

No error codes from EEC IV, stock injectors, new MSD wires, new ECT and ACT sensors, Throttle body plate calibrated at 1 1/2 turns after 0.010", RPM set to 850-900, new EVR, EGR and Idle control valves, TPS set to 0.98 V., clean MAF, and fairly new O2 sensors, good fuel pressure.

This hesitation and lack of power happens only when cold start after she reaches normal temp. runs fine, she even runs fine after 8 hours of being sitting while at work. Please help me finding what the heek is going on. The only things left will be fuel filter, fuel pump, and maybe a vacuum leak? But.....Only at cold start???

Please HELP ME.

Nick

 

[jrichker]

Possible open circuit in the O2 sensor heater circuit. The O2 sensors have a built in heater that only operates for the first minute or two. Use a voltmeter to look for 12 volts on the gray/yellow wires in the O2 sensor harness. You will need to the the key in the Run position but without the engine running. Make sure to check both O2 sensors for the 12 volts.

Also check to see that the orange wire that comes out of the engine fuel injector harness has a good ground. It is the ground for the O2 sensor heaters. You can ground it to the back of the cylinder head or to one of the intake manifold bolts.

Look in the lower center of the following diagram and you'll see the O2 sensor heater circuit.
Diagram courtesy of Tmoss & Stang&2birds

There is a fuse link up near the firewall where the main EFI harness enters the passenger compartment. The O2 sensor heater fuse link is in that area.


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 86-95 5.0 Mustang wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 94-95 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[rideapony]

Thank you jrichker for your reply.

I fixed the issue I was having with the EGR valve (Code 34) I remember I replaced the EGR plug because it was broken and I wired the new one following the chiltons schematic but the VREF (26) and Signal Return (46) wires in my car and at the EEC are exchanged!!! Based on this I corrected the wires position at the EGR plug and the problem is gone. NO MORE CODES. It cost me buying a Reman. computer under a "mechanic" advice so now I have 2 9L ECU's

Do you think by runing my car with those wires wrong for a long time might caused problems with the O2 circuit?

The O2 schematic says the the that the fuse link is by the strut tower I believe I've seen it.

Can I unplug the O2 sensors to check the circuits? Oh and I checked the sensors ground and is clean and solid bolted.

Thank you Sr. for helping our stang community

Nick

 

[rideapony]

Well I was sick for a few days and took me this long to check the O2 circuits and they're good. Checked fuse link by the firewall and it was good, then checked power and ground at the O2 sensor plugs and is all good.

She still shows the hesitation at cold start in the morning, timing is set at 10* so what else should I check?

I've been thinking about this other possibility and you guys let me know if I'm wrong:

Asuming that a possible vacuum leak is somewhere, is it possible to have a vacuum leak that happens only when engine is cold but when it warms up seals out because of the aluminum heat expansion? (Very weird thinking, ha!!!)

Ignition module fails when cold? Maybe should I just replace my NGK-5 plugs to see if any difference? Maybe another sensor that acts when cold start? I'm getting very frustrated but is hard me to quit and I might have to change the ECT sensor! Seeee? the frustration is already mounted because I shooting all over now!!!

Thank you for any other ideas that might help, Nick

 

[4G-KDMP]

I'd check for the simple things first, and a vacuum leak would be the first thing I'd check. From my experience a vacuum leak is more noticeable when things are cold .

 

[rideapony]

Thank you for the idea, I learned that a vacuum gauge really helps to determine the engine's health condition. In the Chilton book there are a few different vacuum gauge pictures with the different engine conditions like vacuum leak, not properly seated valves, etc.

Well using a gauge I found that the needle rattles a bit and the book sugests that I might have worn out valve guides. How in the hell is that? the heads are new with only about 2k miles and I haven't abuse her at all (yet). I just refuse to believe that.

More ideas will be greatly appreciated, thank you all, Nick

 

[jrichker]

Thank you jrichker for your reply.

