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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Was wondering if I chose the wrong fuel setup using THIS adjustable fuel pressure regulator for my EFI setup using a EBL P4 ECM batch fired injectors. I currently have it adjusted to 44psi when I switch the key on. I have all new parts like injectors, fuel filter, fuel pressure regulator, etc.
I chose the bottom setup just because it was the easiest and I'm new to this type of stuff. I'm seeing steady pressure at the gauge on the adj regulator with the engine idling but when I hit the gas the pressure drops down to about 30, maybe less depending on how hard I hit the throttle.
Did I pick the wrong setup? I know this doesn't match the original 1986 TPI setup which is probably more like the middle setup in the pic. Looking for concrete answers if possible, thanks.
You're running it on a port injection setup right? That should be fine typically you set it to 43-44 PSI with the vacuum disconnected although you may do higher or lower base pressure. After that connecting the line the fuel pressure should drop based on the engine vacuum.
There is a risk that you're dropping fuel pressure if your pump is marginal. Is it a stock pump or is it an aftermarket pump? I could see your pump being marginal for that engine but I'd think it would roll off under acceleration.
You're running it on a port injection setup right? That should be fine typically you set it to 43-44 PSI with the vacuum disconnected although you may do higher or lower base pressure. After that connecting the line the fuel pressure should drop based on the engine vacuum.
There is a risk that you're dropping fuel pressure if your pump is marginal. Is it a stock pump or is it an aftermarket pump? I could see your pump being marginal for that engine but I'd think it would roll off under acceleration.
Thanks for your input.
Yes, stock pump and also no vacuum signal present to the fuel regulator...
I'm just thinking when the fuel pressure drops like that it will screw with what the ECM is expecting from the O2 sensor(s) and also what I've put in the ECM for the flow rate. In my case it's 42lb. But I'm thinking it's not 42lb flow rate if the pressure can't be maintained @42lb. This is what I'm worried about. BTW these are the Bosch green 42lb injectors.
do you know how much vacuum at idle you're pulling? Typically you subtract the amount of vacuum it's pulling from the base fuel pressure and that's your new fuel pressure. As an example if I'm pulling 20inhg (basically a stock cam) you'll drop about 10 PSI. I wouldn't want to try and run a 500HP engine on a stock fuel pump. I'd be looking for an Aeromotive or Walbro 255lph or 340 LPH or similar and a hot wire kit home made or commercially made.
Right, I agree with you. I was told a stock pump might be good to 400HP...
The thing that bothers me is the fluctuation in pressure vs throttle. It's not steady, so flow rate will not be steady (I would assume) and the ECM won't know what's going on.
NO! That is absolutely not the right way to plumb your rails. You need to use #1 or #2 AND you need to have a vacuum reference to the regulator.
It should be set to 43.5psi with the vacuum line disconnected, and with it hooked up it should idle around 33.5psi (or whatever your idle vacuum is subtracted from 43.5), and when you blip the throttle the pressure should RISE back up to 43.5
Tuning will be more difficult without pressure across the injector being held constant by using the vacuum signal, and you don't want to dead-head the rail like #3 - the regulator isn't going to react fast enough to maintain pressure accurately.
What are you using for tuning?
Also - that's a crap regulator. Here's a good one:
I'd put a pump in it before I went anywhere else honestly. No use even bothering to troubleshoot the rest except maybe disconnect the vac line from the intake, plug it up and see if the FP drops when you're revving (either not enough pump, too much fuel system restriction or both.) I'd be curious to see how even it was bank to bank. That said the LS stuff is set up pretty much that way too and people turbo those to a ton of HP without much issue.
If your pump is healthy, it will be fine as you get into your early stages of tuning, but when you start to lean on it, you'll need the 255 pump. You really need a setup like number 1. For a few reasons, keeping cold fuel flowing through the lines, instead of dead heading in the hot fuel rails, as well as having the regulator after the rails, so you can get a more constant, uninterrupted flow of fuel through the rails from the pump. Shoot me a text if you have any more questions. I can walk you through doing a test on your pump if your shop has a modis or verus and low amp clamp.
NO! That is absolutely not the right way to plumb your rails. You need to use #1 or #2 AND you need to have a vacuum reference to the regulator.
It should be set to 43.5psi with the vacuum line disconnected, and with it hooked up it should idle around 33.5psi (or whatever your idle vacuum is subtracted from 43.5), and when you blip the throttle the pressure should RISE back up to 43.5
Tuning will be more difficult without pressure across the injector being held constant by using the vacuum signal, and you don't want to dead-head the rail like #3 - the regulator isn't going to react fast enough to maintain pressure accurately.
What are you using for tuning?
Also - that's a crap regulator. Here's a good one:
Aeromotive 13301 https://www.summitracing.com/parts/aei-13301
Walbro 255lph https://www.summitracing.com/parts/vpn-gca758-2
You need the vacuum attached for Idle, low throttle and deceleration. Tuning VE with vacuum attached will integrate the fuel pressure curve into your tune. Since the fuel pressure curve stays constant, once integrated into tuning, it'll never vary.
Aeromotive 13301 https://www.summitracing.com/parts/aei-13301
Walbro 255lph https://www.summitracing.com/parts/vpn-gca758-2
You need the vacuum attached for Idle, low throttle and deceleration. Tuning VE with vacuum attached will integrate the fuel pressure curve into your tune. Since the fuel pressure curve stays constant, once integrated into tuning, it'll never vary.
We have seen some really poor machining inside the Aeromotive pumps of late. I steer people away from them now.
Walbro's are good but REALLY loud compared to the AEM or Deatschwerks pumps. AEM has silent E85 compatible 340 LPH pumps for cheap - like $100 or so.
AEM 340 in my project so far no complaints. Considerably quieter than a GSS307 I had before. That said I'd have no trouble running them too. I'd be sure to get a real one not a knockoff e.g. not an ebay or amazon pump probably.
If your pump is healthy, it will be fine as you get into your early stages of tuning, but when you start to lean on it, you'll need the 255 pump. You really need a setup like number 1. For a few reasons, keeping cold fuel flowing through the lines, instead of dead heading in the hot fuel rails, as well as having the regulator after the rails, so you can get a more constant, uninterrupted flow of fuel through the rails from the pump. Shoot me a text if you have any more questions. I can walk you through doing a test on your pump if your shop has a modi verus and low amp clamp.
The pump is good. When the 305 was in there, I could WOT from a stop and the car would do great. I'm just trying to sort out my tuning issues and from the sound of it, the engine should at least idle. When I can get it running, I'll definitely move on to a walbro pump and try to correct the fuel flow setup to the top of that pic in the head post.
I really appreciate all your advice!
Last edited by UltRoadWarrior9; May 12, 2020 at 02:54 PM.
