302 Ford Power lag

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  #1  
Old 08-27-11, 07:20 PM
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302 Ford Power lag

I have a 302 V8 in my 88 T Bird that has developed an annoying power lag at the point where the engine reaches a temperature of about 100 degress after 5 minutes of running time. Up to now, along with this power lag a slight vibration develops too. This lag lasts about 30 to 45 seconds and then goes away when the temperature hits normal on the dash guage. The engine runs perfectly after that, until it cools off, and then the process will begin again. Is there a sensor in the fuel system that could be bad, or is reacting to something that should be paid attention to?
 
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Old 08-27-11, 07:25 PM
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A choke problem jumps to mind. Don't remember what kind the old 302's had, but worth looking at.
 
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Old 08-27-11, 08:09 PM
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302 Ford Power Lag

Sorry, should have said no choke. fuel injected. 80000 miles, and I am the original owner.
 
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Old 08-28-11, 10:22 AM
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My bust, I should have figured it would be FI and not carbureted.

If your engine has a separate temp sensor for the computer (generally mounted near the thermostat housing vice the side of the block), that could be a possibility. Like a sticky choke, computer wouldn't realize the engine was warming up and could be running it too rich. O2 sensor, too, maybe could contribute to symptoms like that. Probably going to need to get a scanner hooked up rather than throwing parts. It has a standard OBD-I connector? Can't remember what the older Fords hookup looked like.
 
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Old 08-28-11, 04:19 PM
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as it's temperature related, I am seconding tow guy. O2 sensor. read codes.
 
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Old 08-30-11, 06:43 AM
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Thunderbird Power Lag

I think you guys might have it, but I thought an O2 sensor would trip a check engine light? I have a feeling that 02 sensor is going to be a trip to get to....
 
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Old 08-30-11, 01:02 PM
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hey, good I went back to this post. speaking of Fords...

I had 87 My Infamous Ford Taurus. It''d start and make noise like diesel engine, that will slowly go away, as it warms up. I drove it for a few years, always thinking, it was bad exhaust gasket. Until one night, I popped hood up for some reason, right after I started that car. To my horror, I noticed flame flashes on the firewall. Stuck my head all the way back there - well, m-f-er was shooting flames through exhaust manifold! I took it off next day, to find a web of cracks all the way through cast iron.
What will happen, on cold, those were shooting exhaust out. As it was getting hotter and metal expanded, it closed gaps.

you may simply have a leak somewhere. Throttle body, intake, whatever. Metal expands, closes gap, problem goes away.

Take a can of brake cleaner, with little straw nozzle. turn your engine on, and let it idle. give it cleaner shots, slowly moving around engine head, throttle, etc. if it chokes, you found your spot.
 
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Old 08-31-11, 04:50 PM
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Intake air temperature sensor located in the intake manifold, sends signal back to PCM regarding intake air temperature, which changes as engine warms up and cools down. Thus if it's sending improper signal, such as engine is already warm, when it's still cold, amount of fuel delivered could be less than what is required when engine is cold.
 
  #9  
Old 09-04-11, 06:44 PM
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302 power Lag.

Hooked up a code reader to the ECM and no trouble codes, but the fuel pressure was on the low side of a pressure test. Since I intend to keep the car regardless, had a new fuel pump installed. Engine runs a lot better thru the same heat range now but it still isn't where I think it should be. That temperature sensor mentioned looks like a prime target, unless 24 year old fuel injectors need replacing too. No expert, but I would think that a bad injector or multiple ones would operate poorly all the time. Is there a test for that sensor, or just replace?
 
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Old 09-06-11, 04:01 PM
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302 Ford Power LagI

I found the manifold air/fuel temperature sensor right under the distributor. I am going to replace that too. It wasn't even listed in the service manual diagram I have, and Autozone doesn't carry it. If this doesn't smooth out the low end of the power band, all it will leave is the O2 sensor.
 
  #11  
Old 09-07-11, 09:23 AM
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run 2 cans of Seafoam through a tankful at hwy speeds. basically, pour Seafoam in, flush it in with gas, and go on a fwy for 2 hrs or so, keeping her at 70.
if fuel pump improved it, but not all the way, it starts looking like clogged fuel filters, injectors, fuel lines, you know, that sort of things. Seafoam does magic in this respect.
 
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Old 09-18-11, 08:39 AM
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I have not done the Seafoam thing yet, but plan too. Is there a throttle body cleaner that can be used safely on this engine. I heard that Fords can be damaged with the wrong stuff. (I thought I found the air temperature intake sensor but it turned out to be the engine temperature sending unit for the dash temp guage. This was right under the distributor. I can see another sensor mounded in a tube that runs above the manifold, but that appeared to be carrying water to the thermostat. Is this the manifold air temp sensor? Would this not trip a check engine light and code?
 
