Engine '88 GT Has No Power Above 3000 RPM After Trick Flow 11r Heads Install

John Dirks Jr

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Jun 28, 2013
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One thing I also noticed about your parts list. You say the car has been converted to mass air. That’s good. However, your parts list says you replaced the MAP sensor.

Now, a MAP sensor would be an essential component on a speed density setup like normally would be on an 88 car and has a vacuum line connected to it along with some wires. A mass air car does not use a MAP. instead, it uses a BAP. The MAP and BAP look almost identical and would be mounted in the same location from factory. In the speed density cars, the MAP measures manifold pressure/vacuum. In a mass air car, the BAP measures atmospheric pressure. A BAP would have wires connected to it, but it would not have a vacuum line.

So, does this component you have listed as the MAP have a vacuum line connected to it? Because in a mass air Foxbody, it should not.

I’m thinking maybe there’s a mismatch of system components
 
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JRerecich

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One thing I also noticed about your parts list. You say the car has been converted to mass air. That’s good. However, your parts list says you replaced the MAP sensor.

Now, a MAP sensor would be an essential component on a speed density setup like normally would be on an 88 car and has a vacuum line connected to it along with some wires. A mass air car does not use a MAP. instead, it uses a BAP. The MAP and BAP look almost identical and would be mounted in the same location from factory. In the speed density cars, the MAP measures manifold pressure/vacuum. In a mass air car, the BAP measures atmospheric pressure. A BAP would have wires connected to it, but it would not have a vacuum line.

So, does this component you have listed as the MAP have a vacuum line connected to it? Because in a mass air Foxbody, it should not.

I’m thinking maybe there’s a mismatch of system components
Interesting. Any significant way to tell the difference between a MAP and a BAP just by looking at them? Maybe I’ll go to the local parts store and see if they have the BAP listed as a different part.
 

John Dirks Jr

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The correct part for a MAF car is BAP. It has no vacuum line. It does have a grey cylindrical cap on the port. Looks like this.

9F6707B4-B7BD-4F36-AB4E-81AC6D7EDEE8.jpeg
 

John Dirks Jr

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Jun 28, 2013
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Are they the same sensor? Just ones connected to vacuum and ones not?

I dont know about the actual difference between the two or if there even is a difference. Important part is that in your case, you say there is no vacuum line connected.

Now go back to post #20 where I asked some questions. Those are important questions.
 

JRerecich

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We just swapped spark plug wires with the stock ones as number 4 wire touched the headers and burnt through, causing arcing. Sounds better, but basically once I get to around 3k it starts to sputter and sounds like misfire. Then, as soon as it hits 4,500 rpms it stops there, will not go past. Similar to the rev limiter. I wish I had more information from the dyno, but we didn’t get any dyno sheets or exact data.
 

John Dirks Jr

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Check the fuel return lines that are down below the #1 spark plug at the right front side of the engine. The stock ones transition from steel to plastic and back to steel as they go down from the top of the engine and back along the frame. The plastic portion allows for movement as the engine vibrates and moves from torquing in the mounts.

if these lines are out of position they can get kinked. A front end alignment mechanic pushed my lines out of his way when he was working on the alignment. It kinked the plastic portion of the line and caused the symptoms like you describe. After I moved the lines back to the correct position and relieved the blockage caused by the kink, the symptoms went away.
 
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JRerecich

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Check the fuel return lines that are down below the #1 spark plug at the right front side of the engine. The stock ones transition from steel to plastic and back to steel as they go down from the top of the engine and back along the frame. The plastic portion allows for movement as the engine vibrates and moves from torquing in the mounts.

if these lines are out of position they can get kinked. A front end alignment mechanic pushed my lines out of his way when he was working on the alignment. It kinked the plastic portion of the line and caused the symptoms like you describe. After I moved the lines back to the correct position and relieved the blockage caused by the kink, the symptoms went away.
I think we are on to something here. I just got done checking fuel pressure and we have 40 psi with vacuum line off and plugged, then 35 psi with vac line on. With the vac line on I started revving it up and it would immediately drop to around 29-30 psi. I didn't check it under load as the gauge was too short. I will be checking all the lines tomorrow for kinks and if everything checks out, I'll plan on putting a high flow fuel pump in.
 

