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We have found in our testing and a good rule of thumb to use would be adjusting your fuel pressure to 14psi. The GM manual recommends 9-13psi. The Crossfire motor will "Not" run properly on a fuel pressure setting of 12psi or lower, so the 13psi GM setting is marginal at best. You can adjust to a higher fuel pressure with a stock motor, but we don't recommend it and it won't make a big difference or needed.
Yes, it is "extremely" important on a crossfire motor to know what the fuel pressure is set to in order to get the maximum performance from the motor. A low fuel pressure will make the motor run lean and run out of power especially on top end around 4,000rpm or greater.
3. Will I gain better performance by installing 80lbph or 90lbph injectors on a stock crossfire motor?
No, you will not gain anything by installing either injector on a stock motor. Actually you will be increasing the fuel beyond the motors ability to use it efficiently and the stock ECM can not utilize them correctly.
If you have a rather highly modified 355, 357, 377 or 383 cubic inch motor or higher, you need to install these size injectors and increase the fuel pressure to a minimum of 20 psi to feed the motor properly. It may also be required to run an even higher fuel pressure with these motors depending on the cam selection. Along with the higher injectors and fuel pressure, you will also need to install a different ECM to handle these mods. A modded GM1227747 or GM1228746 ECM are the favored choices along with other mods like the HAM (Harness Adaptor Module), Prominator, EBL (Embedded Lockers) and Ostrich.
This is a very common issue with crossfire motors. The stumbling is probably from a weak fuel pump, low fuel pressure, dirty fuel filter, a dirty fuel pump sock or all the above. We recommend that when replacing any of the fuel system parts to use AC Delco parts only. We also recommend replacing the fuel pump if necessary to the corvette 1985 - 1987 fuel pump which is a direct replacement. Set the fuel pressure to 14psi. The erratic idle both high and low is more than likely caused by a vacuum leak. The main cause of this is the top plate bolts loose on the stock manifold and the throttle body shafts are worn out and leaking. The shafts go bad generally at around 50,000 miles and need to be bushed. See our Services page for more information. Services Page
The fuel pressure regulator is located in the rear throttle body on both the 82 and 84 Corvettes and the 82 and 83 Camaro's and Firebirds. The stock fuel pressure regulator is blocked off from the factory. Remove the rear throttle body tower and the regulator "can" on the bottom of the tower. "CAUTION", there is a considerable amount of tension on the regulator spring when the "can" screws are removed. Now remove the round small anti-adjust plate in the bottom of the regulator "can" that is blocking the hole. After removing the plate, the regulator is now fully adjustable. Now would be a good time to rebuild the throttle body or at least replace the regulator bladder at this time while apart.
The most likely culprit is the CTS (Coolant Temperature Sensor) is bad and should be replaced. It is the sensor that screws into the front of the stock crossfire manifold horizontally and has a small plastic shield around it. Replace the sensor with the newer two pin weather pack type. Do not wrap the threads with Teflon tape if you decide to install the stock type again, the threads/sensor body provides a ground through the block. Also check the O2 sensor if it is happening in closed loop as well.
The easiest way to check your throttle body's for play is to use our 82/84 TB Shaft Wear Test by clicking the following link and viewing the PDF file. You must have Adobe Acrobat to view this file.TB Shaft Wear Test
More than likely it is your O2 (Oxygen) sensor either bad or is cooling off too much causing the ECM issue, the latter usually being the problem. To remedy this from happening, replace your O2 sensor with a heated O2 sensor. You will have to add in a new power source for the heated sensor in the wiring which is simple.
There are a few possibilities for this. Check to ensure that the fuel pump is running and sock is not plugged, replace fuel filter, check the throttle body fuses TB#1 and TB#2 (3A), ensure that the injectors are firing by using either a test light or "noid" light. Also check the fuel pressure is at least 14psi using a fuel pressure gauge. If all these check good, check the ECM connectors, HEI module or HEI reference wire on ECM (conn 452, pin2) to HEI for short or open if less than 1.0 volt.
Yes, after you receive the throttle bodies back from us you must reestablish the throttle body balance and reset the TPS sensor back to .525volts and set the idle. After accomplishing these tasks, the motor should perform well again and idle smoothly.
12. My motor starts for a short time and then no fuel sprays out of either injector, if I pour gas down the throttle body it will briefly run, what is wrong?
There may be several issues causing that condition. Here is a list of probable causes, evaluate each one before proceeding to the next. Injectors not firing, fuel pump, fuel pump sock dirty, fuel filter dirty, dirty injectors, fuel pressure too low (set to 15psi) or fuel pump relay.
This is a tricky and somewhat controversial question to answer. Yes, you will see better performance gains over the stock heads by going to an aftermarket head, the stock heads do not breathe well. However, bigger isn't always better when dealing with a wet system crossfire motor. The key on head choice is two fold, one that the head flows better than stock and two, the velocity needs to remain high. To retain the higher velocity, you must select a head with a smaller runner. A 170cc runner works well on a stock motor while a 180 to 195cc runner works better on a highly modified 355 on up to 383 cubic inch motor. Our preference lays with the 180cc runner head being the middle ground best choice. Remember, if you lose the velocity and the fuel drops out of suspension, you loose any performance gain by going to an aftermarket head. It is also a good idea if you're going to replace the heads to port the intake manifold or purchase a Renegade manifold to optimize your gains even further.
Check to ensure that the injector itself is working ok by swapping them or swap the connectors and see if issue moves to the other injector. If that doesn't work, there are two fuses that power the injectors in the fuse box, INJt#1 and INJ#2, both of which are 3amp. If this is not the problem then check the wiring from the injectors to the ECM and the ECM connector for a good connection to the ECM edge card. If that is ok, then the Injector driver circuit may be bad in the ECM.
This question is somewhat hard to answer and has no absolute values because of various reasons dealing with engine condition, proper maintenance, total miles and modifications that have been done. Gains will vary, but generally, through our testing we have seen a 30HP gain to the rear wheels and more over a stock crossfire manifold and throttle bodies that are set up properly. We have also seen a 20HP gain to the rear wheels over other crossfire adapted type manifolds on larger displacement engines.
16. I heard that installing two inch throttle bodies or larger will increase the performance of my stock crossfire, is that true?
We do not recommend installing two inch or larger throttle bodies or increasing the injector sizes on any stock crossfire engine. Increasing the fuel pressure to 13-14psi to your stock crossfire injectors will usually show a marked improvement in performance along with a good balance. A word of caution; It is always a good idea to do a rebuild on any throttle body that is old or an unknown condition before increasing the fuel pressure to be on the safe side. The bladder inside can become very weak over time and may blow out with the added pressure.
Another tough question to answer and no real specific answer as it depends on a lot of variables on both of these engines. Generally, a two inch throttle body using either an 80lbph or 90lbphr injector will work fine even on a 383 motor. Just like head selection, on a crossfire doesn’t mean, “Bigger” is always better. Another item to consider is that you may/will need to change your stock ECM to either a GM1227747 or GM1228746 which is the typical choice and have it modified to accommodate for laptop tuning. We recommend utilizing the EBL and Ostrich setup with our HAM board mod. There are other ECM units to choose from as well.
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Would you like to have your Corvette, Camaro or Firebird featured on our site? As a DCS customer, all you have to do is send us a 400x300 pixel jpg file and we'll post it in the Gallery section. Also tell us a little about the mods you have done for others to see.