Welcome to the new FAQ section of XFire Performance. Answers presented here are based on many years of crossfire experience and the assumption that your 1982 through 1984 Crossfire engine is in good running condition, and there are no major mechanical issues or Check Engine Light (CEL) that is on. These questions are some of the most commonly asked questions about the stock Crossfire and modified engines that we get emails on or calls about on a daily basis. If you have questions that are not listed here, please feel free to send us your specific inquiries via the Contact Form on the Contact page. Due to the high volume of emails and calls, we are unable to troubleshoot your specific issues, that’s what the GM service manual is for. If you do not know how to balance your throttle bodies, have a look at #22 below and watch the two part videos on that subject. We highly recommend that you always refer to your GM Service Manual as your final guide on troubleshooting anything or maintenance. If you do not have a GM service manual, please get one. They are worth their weight in gold in troubleshooting any crossfire car. You can also purchase them from us in digital format on our Shop page. I hope you find these FAQs helpful.
Q: What fuel pressure should I use on a stock crossfire motor?
A: We have found in our testing and as a good rule of thumb to use a fuel pressure setting of 13psi. The GM service manual recommends 9-13psi as the range. The Crossfire motor will not run properly (or to its full potential) on a fuel pressure setting of 11psi or lower, so the 13psi GM recommended setting is 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 and probably not needed even if your fuel pump can provide that much flow reliably under WOT. A WORD OF CAUTION We also recommend that you rebuild your throttle bodies if you don't know when the last time this was done. The diaphragm/bladders in both throttle bodies become weak over time and an increase in fuel pressure may be enough to burst them. If that happens, you stand a good chance of catching your car on fire because of fuel pouring over a hot engine.
Q: Is it necessary to know what the fuel pressure is set to on a crossfire motor?
A: Yes, most definitely. The crossfire engine is rather fuel pressure sensitive. 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 engine. A low fuel pressure will make the motor run lean especially at WOT and run out of power on the top end around 4,000rpm or greater. We can help you with adjusting the fuel pressure with our fuel pressure adjustment tool on our Shop page.
Q: My car stumbles and runs rough with an erratic idle, what is wrong?
A: This is a very common issue with crossfire engines. The stumbling is probably from a weak fuel pump, low fuel pressure, dirty fuel filter, a dirty fuel pump sock, out of balance TB issue 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 and has a little bit more flow (gph/lph). Set the fuel pressure to 13psi. The erratic idle both high and low is more than likely caused by a vacuum leak. The typical cause of this is the top plate bolts are loose on the stock manifold and or the throttle body base gaskets are loose and leaking. If you just tighten loose top plate bolts and the gasket is original or very old, it is probably brittle. Also, you will probably crack the gasket further and cause even more leaks. There could be other vacuum leaks and further troubleshooting may become necessary. Always refer to the GM service manual for guidance.
Q: My fuel pressure regulator is blocked on the bottom, how do I adjust the fuel pressure?
A: The fuel pressure regulator located in the rear throttle body on both the 82 and 84 Corvettes and the 82 and 83 Camaro, Firebird and Trans Am engines. The stock fuel pressure regulator was blocked off by GM at 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 four screws holding the "CAN" to base are removed. It is better to use a small clamp to hold it together when unscrewing the screws holding it together so you don't strip them. Now remove the round small anti-adjust plate in the bottom of the regulator "CAN" that is blocking the hole, just punch it out. After removing the plate, the regulator is now fully externally adjustable. Now would be a good time to rebuild the throttle body or at least replace the regulator bladder at this time while apart. You can adjust your fuel pressure easily using out fuel pressure tool available on our Shop page. As always, use the GM service manual as your guide.
Q: I have no fuel spraying from either injector, what may be wrong?
A: There are a few possibilities for this. Check to ensure that the fuel pump is running and in-tank sock filter is not plugged, replace frame rail fuel filter on passenger side, 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 13psi using a fuel pressure gauge. If all these check good, check the ECM connectors and see if the CEL light comes on during key ON briefly, If not, check the 20amp fuse in the battery box. This fuse supply’s the ECM with power. If bad, the engine will crank, you will get spark, but no fuel since the ECM controls the fuel relay and will not power the pump. Also check the HEI module or HEI reference wire on ECM (connector 452, pin2) to HEI for short or open if less than 1.0 volt. The issue could also be the be the HEI pickup coil is bad. Refer to the GM service manual for further guidance if needed.
