North American Turbocoupe Organization



Help with nailing down slight drivability problem.
KL Frye Offline
Junior Member
#1
My 87 TC is still experiencing a slight drivability problem where there is an intermittent miss while driving and an occasional struggle to pull past 4K RPM.

A little bit of background. Car has 44K original miles and is unmolested. Have known all but the last owners (4 total) personally. Last owner was meticulous with records, but did little maintenance wise and only drove the car 1500 miles in roughly 13 years.

When I first got the car last summer, it would not pull past 4K RPM- engine would build full boost, but would lay over like it was against a rev limiter or fuel was getting cut off.

I stored the car over winter and recently set about doing a tuneup in order to get a quality baseline from which to solve my driveability problem.

So far I have replaced:
Plugs- Motorcraft gapped to 0.034
Wires- Taylor Spiro Pro ( these wires have historically been as good or better than Motorcraft amongst our group that have ran them for 25+ years)
Cap/Rotor/TFI/PIP- all new Motorcraft Parts
O2 sensor- new Motorcraft
Timing Belt- new Dayco
Fuel Filter

One concern I had was that after all of the years of being a garage queen, that either the cam or tappets may have prematurely worn out, so I pulled the valve cover and both looked fine. I also pulled the IAC and cleaned it with Carb cleaner while apart, along with removing the injectors just to check their status while the upper plenum was off replacing the oil sending unit ( unrelated but it was fluctuating badly).

Put a fuel pressure gauge on the car and baseline w/o vacuum was 39 psi. While driving pressure would come up to roughly 45 psi under max boost.

I did all of the tune up items except for the PIP ( couldn't get the gear off myself)so I had a new dizzy that was supposed to have a new PIP in it, so I put that one in the car with the new TFI and the car ran decent, but still had the intermittent miss but was pulling up to redline. I pulled codes and got an erratic PIP code. Yesterday, I got the new PIP installed in the old dizzy and swapped it back into the car, reset base timing with spout out to 11 BTC, replaced the spout and drove the car.

Curiously, the tach got lazy between 3-4K rpm, like it broke or something. Also, and unfortunately, the intermittent miss was still there. After driving a few miles, the car start driving fine, but still had the intermittent miss. Without a load, the engine would rev freely to redline.

At this point, my only thoughts are either the coil- can't handle the demand, VAM - possible dead spot, or PCM are malfunctioning.

I would be indebted at this point on a direction to go in or something to test. My friend suggested pulling the VAM and making sure the contacts in there were clean and replacing the 28 year old coil. Aside from that I'm stumped.

Thanks!

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Pete D Offline
Administrator
#2
Have you checked cam timing since the new belt?

The coils are thought to be up to the job even on increased HP engines. Of course they can go bad but it doesn't seem to happen often and you can use any Ford coil from the era as a substitute including V8, V6 or regular 2.3

I would erase codes, drive it a few times and then see what comes back. I'd also run one or two cans of something like Seafoam through the tank (one at a time) to see if the injectors might need cleaning.

Pete Dunham


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KL Frye Offline
Junior Member
#3
I haven't checked the cam timing with the new belt. I didn't think the off and on issue would be affected by a cam off a few degrees. I surely can pull the cover plug and see how it checks out.

I do have some BG 44K in the tank right now to help clean the fuel system. I did replace the fuel filter as well amongst everything else.
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KL Frye Offline
Junior Member
#4
After doing some more reading, I discovered that the VAM also sends signals to the PCM that assist in determining timing. Would it be a safe assumption that a dead spot in the VAM would cause the engine to not want to pull through the 3-4K range?

Would a TPS with a dead spot do something similar and NOT throw a code?

Regardless, I'll be checking both with a meter next to either confirm they are fine or hopefully end this chase.

Pete, I'll get the codes erased, drive it and get back with you. I don't want to do something stupid and end up having to pull a head for a gasket or worse.
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Pete D Offline
Administrator
#5
I've had at least one case of a driveability problem that didn't set a code, nor could I detect flat spots in the TPS. Yet when I changed the TPS with a new one, the problem stopped.
Pete Dunham


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joejo Offline
Member
#6
where you located kl? I am in Indiana county near Blairsville. if you want to mee up we can toss some parts on it. I have a bunch of tc stuff. mine is currently under the knife too.
joe
88 tc
t3/4 50 trim stage 2 .48, bo 1.5 cam, lightly ported e6,stinger 3 inch ex., mild intake porting, basic cone filter, kirban, new motor (factory rods, .020 cp pistons, stock head specs).coolingmist injection, esslinger cam pulley.
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KL Frye Offline
Junior Member
#7
Gentleman, the issue was a coil. Replaced it yesterday and car ran great. However, I had a suspicion that the fuel pump is going bad and had the car shut off on me after some hard driving.
Joejo, I'm over in rural valley, but the car stays down near new Stanton.
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Pete D Offline
Administrator
#8
KL check your pms. Most likely a TPS from what your PM said.
Pete Dunham


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G-Rage Offline
Junior Member
#9
I'm bumping this thread to the top.
I'm the relatively new owner of Mr Frye's TC. I bought it a couple years ago.
The car still runs fine except that the problem he mentions about pulling past 4000ropm still exists.

if I slowly accelerate (low boost) it will smoothly go towards redline.
BUT, if I hit it with full boost, after 4000K rpm, I can feel it kind of go limp on power and sort of shudder. Hard to explain the sound.

is this the nature of the 2.3 to fall of the edge at 4K or possibly something else at play?
87 Black 5 spd, 47K miles, all original (minimally modified) survivor.
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Jeff K Offline
Administrator
#10
Hook up a fuel pressure gauge that you can see while driving. You should be able to rent one from a parts store if you dont want to buy one. You can tape it to the windshield so you can see it.

Go for a drive. Pressure should be 39 psi + boost pressure.... i.e., if boosting 15 psi, pressure should be 54-55 psi. If pressure doesnt go that high or even drops as boost and RPM go up, suspect a weak fuel pump, clogged fuel filter, or clogged filter sock at pump inlet due to rust in the tank. The stock pumps were pathetic when new, and get worse with age.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
11 Crown Vic Interceptor
14 Toyota Camry (wifes car)
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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