North American Turbocoupe Organization



Detonation and Adjustable FPR (Long Post)
Rockhead Offline
Junior Member
#1
I am having a very small detonation problem (if you call ANY detonatation "small") and could use some guidance. Here is the story.

1988 TC 5 speed with 62K miles...original owner. Motor is stock except for a K&N cone filter and a 180* thermostat. Car has never given a hint of any problems, detonation, etc. A recent tuneup of Motorcraft parts (e.g., plugs [gapped], cap, rotor, wires, timing belt, timing belt tensioner, fuel filter)was completed. Compression test shows all cylinders between 142 and 160 psi on a cold motor (no. 4 was the lowest, no 1. was the highest). Vacuum at idle is a steady 19.5 inches Hg and vacuum spikes to 22-23 inches when the throttle is snapped closed from 2,000 + rpms. No codes whatsoever....11 all the way around. Timing set at 10* BTDC with spout out and car runs fine just like it always had. Car always showed 15 psi boost on the stock guage. No detonation whatsoever.


I ran the car for about one week after the tuneup with no detonation and then installed a Gillis Valve. Boost was set to 15 psi with an accurate aftermarket guage (which just happened to agree with the stock boost guage...so overall boost level didnt change much if any). Now I am getting a very minor amount of detonation only at WOT at rpms between 3,000 to 4,000. I don't here it above 4,000 rpm if its present. The detonation is so slight and is NOT always audible.

Thinking it was the fuel, I tried dry gas, changed fuels, fuel system cleaner, etc., but the detonation is still present.

Ran the fuel system test after Pete so kindly emailed me the procedure (thanks again Pete). Fuel system test results were as follows:

a. KOEO FPR vacuum line connected showed 40 psi with pump running. As soon as the pump is turned off, the guage drops to 38 psi and then will hold 38 psi for an excess of 5 minutes.

b. KOER FPR vacuum line connected 30 psi.

c. KOER FPR vacuum line NOT connected 40 psi.

e. Driving conditions under full boost shows 55-56 psi.

d. Fuel pump pressure immediately after fuel filter 98 psi.

e. Fuel pump delivery rate immediately after fuel filter between 85-90 ounces of fuel per minute (no restriction so pressure is minimal).

Based on the above, everything appears to be in order, but I would like to increase boost to 16 -16.5 psi with a bit more timing, say 12* BTDC, without detonation.

Now my questions.....

1. While the detonation could be a result of almost anything, I really don't feel like chasing down the smallest of possible gremlins if installing a Kirban adjustable FPR would likely solve my detontation problems. What do you think? Would installing an adjustable FPR give me the fuel to cure the detonation with the increased boost and timing?

2. Would the Kirban model no. KIR5005 (fits '86 to '93 Mustangs) be a direct replacement for the stock FPR without modification? Here is the link to the part......

[link]http://www.jdsperformance.com/index.asp?initemuid=147&fcmd=item&inmake=all [/link] (crap, sorry, dont know how to post a link)

3. If the Kirban it is not a direct replacement for the stock unit, where/how do you mount the Kirban FPR?

Thanks for reading the post and thanks in advance for any assitance/recommendations.

[This message has been edited by Rockhead (edited 08-31-2003).]

[This message has been edited by Rockhead (edited 08-31-2003).]

[This message has been edited by Rockhead (edited 08-31-2003).]
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Pete D Offline
Administrator
#2
Your fuel pressure is fine, especially while driving in boost.

Are you absolutely sure its detonation and is your KS still connected?

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NATO Member. it's not a vice, it's an obsession
Letting the cat out of the bag is a whole lot easier than putting it back in.
88 TC X 2, 86 SVO, mods list at
http://www.turbotbird.com/showroom/pd_88tc.htm
Pete Dunham


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Noname
Guest
#3
Rather than take it for granted: are you running premium gas?
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Rockhead Offline
Junior Member
#4
I am sure its detonation, but like I said it is quite minimal. I came to the detonation conclusion because if the timing is advanced a bit, say to 12* to 13* BTDC, the detonation is more audible. Same holds true if I increase the boost a bit. When I back the timing off to 10* and turn down the boost to 15 psi, the detonation is minimal.

Knock sensor is connected and premium gas has always been used.

The spark plugs which we replaced during the tuneup were fine.

I'll add an "inquiring minds" question to my original post.....if one does install an adjustable FPR and sets the base fuel pressure to say 3 psi higher than the stock FPR reading, what assures that the fuel pressure under maximum boost will actually be higher than the stock fuel pressure level under maxiumum boost? Since the FPR is influenced by engine vacuum as well as the spring and diaphragm internal to the FPR, what happens if the adjustable FPR has a different rate spring than the stock FPR?
Maybe I just dont understand the complete working details of an FPR.
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Glenn 88TC Offline
Posting Freak
#5
If the knock sensor is connected you shouldn't hear any detonation even if the engine starts to. It is supposed to retard the timing and take the detonation away.

The aftermarket fuel reg. works the same as the stocker. It uses maifold pressure to raise the FP 1psi per psi of boost. So if you set it to 43 psi and run 15 psi of boost it should read a total of 58psi. The Kirban you mentioned is the one I use and it is a direct bolt on.