Q: 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?
A: There may be several issues causing this 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 it to 13psi) or fuel pump relay. Also, it could be the short rubber hose on the fuel tank on top where it connects to the fuel line to the pump/sender assembly; it may be cracked due to age.
Q: I only have fuel coming from one injector, what could be causing this?
A: First, check the two fuses that power the injectors in the fuse box, INJ#1 and INJ#2, both of which are 3amp. Next, 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 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. If you have a CEL light, refer to the GM service manual for more troubleshooting guidance.
Q: Why does my motor bounce between open and closed loop with a 1227747 or 1228746 ECM with headers?
A: More than likely it is your narrow band (NB) 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 and always connect it to a switch source so that it only comes ON when the engine is running so you don't drain your battery. There are also companies out there that make a non-heated stock O2 sensor harness conversion to a heated 02 sensor.
Q: My engine idles rough and rich when cold, what is the problem?
A: The most likely culprit, but not limited to this is the Coolant Temperature Sensor (CTS) 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 on a stock engine and same position on the Renegade manifold. 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 manifold and the block to frame. Use Permatex high performance thread seal sparingly instead. Also check the O2 sensor if it is happening in closed loop as well.
Q: Will I gain better performance by installing 80lbph or 90lbph injectors on a stock crossfire engine?
A: The short answer is No, you will not gain anything by installing either injector on a stock engine. Actually, you will be increasing the fuel beyond the motors ability to use it efficiently and the stock ECM can not utilize them correctly or efficiently.
Q: When would it be necessary to install 80lbph or 90lbph injectors?
A: If you have a rather highly modified 355, 357, 377 or 383 cubic inch motor or larger, you need to install these size injectors and increase the fuel pressure to a minimum of 22 psi to feed the motor properly and go up from there if needed. It may also be required to run an even higher fuel pressure with these motors depending on the cam selection. This cannot be done with a stock crossfire fuel pressure regulator safely. Along with the larger injectors and higher fuel pressure, you will also need to install a different ECM to handle these mods. A modified GM1227747 or GM1228746 ECM are the favored choices along with other mods like the Harness Adapter Module (HAM) board that we sell along with the EBL FLASH II from Dynamic EFI also linked from our HAM board page on the Shop page.
Q: Will I see large performance gains by replacing my stock heads?
A: This is a bit of a tricky and somewhat controversial question to answer depending on the size and chamber used. Yes, you will see better performance gains over the stock heads by going to an aftermarket head, the stock heads do not breathe as well as the aftermarket aluminum heads. However, bigger isn't always better when dealing with a wet system like the crossfire engine. 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 keep the fuel in suspension. When the fuel drops out of suspension your power will suffer.
To retain the higher velocity, you must select a head with a smaller runner. A 170cc or 175cc runner works well on a stock engine. I have used a 180cc Dart Pro1 head on a 357 cubic inch engine and a 383, which later I opted for a AFR 195cc runner works better on a highly modified 383 cubic inch engine which I now have.
My preference rests with the 180cc runner head being the middle ground best choice for a 355 engine and 170-175cc runner for a stock engine and 195-200cc runner for a 383 or higher. Remember, if you lose the velocity and the fuel drops out of suspension, you lose any performance gains by going to an aftermarket head in the first place. It may also benefit you if you're going to replace the heads to port the intake manifold or purchase a Renegade manifold which already has the larger cross-sectional area and 20% more volume to optimize your gains even further. Do your research on this subject before opening your wallet and wasting money.
Q: How can I tell if my throttle body shafts are worn?
A: The easiest way to check your throttle bodies for excessive play is to grab your throttle body linkage and see if you can move it up/down? If you can move it, it’s bad. Sometimes it will rattle if badly worn and WILL NOT hold a balance even if you balance them perfectly, as soon as you press on the accelerator pedal, they will become out of balance and idle. Since you will not be able to balance them properly, the idle quality will suffer. There "will be" play or movement in the horizontal plane in/out which is normal. We may provide a throttle body restoration and boring service down the road, but that is yet to be seen.
