Good idle, won't rev

[mboston]

Hello,
Been doing some engine work, replaced a rotten efi harnes, shot turbos and new 550cc injectors. Put the car back together, fired it up hesitates to start at first, maybe 5 cranks or so. After that it does idle well, around 900 to a thousand rpm, exhaust flow is smooth. But when the throttle is opened wide open, it will hesitate its way up to around 1800 rpm or so then drops to idle even with the throttle wide open. How ever it will only respond like this is you open the throttle quickly, if not it just does not respond at all. Has a strong vacuum, around -18 psi. Has a new fuel filter and upgraded pump 250 l/h I believe. I bypassed the fpcm thinking that was the problem. Suggestions? Thanks.

[nissanfreak12]

Do you have the ecu tuned for the 555's?


The normal checks;

ECU for codes
TPS to make sure its adjusted correctly
MAF if something wrong will limit rpms.
O2 sensors could also cause issues similar to this.

[mboston]

The ecu eprom, got it from concept z performance, was replaced to support the new injectors. I will clean out the maf and see how it acts. It could be the o2, they looked bad going in, I will disconnect them see if it runs better on a richer environment.

[mboston]

ECU put out 0 codes, only 55
TPS and CAS were adjusted appropriately.
MAF was cleaned and tested. .25 v at car on acc 1.5 volts car warmed and on idle
O2 senors were unplugged and the car did not react to the changes.

[nissanfreak12]

O2 sensors actually only work after 2k rpm. You can set the ECU in mode II, which tells you if they are turning off and on.

Are you sure all the plugs are on correctly? I turned the TPS plug backwards, caused the car to do some odd things, just a thought.

If all is good, contact COZ, possible problem could be with the tune. Been known to happen.

[mboston]

Probably will get in contact with them. I checked all the coil packs, spark plugs, connections, fuel pressure, pressure regulator. I even put the old Eprom back in, same results. So I am figuring that the new eprom does not have the right fuel maps for the new injectors.

[nissanfreak12]

If you used the old eprom chip and still did the same thing, you have another issue. Have you done a boost leak?

[mboston]

I checked. No vacuum or boost leaks. Thought I might have left shop rags in the plumbing, removed all of them and double checked. Nothing. Car was running prior to the upgrades and fixes. Here is what I swapped. EFI harness, Turbos, Fuel Injectors, Eprom. There some other items, but none that would affect the engine. EGR and some coolant lines under the plenum where damages so they were deleted.

[nissanfreak12]

Are you sure the turbos are spinning? Make sure nothing is lodged in them to create them from not spinning.

Measure the TPS when you open the throttle, backprobe the connector, leave it plugged in. Open it slowly to make sure there isn't a dead spot in it, best to use an analog multimeter.

Recheck all connectors, makes sure there is no contaminants in the plugs or sensors.

If all else has been done, and you used another ECU and had the same effect, chances could be the wiring harness is the culprit. Where did you purchase the harness from? Was it new or used? Basically process of elimination.

One more silly question, are you sure there isn't a break in throttle cable? Are you absolutely sure the throttle pedsl is connected to the throttle bodies? You didn't mix up the cruise and throttle cable? Don't think it would do anything, but doesn't hurt to look. Also, make sure the butterfly is actually opening, I think there was one guy where it only opened on the passenger side of the engine, not the driver causing all sorts of havoc.

[nissanfreak12]

One more thought, not sure if possible, are you sure you are installing the eprom correctly? Not backwards?

I re-read the post, actullay get a different ECU from someone if that is possible, try that out. Use a stock one if you can, don't drive it, just use it to start it and rev. It may smoke and run bad, but will let you know if that is the issue.

I think a NA one will work, but don't quote me on it. Like I said, don't drive it, just start and rev. You will know right away.

[mboston]

The harness is new, got it from Wiring Specialties. Pretty confident the eprom is installed correctly. The notch on the old eprom was facing to the right. Desoldered it, added a socket in the same orientation and the new eprom as well. IDK if the car would even idle the way it is if it was backwards? I will will check the TPS and if the turbos are spinning and if I can get a different ECU. The throttle cable is connected and moves the throttle body. Both butterflies open together. I was dissembling the engine again backtracking my steps and I noticed that the plastic connector to the alternator was not seated all the way in. If I am not mistaken, that goes to the battery charger? Would it affect the engines rev though?

[nissanfreak12]

You know, that could cause issues. The connection could tell the ECU there is no power to from the alternator and not let rev because its using limited power from just the battery. Just could be a hunch though. I do know cars run differently when the alternator is not plugged in. Some will not run at all.

[mboston]

Well, I will find out once the car goes back together, just waiting on some more parts to come in. In the mean while, do you know how to repair HKS SSQVs? have one that is sucking in air at idle,(Was removed way before the actual car problem), my only guess is the spring is worn out.