I fixed the issue I was having with the EGR valve (Code 34) I remember I replaced the EGR plug because it was broken and I wired the new one following the chiltons schematic but the VREF (26) and Signal Return (46) wires in my car and at the EEC are exchanged!!! Based on this I corrected the wires position at the EGR plug and the problem is gone. NO MORE CODES. It cost me buying a Reman. computer under a "mechanic" advice so now I have 2 9L ECU's

Do you think by runing my car with those wires wrong for a long time might caused problems with the O2 circuit?

The O2 schematic says the the that the fuse link is by the strut tower I believe I've seen it.

Can I unplug the O2 sensors to check the circuits? Oh and I checked the sensors ground and is clean and solid bolted.

Thank you Sr. for helping our stang community

Nick

The O2 sensors and EGR sensors aren't related, so a problem with one system doesn't hurt the other.

You can unplug the O2 sensors from the harness and measure the heater voltage at the harness.

As you have learned, the computer is rarely the cause of code problems. It is almost always the sensor or wiring.

I am glad to be of help.

Joe R.

 

[rideapony]

Following the troubleshooting ideas I double checked the voltage at both HEGO connectors with the sensors unplugged and I have 11.6 Volts.

Searching thru the Stangnet forums for some of the same issues I have, some people say that the ign coil may cause some of those effects so I replaced the stock one with a MSD spare I had around but didn't see any improvements. This morning I had the same....

a) At cold start, she starts fine and idles about 1200 for a few seconds then drops to about 750 and some hesitation and then at normal temp she stays at about 900 - 950 rpm.

b) After cold start, when I start driving and shifting to 2nd while start pressing the peddal she starts hesitating and feels like doesn't develop hardly any RPM and then if I press harder there is a throttle response delay and then will suddenly accelerates and takes off but when I release the peddal to shift to 3rd I can hear and feel a POP (backfire) in the right side of the exhaust by the muffler or just before. The only way to avoid the POP (backfire) is to accelerate very gently while going thru 2nd, 3rd, and 4th. After that she runs fine.

c) This series of events Only happen at a cold start. Once she reaches normal temperature idle stay at about 900 - 950 rpm. From time to time I notice the same throttle response delay when start driving after being sitting for 8 hrs at work.

So more or less this problems happen when coolant temp is low...Any other ideas? Can the O2 sensors go bad without saving any error codes? What else should I look into???

Thank you for your help and suggestions, Nick

 

[caduck]

I have the same issue as you, Mine started when I had the AOD swaped for a t-5 and only happens when cold. My o2's are about 2 years old. I have no idea what the shop touched when they did the swap so could be a bunch of things to check. I will be paying attention to this post to see if you found the problem.

 

[rideapony]

Mine always has been a 5 spd and my O2 are not that old either (Maybe it is because they are not Motorcraft and they just go bad too quick????)....But no error codes???

Now it is coming to my mind that I used to have these same issues when I had my stock engine and I believe it was worst back then but I just don't remember how those problems went away. WTF!!!???

Any ways let's hope and wait for help from someone helps so we can clear those issues.

Nick

 

[jrichker]

Testing the O2 sensors 87-93 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

 

[ID89GT]

My car had similar problems to this. You start it up first in the morning and its really bucky and such but when the car warms up its just fine? Its probably a vacuum leak. My teacher taught me about this one.. I guess Ford has a very good adaptive system so as the car warms up it adapts to the vacuum leak and makes everything happy, which makes it seem like you're just fine. The leak is still there, its just the computer has made adjustments on it to make it run normal. Just what i've learned off past experiences with my car and at school.

 

[Lawbreaker5.0]

this is funny..(not really), but my car is doing the same thing, back firing, hesittation, all of that, even exactly about having to lay off the throttle. but mine also has surging idle once she is warm.

i'm in the middle of converting to 5 lug, so i can't say i know what the problem is, but i had a good size leak (and still might) cuz i haven't started her up with fressh oil, from the lower intake gasket. i thought it was a rear main seal for the longest time.

this all happened after i put on the TFS top end kit.

i should be done with the conversion in the next week or two, so hopefully i'll find out if that was the problem.