What makes it even more unusual that you are experiencing pinging(even with the KS connected) is that the eec goes way too rich in the rpms you mentioned. The eec will cause tthe car to go very rich at the on set of boost and then gradually lean the car out. Has your gas mileage suffered or is the ex. manifold glowing red at all. Maybe the O2 sensor is heading south and causing the car to run leaner than normal. I've had them go bad and never show a code.

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mods: SDS Digital Fuel Injection, ported & polished big valve head(1.89/1.59), .500 lift roller cam, custom upper and ported lower intakes, TE60 turbo, powerstroke intercooler, 60mm throttle body, 75pph injectors, Walboro 255HP pump, Kirban adj. fuel reg., ATR header, 3" exhaust with Dynomax Ultraflow muffler, MSD 6al, MSD coil, MSD Launch Control, MSD 8.5mm wires, K&N filter, Star stage III clutch, Greddy Profec B boost controller, Weld Draglites with M/T ET Street 26x11.5/15
NO TC and NO headaches.
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Pete D Offline
Administrator
#6
Maybe I missed, but if you havne't done so, pull the codes.

------------------
NATO Member. it's not a vice, it's an obsession
Letting the cat out of the bag is a whole lot easier than putting it back in.
88 TC X 2, 86 SVO, mods list at
http://www.turbotbird.com/showroom/pd_88tc.htm
Pete Dunham


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Jeff K Offline
Administrator
#7
I agree that if the KS is connected, you will never hear the detonation, as the KS is much more sensitive than human ears to detonation. It is possible, but not likely that the KS has gone bad, but a KS hardly ever fails. Did you run the KOER test, and tap on the intake with a wrench at the dynamic response code to exercize the KS? If you dont do this, you should get a KOER code 25 every time you run the test.

If you actually have detonation now with the Gillis valve you didnt have before, I can only think of one possibility: With the stock BCS system, the EEC doesnt allow 15 psi until over about 4000 to 4500 RPM, so if you get 15 psi, say, at 3000 RPM, the EEC may not be adding enough fuel, since it thinks boost will only be 10 psi. I know the VAF should somewhat take care of this, but who knows? What I would do is add about 2 psi more base fuel pressure and see what happens. THe EEC will compensate for this when in closed loop, and it will only run a little righer under open loop (i.e., WOT). Every engine seems to be different, some will run fine with stock fuel pressure at higher than stock boost, some need more fuel pressure.

One more note: you really need to measure fuel pressure under WOT / high RPM / high boost to see if it is base press plus boost press. A weak fuel pump / clogged filter can supply pleanty of volume / pressure at idle, but not at high boost / RPM where fuel demand is greatest.

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 02 Taurus Vulcan(wifes car)
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.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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Rockhead Offline
Junior Member
#8
Glenn.....

Exhaust manifold does not glow...have been checking that every so often as of late.

Also have not noticed any significant decrease in gas mileage, but honestly, since the car is only used for around town and some spirited driving, I havent actually kept track of the mileage. Let's just say it "seems" about the same as it always had. If the mileage went down, such would indicate a rich condition and I would think less chance of detonation.

Maybe the O2 sensor is indeed going bad. Codes say nothing. I guess I will have to do a search and check for the 02 testing procedure. I would hate to replace the sensor and find it is still good.

Pete.....

No codes show...all 11.
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Rockhead Offline
Junior Member
#9
Quote:Originally posted by Jeff K:
If you actually have detonation now with the Gillis valve you didnt have before, I can only think of one possibility: With the stock BCS system, the EEC doesnt allow 15 psi until over about 4000 to 4500 RPM, so if you get 15 psi, say, at 3000 RPM, the EEC may not be adding enough fuel, since it thinks boost will only be 10 psi. I know the VAF should somewhat take care of this, but who knows? What I would do is add about 2 psi more base fuel pressure and see what happens. THe EEC will compensate for this when in closed loop, and it will only run a little righer under open loop (i.e., WOT). Every engine seems to be different, some will run fine with stock fuel pressure at higher than stock boost, some need more fuel pressure.

Jeff...

Your comment above is exactly what I was thinking and your solution is what I intend to try to rectify the problem. Without knowing exactly how the EEC is programmed, it is quite possible that seeing an additional 5-6 psi at 3,000 to 4,000 rpms is outside the normal programmed "range" for the EEC and it simply cannot compensate enough.

Fuel pressure at idle was 40 psi and fuel pressure was 55-56 psi at WOT in 4th gear.

One interesting thing happened today....I checked codes again today...nothing on the KOEO. But when I went to do the KOER test (I had not run this test before), shortly after the engine did its wild thing just after the start of the test...the engine died. It did this twice. I could not get the KOER test to complete...the engine died each time shortly after the start of the test. Any ideas.
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Pete D Offline
Administrator
#10
I've had it die once or twice and I ususally give just enough throttle to keep it running. Don't know if it allowable or not but I got codes out of it.

------------------
NATO Member. it's not a vice, it's an obsession
Letting the cat out of the bag is a whole lot easier than putting it back in.
88 TC X 2, 86 SVO, mods list at
http://www.turbotbird.com/showroom/pd_88tc.htm
Pete Dunham


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