General karthief

wonder how much it would cost to ship you a pair
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I didn't go back to see what you are working with but unless it's a race car just stick with a 155 or 190 pump, sometimes it's just a split hose at the pump or a loose clamp.
Bigger, more is not always better, faster.
 

JRerecich

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I didn't go back to see what you are working with but unless it's a race car just stick with a 155 or 190 pump, sometimes it's just a split hose at the pump or a loose clamp.
Bigger, more is not always better, faster.
255 isn't too much, even when we will be going to a 347 pretty soon? Should the stock fpr suffice?
 

John Dirks Jr

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Whether you find the a kinked line or not I would also recommend checking the hose that connects the fuel pump to the sending unit inside of the tank. It’s common for them to rupture with age. Mine did and here’s what it looked like. It caused my fuel pressure to be low and surge.



C3657CB3-C724-431E-8E24-005BFEA15396.jpeg
 

99Blackbeauty

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Hey bud here just a thought. I have a 99 v6 and was coming home with my wife from town when we hit a hill and my car fell on its face. I had to put it in 3rd gear just to clear the top of the hill doing 45 mph, (a hill anyother day could be topped easily in 5th at 100). From that point on my care responded with the same symtoms as yours. Would not rev. More than 3500 with out losing power. After changing a ton of part my dad and I checked the exhaust. My cats were almost completely plugged. Ended up getting a whole new system from headers back, now my car has a great sound and runs like a champ. If you have not tested your exhaust pressure i would say to try that. Mine were so plugged i could touch my rear pipe after the car had been idling for 15-20 mins. Keep in mind my car ran perfect before i hit the hill and then ran like it was only using half the motor. Very low on power and producted identical symtoms you stated for your post. Hope this helps man. I replaced around 1200 bucks in parts before i found the culprit. But least all the performance parts of my motor are new and i converted from a single to a dual exhaust. Have a great day.
 

JRerecich

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Feb 12, 2020
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Hey bud here just a thought. I have a 99 v6 and was coming home with my wife from town when we hit a hill and my car fell on its face. I had to put it in 3rd gear just to clear the top of the hill doing 45 mph, (a hill anyother day could be topped easily in 5th at 100). From that point on my care responded with the same symtoms as yours. Would not rev. More than 3500 with out losing power. After changing a ton of part my dad and I checked the exhaust. My cats were almost completely plugged. Ended up getting a whole new system from headers back, now my car has a great sound and runs like a champ. If you have not tested your exhaust pressure i would say to try that. Mine were so plugged i could touch my rear pipe after the car had been idling for 15-20 mins. Keep in mind my car ran perfect before i hit the hill and then ran like it was only using half the motor. Very low on power and producted identical symtoms you stated for your post. Hope this helps man. I replaced around 1200 bucks in parts before i found the culprit. But least all the performance parts of my motor are new and i converted from a single to a dual exhaust. Have a great day.
I appreciate the insight, but we put in new long tube headers and the cats have been deleted for a while. I’m positive it’s fuel pressure related after testing it, we just have to figure out where the low pressure is coming from.
 

JRerecich

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Feb 12, 2020
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Kind of at a stand still now. We just replaced the FPR and Fuel Filter to try and fix the fuel pressure issue as we did not find any of the lines to be kinked or torn. There is a tiny screw at the top of the FRP that we were able to screw in and out to adjust the fuel pressure, but that did not seem to help either. I'm going to order a 190 lph fuel pump as a last resort, but at this point we're out of ideas. I linked two videos to show what is happening with the fuel pressure and at WOT.

Pull at WOT - View: https://www.youtube.com/watch?v=1rVZGYcKATU

Fuel Pressure Test - View: https://www.youtube.com/watch?v=4btsm8hD6bo