1988 Turbo Coupe Boost Problems

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1988 Turbo Coupe Boost Problems

March 11, 2017, 05:22:18 PM

Greetings,

This is my first post and I thought this would be a great place to do it. I have a 1988 Turbo Coupe with the 5 speed manual transmission. It has just over 93,000 miles. Lately it has developed a problem where it bucks and pops when boosting. The original vane air meter tested out of spec so I purchased a remanufactured unit. That was bad right out of the box because the car wouldn't even start and it tested out of spec. I returned that one and got another remanufactured unit. This one tests ok but the car is still doing the same thing. I even tried bypassing the boost control solenoid but no luck. I did get codes at different times in KOEO mode. One having to do with the vane air sensor and the other was vane air temp sensor. This unit tested ok so I don't know what's going on. Unfortunately all that is available are remanufactured units. Could the ECU or a bad wastegate be causing this? Have any of you had this problem? I like the car but it's not drivable and I'm getting annoyed. Please, if anyone can help I'd really appreciate it. Thanks.

P.S. The car drives well enough while not in boost but as soon as it reaches 5 psi it starts acting up. I won't drive it at all until I can fix it, if I can fix it.

1988 Turbo Coupe Boost Problems

Reply #1 – March 11, 2017, 07:45:01 PM

I would check fuel pressure first, mainly because it's free to check. It should be around 40 with the vacuum line off. I suspect it is going to be an ignition issue. I would check the condition of the plugs, wires, coil, and maybe the TFI.

1988 Turbo Coupe Boost Problems

Reply #2 – March 11, 2017, 08:23:02 PM

Thanks for the response. I recently replaced the plugs, wires, cap, rotor, coil, fuel filter and air filter as part of regular maintenance. I do have a fuel pressure tester, I just have to find it. Please pardon my ignorance but what is TFI?

1988 Turbo Coupe Boost Problems

Reply #3 – March 12, 2017, 10:54:37 AM

Did the problem start after you replaced the ignition parts? What did you use as replacement parts? Plug gap?

The TFI stands for thick film ignition. That's what Ford calls the ignition module on the distributor.

1988 Turbo Coupe Boost Problems

Reply #4 – March 12, 2017, 10:55:38 AM

TFI= Thick Film Ignition. The module mounted to the distributor.

Did the problem exist before your maintenance or did it start after? Just a suggestion....Unplug the VAM and go for a ride in limp mode. See if behaviour is the same, keeping in mind limp mode won't run all that smooth.

Bucking and popping is usually a sign of a lean mixture or over advanced/bad ignition. I would start by making sure your base timing is set at 10* BTDC spout out and advances to around 25* BTDC with spout in.

Check that you have the plug wires fire order in correct sequence.

Make sure your plugs are gapped properly....I believe stock is 0.034.

These cars are finiky and dont seem to like parts store Ignition components. Stick with Motorcraft.

Look for vac/boost leaks Make sure the Vam Hose is crack free and is not collapsing. Same for intercooler couplings. I like to pressurize the intake and spray soapy water to find leaks.

Verify fuel pressure and look closely at the injectors. They are notorious for leaking from the cap. Look for pooling on the lower intake or follow your nose.....You will smell it. Look and make sure the fuel filter is installed in the correct direction. Not sure if it's possible to install backwards but look that the arrow points to the engine.

If the problem doesn't reveal itself.....Things get a little more involved. How old is the timing belt? You may need to see if it's jumped a tooth. Check compression and look for a bad valve. Make a block off plate/gasket for the EGR to ensure its not leaking (there was a TSB that put a delay valve in the vac line that essentially disabled it anyway). You may need to disconnect the downpipe and go for a ride to see if it's because of a plugged catalytic converter.

I'm sure there's more but that should get you started.

Good luck
John

1988 Turbo Coupe Boost Problems

Reply #5 – March 12, 2017, 10:57:26 AM

Guess I was typing as you posted..lol

1988 Turbo Coupe Boost Problems

Reply #6 – March 12, 2017, 10:58:01 AM

Also, does the car run any different with the VAM unplugged?

1988 Turbo Coupe Boost Problems

Reply #7 – March 12, 2017, 10:59:52 AM

Lol, sounds like we're thinking similar things.

