I have an 84 Tbird with 3.8L that has weak acceleration. I replaced the ignition module some time ago after it began cutting out on the highway, and this corrected that issue but still not running correctly, with the weak acceleration. I replaced the dist cap and rotor, and spent a while playing with the timing, but no improvement. The car starts and idles fine. Anyone have suggestions? The car has 76000 miles, also has newer spark plugs, plug wires.
Thanks a lot!
Russ
Plugged fuel filter or catalytic converter?
Thanks. I replaced gas filter perhaps 10k miles ago. Any way I can evaluate for possible restricted cats without just replacing or punching out the catalyst?
Try this vacuum gauge test.
https://www.youtube.com/watch?v=d-jp1IIJVVk
If your vacuum gauge is also a pressure gauge, you can remove an O2 sensor and jury rig up your gauge to measure the back-pressure at the O2 sensor hole.
How much pressure should be seen at idle at O2 sensor hole?
The closer to zero the better. Around 2-3 psi. I'll check to see if the shop manual gives a number.
The Shop Manual doesn't give a back-pressure number. Only gives the vacuum gauge numbers.
vacuum at idle 16-21 inHg. After revving engine to 2000 RPM, if the vacuum settles to below 16 inHg , you have a blockage.
Thanks. I checked it and found no issue. I did note that vacuum was 16 inches at idle. I subsequently found that my static timing was set too retarded, and after advancing a few degrees beyond the factory spec, it ran a great deal better. Thanks for your help! The only lingering mystery about this car is that since I bought it, about every year, it begins to run poorly and I reflexively replace the ignition module which fixes the issue. I have put 3-4 modules on this car in 20K miles. borg-warner. Back in the 1990s and had an 84 cougar and 86 tbird with the 3.8L, which I drove each over 100k miles, and replaced the module once on each car, so I dont know what is up with this....any thoughts?
I don't know about the quality of current replacement TFI modules, but heat has been the traditional killer of the ignition modules. The modules will naturally overheat during normal usage. This is why thermal grease is used between the TFI and the distributor, to conduct the heat away from the TFI.
If the engine is running too hot, the distributor will be hotter and conduct less heat away.
You don't say how retarded the base timing was, but running retarded can cause overheating.
Have you ever run the self tests to see what error codes you may have?
I haven't. I have not been excited about counting the flashing light or whatever it is that is needed to pull codes. Is there a code reader that can be purchased for this system?
https://www.amazon.com/INNOVA-3145-Ford-Digital-Reader/dp/B000EW0KHW/ref=sr_1_1?ie=UTF8&qid=1487889780&sr=8-1&keywords=ford%2Bobd-i%2Bcode%2Breader&th=1
For the money that's a nice reader, I bought one back when they were sold by Equus, that was before OBDII came out...
Once in awhile it'll lock up but removing battery resets it...
Do I need this extension cable??
16 inches is still PRETTY low for a stock engine at idle. At 16 inches on a speed density car, you'll be spraying more fuel. If you're getting incomplete combustion as a result of this you could be melting down your cat. Don't rely on a vacuum test for backpressure, check it directly with a gauge. On WOT snaps, you shouldn't exceed 3 psi. Obviously lower is better. You can also compare the temp of the pipe both before and after (with an IR thermometer) the cat to get an idea of the cat's efficiency, though without a downstream HEGO like on an OBD2 car, you're only getting a basic picture of it.
Thanks. Yeah I drove the car tonight and it runs OK but still something isnt quite right. I took on a 10-15 mile drive, and is still somewhat whimpy on highway entrance acceleration, and hesitates with acceleration occasionally (I know this is a chronic, common problem with these 3.8L motors as I had with my other two cars back in the 90s).
I ordered the scanner.
Well, I got the code scanner, and gave me 23, 84 (I have EGR vaccum line plugged), 13, 63. I ordered a throttle position sensor. I assume this sensor malfunction could cause the issues that I have had (LOW POWER, hesitation, stall at idle)??? Thanks alot.
Yep... When the TPS failed on my '93 Lightning it had about same power as a 6cyl with two bad plug wires...
Cool thanks. This low idle speed code, is this related to tps or something else?
In their diagnostics Ford says repair first code given then recheck, often additional issues are corrected or maybe other code(s) were just phantom in nature...
Yup 16" at idle on a stock 3.8 V6 is low. It should be around 20" at idle. My Thunderbird (mods in signature) makes 17" at a 700rpm hot idle. A stock 5.0 HO makes around 18-19" at hot idle, and a 5.0 SO makes around 20" at hot idle (from what I've measured over the years).
Intake Leak? From my past experience with these motors, my engine has zero blowby up in the air cleaner housing, which tells me that the cylinder bore/ rings are still in good shape. Vacuum lines are original but Ive found no issues on visual inspection. Thanks.
Fix the TPS code, then if still a issue worry about low vacuum... My bet is most of you problems/codes will be corrected...
Finally got a motorcraft TPS from rockauto. Ill let yall know howshe runs.
Hello go figure, I think I need a starter solenoid....I replaced TPS, and wen to start, and got nothing except cabin lights went out when trying to turn over, but no click. I charged battery, and still does the same thing. Sounds like solenoid no??
My first step would be to pull the small red wire off the solenoid and stick my meter on the wire.