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Old 09-18-11, 10:27 AM
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Originally Posted by WML13 View Post
I have not done the Seafoam thing yet, but plan too. Is there a throttle body cleaner that can be used safely on this engine. I heard that Fords can be damaged with the wrong stuff. (I thought I found the air temperature intake sensor but it turned out to be the engine temperature sending unit for the dash temp guage. This was right under the distributor. I can see another sensor mounded in a tube that runs above the manifold, but that appeared to be carrying water to the thermostat. Is this the manifold air temp sensor? Would this not trip a check engine light and code?
run 2 cans of Seafoam through a tankful at hwy speeds. basically, pour Seafoam in, flush it in with gas, and go on a fwy for 2 hrs or so, keeping her at 70.


YOU HAVE MY WORD Seafoam is perfectly safe. Have been using it for years, since 2001, on all our cars, in gas or in oil, even drove a Ranger with it in oil for 2000 miles, just to see what happens. it's made out of same stuff your oil and gas is made, hence it's perfectly compatible with any petrolate products. I use it in domestics, imports, large engines, small engines, old cars, new cars - never a trouble. All run like Swiss watch.
 
  #14  
Old 10-09-11, 06:07 PM
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1988 Ford 302 Power lag.

I did the Seafoam treatment, with no change. (Power lag appears after the Idle control motor drops the rpm from initial start up (1500 drops to 1000) put it in gear and drive a quarter mile or so and hope Im moving, not stopped at a light. I can drop it into neutral, and hit the throttle to keep it alive, or if Im already moving, I just hit the throttle and speed up for a short distance. Once I do that, the engine runs great, idles down to 1000 rpm and doesn't stall. It has a new TPS sensor, a new idle control motor, new plugs, rotor, cap, few pump, fuel filter that I installed. and it has been at the Ford Dealer for a week now. THEY installed a new ignition module and new wires, which obviously I didn't need as that made no change for THEM. THEY tell me this engine is too old for their test equipment. Why would an EEC IV system be rocket science? If punching the gas clears this up, logic would indicate a vacuum operated sensor or valve would be the target, but there are way too many of those for me to troubleshoot.
 
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Old 10-10-11, 08:00 AM
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Just wondering if you have gone over all the vaccum lines checking for any leaking, or collapsing under vaccum. Have they ever been replaced? Just wondering since so many other things have been addressed that likely were not part of the problem in the first place unfortunately.
 
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Old 10-10-11, 10:37 AM
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Ford 302 Power Lag

I have not found any vacuum lines that were of any issue except the one going to the pcv valve, which I replaced. No change doing that either. Remember that this is happening at a time when little vacuum is required. When I open it up, and CREATE a big vacuum, it clears up. I bet is is one of the valves that has one of the vacuum lines going to it that is sticking, and requires a hefty vacuum to open it now, but would open easily when in the warm up mode when it was operating correctly. (and why wouldn't the dealer have this knowledge in a computer/database?)
 
  #17  
Old 10-16-11, 05:34 PM
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I fd.dound the ECT sensor (Manifold Air Temperature Sensor) Tested it with an OHM meter and it followed the resistance scale (most to least as the temperature rose. That just leaves the MAP, and I have to borrow a hand held vacuum pump to test that. I will keep you posted
 
  #18  
Old 10-27-11, 07:17 PM
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When you open the throttle you lose vac.

Have you tried to leave the egr vac hose off and plugged. The egr valve may be opening and leaning out the engine at that temp.
 
  #19  
Old 11-06-11, 02:59 PM
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Ford 302 Power lag

I am writing to report that the Power lag in my 1988
T-Bird is no longer an issue. All of the lessons on testing vacuum and ohm readings are good, but there is no substitute for experience. I replaced a lot of sensors and components in the search for the "smoking gun" that would eliminate this aggravation, and it appears that a suggestion from MikeB early on was probably the first sensor I should have replaced, even though it tested fine with an ohm meter. The replacement of the Intake air temperature sensor and the MAP sensor pretty much fixed it. I would like to thank everyone who posted with suggestions, and since I know that google searches find comments in forums like this one for others, I would like to pass on what a great help the breakdown of the EEC IV system was in determining what sensors were active in the time/temperature window that this lag, and vibration were occuring. I replaced every sensor in the "window" except the coolant temperature sensor, even though none of them tested bad. I would part with the advice that if the vehicle is 22 years old and acting up, those sensors could be doing all kinds of thinking on their own, and you can eliminate a ton of frustration by just replacing them. My 302 doesn't sound like my hemi truck, but it sure runs sweet now!
 

Last edited by WML13; 11-06-11 at 03:01 PM. Reason: sentence structure
  #20  
Old 11-06-11, 04:08 PM
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Good job! Your persistence paid off.
 
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