Acceleration flat spot

[perce111]

Almost every time that I jump on it the car will jump out good, boost comes right up and all is fine until about 3500-4000 when it goes flat, the car still accelerates but it's like a non turbo motor. Gauge still shows about 15lbs. The car was worse prior to installing 86 injectors and a PE ECU. It was a one owner 1985 SVO with 45K miles [I'm #2]. It is also running a full 3" exhaust.
Anybody have an idea?

Thanks

[blueboss]

Timing or fuel pressure.........

[Horsewidower]

That's just about at peak torque. You may be experiencing knock at that point and the ECU will start to pull timing.

My experience is that usually means that your fuel pump is not keeping up, and may be going out.

Plumb in a fuel pressure gauge, tape it to your windshield and go for a ride. You should be able to tell if that is the problem.

[Alex L]

fairly sure that all 85s came with the square intake, but just to be pedantic: square or inline intake?

[NavySVO]

[QUOTE=Alex L;253856]fairly sure that all 85s came with the square intake, [QUOTE]
early 85s had the inline

[Alex L]

early 85s had the inline

knew there was a reason i had doubts about saying 'all 85s'. an ECU programmed for the square intake will not work properly with an inline intake when the knock sensor is plugged in. it will pull timing even without knock being present. not sure if the PE was square only, or if it had 2 code bins for square/inline applications. all of which is moot if the OP is running a square intake

[NavySVO]

knew there was a reason i had doubts about saying 'all 85s'. an ECU programmed for the square intake will not work properly with an inline intake when the knock sensor is plugged in. it will pull timing even without knock being present. not sure if the PE was square only, or if it had 2 code bins for square/inline applications. all of which is moot if the OP is running a square intake

That is where I thought you were headed with this. The PE doesn't react the same as the LA3 in this aspect. It has been stated before that the PE is plug-n-play with the same performance as in an 85.5 and 86

[Alex L]

It has been stated before that the PE is plug-n-play with the same performance as in an 85.5 and 86

even if you go from square to inline? interesting. looser knock sensitivity compared to the L series? not gonna sweat the details on that one. carry on with your normally scheduled troubleshooting thread.

[GAboySVO]

The PE is plug and play as far as the wiring harness, but that does not mean that there is no differences. The boost controller circuit is different and the style of intake will make a difference. They have different acoustic properties so the knock sensor calibration will be different.

If you have an inline intake and a PE ECU, unplug the knock sensor.

[perce111]

Thanks for the input.....
Now I'll go to work and cure the problem

This is the kind of thing that made me want to join the organization.

There is no better input than from the guys that live with them.

Thanks

[jkboyd]

Did you ever determine your problem? I am experiencing a similar problem and am curious what you found. Thanks.

[perce111]

Flat spot

I am currently filling with premium and topping off with octane boost.

I don't think it has solved the problem but it is measureably better.
I haven't checked the turbo for play and I understand that this can cause the same condition.

I need to find a dyno and get on it with some good diagnostic equiment and quit shooting in the dark

I converted to the 1986 PE computer [that helped some] and went with the larger injectors.

maybe I just expect too much

Good luck in your hunt.
If you find the magic component please let me know.

Percy

[jkboyd]

Flat Spot

Percy

My problem sounds very similar to yours. The car boosts and accelerates up to a point, between say 4K or 5K then just goes flat but the boost gauge is still reading boost etc. and the revs continue to increase but very slowly.
The car has been like this since I bought it. I know it's not right because I had a new 86 back in the day and when I got on that car I would easily and routinley bump up against the rev limiter but that is not the case with this car. The first time I drove this car I actually pulled the airbox etc apart to see if a rag had gotten stuck in there. I thought well it's been a long time since you drove an SVO and maybe my butt meter has changed but I don't think so due to the fact that it is difficult to get this thing to run up against the rev limiter.
I have done a ton of things since I got it and nothing really has made a difference up top in the rev range.
The first thing I did was a complete tune up, all Motorcraft, new fuel filter, set timing, set TPS, checked fuel pressure at idle, and read the codes all ok except I had a bad EGR solenoid and that made a slight difference when I fixed it. Everything else was fine.
I've since installed a cone filter, manual boost controller, gotten rid of the flex hose between VAM and turbo, had Evergreen rebuild turbo (found out it has a Grandnational compressor), installed RR cam with new valve springs and seals, installed supercoupe TB installed, 255gpm fuel pump, installed e6 manifold with full three inch downpipe into 2.5 maganflow dual exhaust w/o cat, new clutch and pressure plate, and probably a few more things I forgot. As much as I've freed things up this thing should rev like crazy.
I obviously didn't replace/change all these things trying to fix this problem I just have done a lot and it doesn't run much better on top. Down low it runs great, the turbo spools up quick and this thing actually feels torquey!
I suspect for whatever reason it's running lean. I am going to tape a fuel gauge to my windshield and get a reading under boost. I pulled the vacumn hose off the FPR, which is stock, but didn't see any fuel so I figured it was ok. If there is a problem with fuel pressure at boost I'll investigate the FPR and also on the 86's there is a funky vacumn/boost regulated resistor that regulates voltage to the fuel pump, could be it's not allowing the pump to get full voltage at boost. If I don't find a problem with fuel pressure I'll check the knock sensor.
I'll keep you posted.

Kevin

[jkboyd]

Well I went through and checked for vacuum leaks and found that the fittting for the BPV was leakiing where it screws into the IC so I fixed that and replaced the vacuum line to the FPR (when I went to remove the line it fell apart). Then I ran the gas in the tank down to empty and refilled with fresh gas. The car ran mildly better but what I noticed was when I get on it the boost will spike up to around 19 psi then drop down to about 16 psi (I have a Gillis valve set for around 16 psi). When it spiked I could hear what I thought was very faint pinging so I figured ok the knock sensor is pulling out timing so I added octain booster and the acceleration is much improved.
It still doesn't run quite like I think it should but I think that is due to the ranger roller, that cam just doesn't have anything up top. I've got a boport 1.5 that I am going to install when I get the time, I think it will make a huge difference.
I think my biggest problem is crappy gas, it just deteriorates too quick. I don't drive my car all of the time and it may take me months to use up a tank. I think from now on I won't fill it completely up just put about 10 gallons in it and add fuel stabilzer (I've found that Startron works good in my motorcycles I use to use Stabil but it doesn't work well with the high Ethonal content gasoline) and some octane booster.

[Gyrhead]

I just went through this with my 86 2R. After much diagnosis, it turned out to be both the KS and the vacuum/pressure actuated fuel pump voltage switch. In case you didn't know, there is a vac switch up against the driver's firewall (in 85.5 and 86 cars, IIRC) that feeds full voltage to the FP when the vac signal drops and reverts to pressure on WOT. I peeled back the rubber sock, unplugged the switch and jumpered the pigtail. Instant fix. I took it easy till the KS was replaced tho.