 

[87GT40]

i have the same problem minus the backfire. i know my rear main seal needs to be changed. i just changed the oil and went with a heavier oil and put some stop leak in it. the only thing mine just started doing this about 6-8 months ago. i guess i will check the o2 sensor voltage like mentioned before. i know a good way to look for a vacuum leak is spraying starting fluid in different spots to pinpoint it.

 

[rideapony]

Well I'll have to search for a vacuum leak after I check the O2 voltage at the computer connector. I'll be really pist off if it is a vacuum leak since I was very carefull when I installed the lower intake, even I used the gaskets with a steel shim in between as well as ARP studs to fasten the lower intake.

I had a bad experience twice with the cheap gaskets so I went even further trying to solve those leaks, and to tell you the truth I already sprayed WD-40 around the lower intake and couldn't find nothing abnormal. So I have no idea where to search now

Nick

 

[87GT40]

i had a vacuum leaj at that same area. between the lower intake and head. that was a while ago now. there was definetely some time between the leak and this prob now.

 

[jrichker]

If you got 11.6 volts when checking the O2 sensor voltage, you measured the O2 sensor heater voltage and not the actual O2 sensor output.

Your leak could be on the underside of the intake manifold and you would never find it by spraying liquid on the manifold mating joints.

NEVER, NEVER use flammable substances like carb cleaner, throttle body cleaner or propane to find vacuum leaks. Flash fires are definitely possible and becoming a crispy critter is not part of the troubleshooting process. Use some motor oil in a squirt can. The vacuum will suck up the oil and cause the engine to change speed.

 

[ID89GT]

Hey Jrichker, have you ever thought about making a smoke machine, like maybe a fog machine that you can funnel down to a tiny hose to pump into the intake to find leaks? I've always thought about making something like that, because our school had this machine that you would pump smoke into the intake and wherever there was a vacuum leak the smoke would come out of, It works really well and since you are the mastermind, was curious if you have ever thought of something like that

 

[rideapony]

I used a piece of tubing to hear around both intakes an then I put some oil around them and I found nothing, idle did not changed at all.

After those steps I checked the O2 sensors voltage at the computer connector pins 29 and 43 and I found they were switching from 0.1 to close to 0.9 Volts. based on those readings, are the sensors good?

As far as a smoke machine, I would like to make my own too

I remember when I had my stock engine I took her to a guy to find a vacuum leak (Like the one I might have now) and it works but the guy charged me about 60 bucks for like 3 minutes of usage!!!

P.S. I just went outside and checked the voltage athe O2 sensors connectors and found a steady 0.13 - 0.14 Volts. at idle, And I found another issue.

Some time ago I posted a thread about a vibration at high speed. I went thru some troubleshooting including drive shaft balance, new u-joints and new ford racing 3.55 gears but the vibration still there obviously it feels less but still. While checking the O2 voltage I was hearing this loud knockingg/bumping/chattering/grinding noise inside the bell housing, it seems like there are some clutch issues. I have a fairly new Spec-2 clutch which apparently is a POS.

So here we go another issue added to existing ones!!!!
Now what clutch to use!!?? And please keep bringing more ideas and suggestions for the other problems!!!


........Any other ideas or suggestions???

Thank you all, Nick

 

[jrichker]

Hey Jrichker, have you ever thought about making a smoke machine, like maybe a fog machine that you can funnel down to a tiny hose to pump into the intake to find leaks? I've always thought about making something like that, because our school had this machine that you would pump smoke into the intake and wherever there was a vacuum leak the smoke would come out of, It works really well and since you are the mastermind, was curious if you have ever thought of something like that

I learn new things all the time on Stangnet, and this is one of them.

The closest I ever came to something like that was to loosen all the rocker arms until all the valves had no pressure trying to open them. Then block off the TB with a PVC cap and pressurize the intake with compressed air. Then you use a liquid detergent and water mix poured over the intake manifold. Where ever it bubbled was your vacuum leak. Listening for air coming out of the oil filler on the rocker cover clued you in that the leak was on the lower side of the intake manifold...




rideapony: your first set of voltage readings from the O2 sensors look good. The second set don't look nearly as good. What did you do different between the first set of readings and the second set of readings ???