[mboston]

OK so. Reassembled the car, connected that alternator connector and air regulator (found this while taking the plenum off). did a boost leak test, installed the new fuel rails, made sure all lines where nice and tight. go to start her up, cranks no start. Sometimes it will start up, have to try to rev it to keep it alive or it dies. Now im getting a 34 code on the ecu, the knock sensor is new and so is the harness, going to bypass it for now. I made sure everything was connected. But now I am reading about 10 psi for fuel pressure (I had moved the pressure sensor behind the fuel regulator instead ahead of it, idk if this affects the reading). Any ideas? Thanks

[nissanfreak12]

You are probably getting code 34 because the engine is kncking enough for the sensor to pick it up. Low fuel pressure will create detonation.

Put the regulator back where its supposed to go, it will affect the reading. 10 psi will cause a hard start issue, if you put it all back the way it was before, still have low pressure, look at the regulator or pump. At least now it seems you can rev it, so you have some progress, hopefully.

[mboston]

OK so interesting fact. Moved my gauge in front of the fuel regulator. 43 psi when it primes and tries to start. and 10 psi after the regulator. so bad regulator? My guess is when i had stock injectors and rails, the regulator barley got by. Now that I have larger injectors and rails, it starves the engine.

[mboston]

Ok fixed that issue. The dampener and fuel regulator had their fuel lines swapped. But the original issue has returned. When car decides to turn over (hesitates while doing so), it idles very well. Fuel pressure is in the high 50s. When the accelerator is pushed, three things can happen. Either it dies, slowly climbs to 1500 rpm then slowly back down to idle, or it does not respond. You can hold it wide open, and it will idle. The tps is a .44v at closed throttle then reads a little of 4v with throttle wide open. Vacuum still strong, -18 psi when it idles. No boost leak. Strong fuel pressure as mentioned before. proper eprom for new injectors. The injectors work and you can even hear them ticking away as the car idles. The 34 code is still present. I stuck a screwdriver in the throttle body to hold it open and tried blowing compressed air through the MAS, car died. Im sure there is something simple causing this problem, to bad no one else is chiming with different solutions.

[nissanfreak12]

Odd question, are you sure your timing belt is correctly on? Set correctly?

Do you have a different TPS? Even though it test fine, could not be reading to the ECU correctly.

The reason no one is chiming because this is a very odd issue and have not dealt with it or really have nothing else to add because it would just be saying the same thing. I honestly have no clue what is causing this, but having you check things is basically brain storming, which eventually leads to the answer.

Since you have checked everything, I really think the wiring harness is wrong or wrong wires etc. It has happened, jut not normal. You can always find the diagram and go to town to make sure that they are correctly pinned.

[mboston]

The timing belt was done about a year ago by a local performance shop. I can remove the covers and confirm though. I don't have another TPS, Im going to see if I can read a signal at the ECU from it or get a consult cable. Even though I can get it to .44v. when I try to measure its resistance, 9kohms I believe, I get pretty much squat. I might be measuring wrong, will try again tomorrow. I figured as much and I do understand it is a very odd issue. Countless days of research and phone calls has told me that, ha. I appreciate you helping me and I am pretty sure soon the problem will be found.

[nissanfreak12]

Have you contacted wiring specialties? If not, maybe call them and talk to them. See if they have seen something like this or any idea. The main thing that was changed was the harness. They are great people, they will take care of you.

[mboston]

SOLVED! It was inter cooler piping. I have a FMIC although it is all open with no compartments, the fact that I had the same piping on both sides killed the airflow when it was accelerated. Thanks for you help!

[nissanfreak12]

Well that would do it. Glad you found the issue.

[Dave5442]

I’m sorry to revive this but I have the same exact issue and also have a fmic. I don’t understand what the fix was please help

[NolimitZ32]

follow your piping routing and make sure that it starts at the filter and ends at the throttlebody. The issue here was that the piping was routed incorrectly at the FMIC essentially deadheading the turbos.

[Dave5442]

I think I have them correctly, I have just after compressor housings both going to the 2 bottom ports, then the two top ports go to throttle bodies correct?

[NolimitZ32]

If you have a cross-flow (air flows side to side)


then you did the exact same thing wrong that the OP did, you are deadheading (forcing air out of the two turbos to fight each other and go nowhere).

If you have a vertical flow (air flows up or down)


then your setup is correct.

From your description you have a crossflow so yeah. . .

[Dave5442]

I feel so dumb thank you so much I’m gonna try this as soon as I get home. I really thought everything would be symmetrical there

[Dave5442]

Yup that was it, thanks again for the quick responses

[NolimitZ32]

No worries, glad I could help.