Q: I heard that installing two inch throttle bodies or larger will increase the performance of my stock crossfire, is that true?
A: 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 balancing your throttle bodies. 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/diaphragm inside the throttle bodies can become weak over time and may blow out with the added pressure and present an instant safety issue and possible fire hazard.
Q: What size throttle body should I run on my highly modified 355 or 383 engines?
A: Another tough and tricky question to answer and no real specific answer as it depends on a lot of variables on both of these engines. Generally speaking, 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, it doesn’t necessarily mean, “Bigger” is always better, depends on other modifications done. However, with that said, there are guys out there running 2.25" throttle bodies with a 383 engine and running just fine. The Renegade manifold will except up to 2.25” throttle bodies as well. I personally run 2.13" throttle bodies on my 383 with 90pph injectors at 30psi externally regulated. We also now do throttle body boring up to 2.15” which will work great with any highly modded 350 or big cubic inch motor.
Another item to consider is that you may/will need to change your stock ECM to either a GM 1227747 or GM 1228746 which is the typical choice and have it modified to accommodate for laptop tuning. We highly recommend utilizing the EBL FLASH II setup from Dynamic EFI with our HAM board. There are other ECM units to choose from as well.
Q: What kind of performance gains can I expect to see if I were to install the Renegade performance manifold?
A: This is a tough question and 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 and other modifications etc... Gains will vary, but generally, through our testing in a controlled environment on a chassis dyno we have seen on average a 30HP gain to the rear wheels and some even a little more over a stock crossfire manifold and throttle bodies that are set up properly. We have also seen a 25HP plus gain to the rear wheels over other previous crossfire adapted type manifolds like the old XRam manifold on larger displacement engines. The Renegade manifold dropped one person’s 383 engine 1/4 mile ET by over three tenths of a second over the previously installed XRam manifold and he is now running 12.20s naturally aspirated in his 1984 crossfire.
Q: Can I install a large lift and higher duration cam in my stock crossfire engine and still use the stock crossfire ECM?
A: In short, No. The lift is not really the issue, but the higher duration is the problem. You can not stray too far from the stock duration if you decide to keep and run the stock ECM. You must stay around the 210-214(ish) duration @ .050” for the ECM to be happy. The cam can not be a “thumper cam” that likes to lope which will force the MAP sensor to bounce around excessively and in-turn cause the ECM to wig out and not know what to do and set CEL lights none stop. Also, try and keep the LSA closer to 114 if possible which is more ECM friendly.
Q: Can you send me your tune from your 82 CFI?
A: I have been asked this a lot. The short answer is No. I have spent a great deal of money over the years developing my tune for my 383 engine on a dyno. At times, I thought my car was becoming a dyno queen. The price I would have to charge for my tune would NOT be cost effective to anyone and unless your engine was EXACTLY the same as mine, it still wouldn’t be correct for your engine. Sorry everyone.
Q: My orange Check Engine Light comes on, but then goes off. My car runs bad when it is ON, what’s going on?
A: Well, this is another hard question to answer and be specific. There are a number of things that could be causing your CEL to come and then go off. You must read the codes that are stored in your ECM to figure out what is causing the ECM to set your CEL. The ALDL test port is located under the ash tray and you can short pins A/B together and watch the CEL flash. The flashes correspond to the number of the code set. Short flashes followed by long flashes. Refer to the GM service manual on how to do this procedure and what the codes mean.
Q: My engine when cold has a very high idle rpm, but doesn’t come down much when warmed up, what is causing this?
A: Most likely you have a large vacuum leak. There are a lot of places in a corvette that can cause a vacuum leaks. However, the typical issue, but not limited to is the top plate gasket is possibly cracked or the top plates are lose or both. If the gasket is the original gasket, just replace it on a stock CFI motor. Also, the throttle body base gaskets could be leaking as well. The IACs provide idle control and there are two of them, one on each throttle body. These are essentially a ECM controlled vacuum leak to maintain a proper idle. If more air is coming into to the engine from somewhere else versus through the IACs, it is called unmetered air and the result is a high idle that doesn’t want to come down to normal idle. Ensure the IAC’s are cycling properly as well. Refer to the GM service manual for guidance.