See if you have battery voltage when you try to crank.
Voltage: solenoid
No voltage: neutral safety switch or ignition switch. Make sure you are in park or neutral.
NO.... Not likely if cabin lights are going out, you're dropping voltage and solenoid would have to be dead shorted to ground which is going to burn up battery cables... My bet is the battery didn't charge or is bad...
I have had this check your battery cable earth's and live track them back and clean and have a good look at the battery terminals sounds like a bad connection breaking down under load.
oops, my bad. I missed the "cabin lights going out" when cranking part. That kinda proves the solenoid is good.
I'll second this, but all the suggestions are good.
I put on a charger yesterday and initially pulled some decent current, but charged within a few hours (amperage dropped to < 1). I just drove the car 2 weeks ago, and pulled negative terminal a few days after parking.
Interestingly, in order to get cabin lights to come back on, I need to pull negative terminal on battery and reinstall.
If you have a jump lead connect the battery as normal and put one end of the jump lead on the negative (ground) Terminal the other end to the block.the problem is probably where the cable joins the battery connector .i cut the battery connectors off and replaced problem sorted.
Thanks all. I took off negative terminal and cleaned copper wire with sandpaper and car started. I ran KOER and got code 48 (in addition to EGR codes bc unplugged). Whats this?? Car still seemed sluggish on accel.
vane air flow high at idle.....what does this mean???
Means ECM is giving phantom codes or the scanner missed/doubled a pulse, the 3.8 doesn't have a VAF...
Ok. It's code 48. Is this correct interpretation of this?
I don't have my manual in front of me, but 48 seems to be "'air flow high at idle". No mention of VAF.
I'd think 16" of vacuum would trigger that code since a large vacuum leak would cause decreased engine vacuum at idle.
code 48 also relates to electronic ignition- coil primary circuit failure.not sure if it means its dead(no start) or out of spec(poor performance).might be worth looking with a volt meter.
The EEC IV error code charts are a composite of many different years and engines. Unfortunately that means you have to be able to weed out the definitions that don't apply to your vehicle.
The 84 Shop Manual groups KOER code 48 with the "Fuel Control" codes. There nine other codes that fall into this grouping.
The "pinpoint tests" only check the O2 sensors and the fuel injectors. The two EEC related things related to Fuel Control" problems.
Since the O2s have specific codes 41,42,91,92 lets rule them out.
Check the fuel pressure: Engine running pressure 35-45 psi. Turn engine off, pressure should hold at 40psi ±5psi for 60 seconds after key off.
With engine running: Unplugging each injector one at a time should drop rpm at least 150 rpm.
Your KOEO code 84 indicates a bad EGR vent solenoid. Curious what led you to unplugged the EGR vacuum line?
When you checked the vacuum at 16in at idle did you then rev up to 2000rpm to see if it would hold at 16 at the higher rpm?
Thanks a lot. Yes the vacuum did hold at higher revs. I plugged the egr for the heck of it a while back to see if it helped with hesitation. Thanks for the help.
The rest of the stuff related to Fuel Control error codes. As for which ones could cause a code 48, your guess is as good as mine.
Where is the line access to check fuel pressure?
Schrader valve in the top of the CFI. It will have a valve cover on it.
Im confused about these fuel control codes. Does this mean that the ECM, and sensors are not the issue but some other item is causing A/F ratio to be off? In other words, based on what output is the code 48 being triggered?
Also, to access the valve on regulator, do I pry it off? Drill?
Me too.
That seems to be what it means. Although I'm not sure that would totally rule out the ECM being bad.
Well the O2s would indicate whether the A/F ratio is out of specs. Since you have no O2 codes, the only other thing I can think of that the ECM could be looking at is the engine RPM.
The ECM controls the RPM by controlling the throttle position and the fuel injectors. (Of course you shouldn't have your foot in the throttle while the tests are running)
Take the air cleaner off. Unscrew the cap off the valve on the drivers side of the CFI.
Fuel pressure check.
haha, oh yeah I forgotten that this nipple sticks out in plain site.
Well, I took for a drive and it runs pretty well. I suppose I will just ignore those fuel-related codes.....
As it turns out, the car runs much better with new TPS, but still doesnt have good power. Hesitation is gone. I will pursue these other checks.
That was a feature built into the 3.8 from the factory. ;)
Lol agreed the motor is gutless on a good day, but I'm pretty sure this thing is not making 120hp. It's pretty sluggish merging onto the highway.
0-60 in around 10 seconds? Quarter mile in about 17 seconds? Those are the normals for the 3.8 in these cars.
Yes. I am aware but still am pretty sure something is wrong. I had and 84 and an 86 back in the early 90s which I drove gen of thousands of miles and don't recall them being so weak. I've had this car for 3 years but don't drive it much. Maybe I'll time a 0-60 run but I bet it's longer than 10.
Have you checked the timing chain for play if it's stretch too much will throw the valve timing out enough to lose power,compression test? and how old are your o2 sensors may still be working but get slow at responding changed mine very pleased with the result but never threw a code.
O2 sensors are original. Timing chain is too but I know that both of my 3.8 from back in the day had over 100k on them and we're very worn out motors but ran stronger than this motor which has 70k miles, has no blow by evident in air cleaner housing?".