1988 Turbo Coupe Boost Problems

Reply #8 – March 18, 2017, 05:44:28 PM

I was finally able to test the fuel pressure today. I had to order a adapter for my tester. The book says the fuel pressure should be 39lbs. The fuel pressure currently is 30lbs. I tested it with the vacuum line on and off of the pressure regulator. The reading didn't change. It is a steady 30lbs. I increased the engine rpm and it dropped a little. I'm thinking the fuel pump is on the way out. The ECU calls for more fuel and it can't deliver. I don't believe it's a injector problem because the car idles smoothly and is more or less drivable until you put a load on the turbo. The car only recently started acting up. It was doing it before the tune up. I believe the fuel pump is the original. When I first bought the car a couple of years ago it ran like a scolded dog. No problems at all. I think my manual gives instruction on how to test the pump. I'll look into it tomorrow. I appreciate all of the input.

P.S. I will try the things you suggested. I buy only Motorcraft parts if available.

1988 Turbo Coupe Boost Problems

Reply #9 – March 18, 2017, 05:59:14 PM

I always checked fuel pressure under load, if it can't make 54psi at 15psi boost(boost + base 39), the pump and/or the regulator are bad... If it's never had pump replacement it's probably kaput... First TC I owned was dropping pressure under boost before it rolled up 90K...

1988 Turbo Coupe Boost Problems

Reply #10 – March 18, 2017, 06:43:13 PM

Right now it can't make 39psi at idle. Now that I think on it, when I turn the key on the fuel pump does run but it sounds sick, not smooth. I don't know if that's a normal sound. Like I said, I do believe the pump is original. Even if it is a replacement it was most likely done many many years ago. She should be back in top form soon.

1988 Turbo Coupe Boost Problems

Reply #11 – March 18, 2017, 07:02:45 PM

LOL, a groning pump is a unhappy or dieing pump... These same pumps were used in 5.0Stangs and because fuel pressure never had to be more than 39psi often isn't obvious they're on the death bed... If it can't make more than 30psi your pump likely been failing for the last 10K miles...

I bought one that could barely make 25psi and that was deadened, fuel gage connected directly to filter outlet... Yeah it ran very poorly at anything more than idle...

1988 Turbo Coupe Boost Problems

Reply #12 – March 19, 2017, 12:11:15 PM

Quote from: TurboCoupe50;459836

I always checked fuel pressure under load, if it can't make 54psi at 15psi boost(boost + base 39), the pump and/or the regulator are bad... If it's never had pump replacement it's probably kaput... First TC I owned was dropping pressure under boost before it rolled up 90K...

THIS. In a class I recently had, the instructor spent a lot of time stressing that an idle fuel pressure test is worth just about dick. Ideally, you want to attach the gauge and rout it so that it can be seen from the driver's seat with the hood down. You drive the vehicle and look to see if the pressure falls off under load, or increases. If it increases, you're probably not looking at a fuel delivery problem. If it drops, you're underfueling. Change the filter and retest, if no improvement, replace the pump. This measures the pump's ability to provide adequate volume, without adequate volume, good pressure is useless.

1988 Turbo Coupe Boost Problems

Reply #13 – March 24, 2017, 10:53:27 AM

Quote from: TheFoeYouKnow;459852

THIS. In a class I recently had, the instructor spent a lot of time stressing that an idle fuel pressure test is worth just about dick. Ideally, you want to attach the gauge and rout it so that it can be seen from the driver's seat with the hood down. You drive the vehicle and look to see if the pressure falls off under load, or increases. If it increases, you're probably not looking at a fuel delivery problem. If it drops, you're underfueling. Change the filter and retest, if no improvement, replace the pump. This measures the pump's ability to provide adequate volume, without adequate volume, good pressure is useless.

I tested the fuel pressure according to the Ford service manual for my Turbo Coupe. I have no way to test it under load. I replaced the filter less than 2 months ago. From the way the car is acting I'd say it's fuel starved. I plan to drop the tank and remove the fuel pump assembly tomorrow 3/25.

1988 Turbo Coupe Boost Problems

Reply #14 – March 24, 2017, 01:41:24 PM

I'd say it's safe to say that if it won't make the required pressure at idle, it won't make it under load.

It wouldn't be a bad idea to upgrade the pump in case you feel like adding a bit more power down the road.