Q: Will I see any appreciable increase in power porting my stock GM crossfire intake manifold?
A: Short answer is, Yes. You will see a good increase boost in power over the stock ports, but you must be careful when porting a stock manifold. The walls are a little thin and you can easily bust through into the water cavity and then you will have real issues. If you decide to port the manifold, go easy, slow and remove small amounts at a time. You will not see an equal boost in power compared to the Renegade manifold which was specifically designed for maximum power for any CFI engine.
Q: I hear a lot about balancing my throttle bodies, but how do I do it and is it really necessary?
A: The answer to “How To” balance your throttle bodies is an easy process and if you watch the two part series on throttle body balancing with the links below, you will understand how to do it and how simple it really is. Although the videos are not corvette specific, but use a water manometer just like the GM service manual uses, the videos are for crossfire injection and they are good videos. All crossfire injection engines run on the same principle, they need to be in balance with each other to run properly. Lots of people make it out to be rocket science, but it isn’t. Now, is it necessary? The short answer is Yes. The crossfire injection engines are both balance and fuel pressure sensitive. The balance part is to get both throttle bodies in unison with each other so that they both open and close together which will smooth out the idle quality. The fuel pressure is important so that you can feed the engine the proper fuel amount it needs to run and also under wide open throttle (WOT). The recommended amount of fuel pressure is 13psi by GM standards and the range is 9-13psi. Anything less than 12psi and the engine will not run to its full potential.
TB Balance Video Links
Q: My stock ECM is dead, what can I do to drive my corvette again?
A: This is an unfortunate situation, but it happens after almost 40 years of use with electronics that is in a closed box area next to a lead acid battery which the fumes after years of exposure to the ECM corrode electronics and connections. You won’t be able to drive your vehicle without an ECM (computer) controlling the engine. Also unfortunately, a stock ECM for the 82 and the 84 corvettes are extremely hard to find anymore and if you happen to find one, it may not be a good one. Even if a company refurbishes the ECM, they usually are bad or go bad quickly. Now for the good news. We no longer sell our famous HAM board (Harness Adapter Module), but it is incorporated into the EBL Flash II ECM which is the interface board between the newer style ECM along with the EBL Flash II from Dynamic EFI. This will let you retain your stock CFI system main harness and make you engine 100% laptop tunable. Another big advantage of doing this upgrade is that you can tune the engine to accommodate any mods that you happen to do down the road to include a NOS system if you wish. We also offer a FREE stock tune for the 82 and 84 corvettes to get you going right away and save you lots of tuning time. We also suggest going to an AGM style battery to eliminate the battery fume out-gas issue.
Q: Why do you have a 15% restocking fee now on returned items?
A: Short answer is, this was forced on us because of some unscrupulous customers who were taking advantage of us and using our products as troubleshooting aids because they couldn’t figure out what was wrong with their car. Then after using our products and finding the real fix were then saying that our products were defective and not as depicted and wanted their money back, when there was noting wrong with our products. So to that end, we had to start a 15% restocking fee on all returnable items that were not damaged or defective.
We make every effort when someone calls us about an issue to determine if they really need our products. I don’t want to sell anyone an item that they really don’t need, I don’t do business like that just to make a buck. Unfortunately, there are bad customers out there and I can’t fix stupid with any of our products.
Q: What does the TPS sensor do?
A. The TPS sensor is for idle. It tells the ECM where the throttle blade angle is in relation to idle. The TPS MUST be set to .525vdc at idle for best results. To set it, engine OFF, key to ON position. Loosen both screws slightly and adjust the sensor by moving it up/down while watching your volt meter for the proper voltage of .525vdc. You can purchase our TPS test harness in the Shop to make the task much easier. The procedure is in the GM service manual.
Q: I have a 84 corvette and want one of your fuel pressure assemblies, will a 82 corvette fuel pressure assembly work?
A: Technically the 82 fuel pressure assembly will bolt right on to your 84 throttle bodies with no issue and work fine. However, it will NOT work if you try to reinstall your 84 corvette air cleaner assembly. The air cleaner on a 82 corvette is completely different than a 84 corvette. If you look at the pictures in our Shop, you will see there is a difference in design for the two assemblies.