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Running lean under boost!

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92tsifwd

15+ Year Contributor
572
0
Feb 1, 2004
Hastings, Nebraska
Ok I finally got my wide band calibrated and installed. I have been fighting a lean issue with my 90 Talon awd since I bought it a year ago. I bought it with a bad ecu and it was running lean closing the gaps and showing signs of detonation on the plugs. I went to BPR8ES plugs put in an eprom ecu that was rebuilt by ecm tunning and tested. I have swapped coil pack, transistor, It now has Delphi 1000cc injectors and aromotive A -6 regulator at 43.5psi, -6 from filter to rail, walbro 255 lph hp rewired, getting 18 volts at pump at idle. eprom set for injectors and 2g maf. Car runs about 14.5 afr when cruising and around 15.5.1 at idle which might be a tad lean. When under wot it is around 12.0.1-12.5.1 afr. If I stay in it it will break up and close the gap on # 1 spark plug. I have now confirmed it is a lean issue. What would cause this? The tune is very conservative with 16* total timing and 11.0.1 set in the eprom. There are no boost leaks what so ever. tps is set with logger to 10.1% closed throttle. I will check it with a volt meter. The base timming is at 5* btdc. It is not 180* off. Would a cas cause this or a injector resister pack? There is a a/f gauge tapped into the stock narrowband. Would this cause a voltage drop? I am using a NGK afx wideband in the downpipe right under the firewall. The car goes lean as soon as I get into boost.
 
I checked the tps with a digital volt meter and .83 at closed throttle test and 8.23 volts at wot. no spikes or jumps. getting 8.23 volts to power wire and ground checks out. tried a spare maf from my perfectly good running 2g eclipse and no change.

I believe the injectors are scaled right as I have had this problem long before with the stock injectors and the car runs great exept when under boost. 1st gear I hit 11.7.1 2nd 12.2.1 and 3rd 12.2.1-12.5.1 and I let off as that is real lean. The more load the leaner it gets. This is at 12lbs lowest boost . Fuel press is 43.5psi with vacume line off. batt is seeing 19 volts when running. pump is getting 18 volts.
 
Get the alternator checked, that voltage is way too high. You should never see more than 15 volts in the system. The sensors should only be getting about 5 volts, not 8.

Might want to inspect the FPR as well.

Will do today. I don't remember getting that high of volts when I first bought it so must have happened recently. I will check for the 1psi rise ratio today also.
 
Turns out my volt meter took a crap. Borrowed a buddies and 12.9 volts with engine off and key on at batt. tps is toast. it shows .51 volts closed and is fine until I hit about 30% throttle and then it hits a dead spot and load value goes to almost nothing even though the voltage will come back at around 85% or so the load is still low. then when you go down same thing dead spot until you get down to like 30% throttle. I am getting 4.99 volts to power and ground is good. This explains why it ran great at low throttle under 30%. Looks like I found the problem. Now to find a tps for a 90. Parts store wants $175 plus freight.
 
Ok I set the tps to .51 volts at closed throttle and I am getting 4.88 volts at wot. Is this correct? It is still going lean. The leanest it hits is 12.0.1 and is mostly around 11.5.11.7 range. It has not fouled the plugs yet like it usually does. On the last 1st gear pull the exhaust changed tone and broke up until I let off, so not sure if that was timing retard, and it runs like crap for a minute after this and then it is back to running normal. I might try dialing in the injectors slightly smaller to see if that helps. Also checked the aromotive reg for the 1psi rise rate and it increases fuel press exactly 1psi fuel press per pound of boost. I went 17 psi and it was at 60psi fuel pressure. I am out of ideas other than going to try adjusting injector size to slightly smaller.



I got the injectors set now and I am getting 10.98-11.0.1 a/f now at wot. I am still getting the cut out issue at 5-5500 rpms though and as soon as it does it the exhaust tone changes and it goes lean and it closed the # 1 spark plug gap today and partialy closed # 2. When it does this afterwords the car will spudder and miss for about a minute and then return to normal if the gaps are not closed. It does not always close the gaps. Also I am getting random misfire during part throttle driving now. The only thing I can think of is the cas or camshaft position sencor is going. This is the only thing I have not swaped out or tested. Can a 91 cas be used on a 90?
 
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Can someone comfirm that a bad CAS would inditcate this type of symptom? I unplugged me CTS and it made zero difference to how the car runs, I';m guessing it could have a short. This car is going to a mechanic.:banghead::banghead::banghead:
 
I replaced the cas and converted from the 90 to the 91 and made my own wire plug adapter. It still has not solved the problem. I also verified I have 13.75 volts to the pump at idle and I ran a new ground straight to the the fuel pump cover. No change. It still does it. I only have the injector resistor pack left to test and the wiring harness possibly fuel pump relay. I am going to mount a fuel pressure gauge inside the car so I can verfy its not a fuel pressure drop off problem.
 
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