I have a 1985 Camaro with a 383, HSR and 1990 Camaro ECM installed. 30 lb. injectors, Walbro fuel pump (everything new).

I have a (mostly) cold hesitation and partial throttle, I posted regarding this before.

I installed an inline fuel pressure gauge this weekend. When I turn the key on (not start the car, just turn the key), the pressure immediately goes to 51-52 PSI but bleeds back down to zero in the matter of seconds (as soon as the pump turns off). Is this normal?

With the engine running at idle (about 1,000 RPM), the pressure is constant at around 50-51 psi. I'm having a hard time digging up the specs for the HSR, but I think this is either at the upper end of the recommended pressure or slightly higher.

I haven't checked the PSI at any RPM other than idle - I plan on doing that later. It shouldn't be any different at higher RPM's, should it?

Thanks in advance for any replies.

 

Whats the fuel pressure at idle with the vacuum line plugged in?

As far as the pressure dropping when the car is off. It will have no affect on the way the car runs. All it might do is make it take a little longer to start.

If you have a hesitation when cold and part throttle it's most likely in the tune.

 

The pressure posted above - 50/51 psi - is with the vacuum plugged into the regulator. I haven't checked it without it plugged in. Should I?

I couldn't find anyone local to tune it, so I went the mail route. I datalogged three times, sent them the file & then received a tune from them and re-burned the chip. They tell me that the tune is as good as they can get it.

I have all of the datalogs, is there something I can look at in there that would tell me if it's not getting enough fuel at certain times or whatever?

 

Your regulator might no be working properly or it's not making enough vacuum at idle to lower the fuel pressure down. Which I guess is possible but I have never actually seen.
The pressure should be basically the same with the engine off or with it running with the line disconnected. With the line hooked up it should go down. How much depends on the vacuum.
Rev the engine and see if the pressure changes. If it doesn't then you have a bad regulator.
O and fuel pressure specs are from the ecu you are running not the intake setup. Unless the programmer tuned it for a different fuel pressure you should set it to the stock fuel pressure for the ecu which you said is a 90 camaro. But check with your tuner first for the recommended fuel pressure.

 

There's no fuel pressure "spec" "for the HSR". All it is, is a chunk of aluminum. It doesn't care what the FP is.

FP is a tuning thing; you use its setting to get the correct amount of fuel delivered at a reasonable duty cycle by the particular injectors you have, for the particular engine you have with its fueling requirements, and within the range that the ECM is expecting the DC to be to get the O2 reading where it expects that to be.

30 lb/hr sounds like too much injector for a motor that small. Try backing the FP WAY WAY off; like, to 43 psi, with the vac unplugged (which is how you're supposed to set it in the first place); and see what happens.

It's called TUNING. You make adjustments and see if they help, until any adjustment in any direction makes it worse (that is, until it's the best it can possibly be). It is NOT, look up some "spec" in some "book" somewhere and "set" to the "spec".

 

Okay, well, I'm dumb. I bought a FP gauge that looked nice and while it works, it's hard to see the numbers. What I posted earlier was wrong.

At idle, with the vacuum line hooked up, it's at 40-41 PSI (not 50-51 as I stated before).

When I rev it up or hold the idle up, the pressure drops to about 37 or 38 PSI, it never goes lower than that. As soon as I let off the gas, it goes right back up to 40-41.

I unplugged the vacuum line, tried starting the car - it cranked and cranked and cranked and eventually caught and started (not sure if this is normal when you unplug the vacuum line or not - I did use a plug so no vacuum leak). When it did, the fuel pressure was steady at 40-41 PSI and never moved when I revved it or held the idle up. I think this means the regulator is okay, right?

Now I'm wondering if I should bump up the fuel pressure a little? Or is 40-41 okay?

 

Bump it up and see. If you don't like it, bump it back down, and then some more.

Which letter of which word can I explain more fully, that will help you understand to PUT DOWN THE GAUGE AND QUIT FUTZING WITH A BUNCH OF "NUMBERS", AND PICK UP THE SCREWDRIVER?

 

Okay, point taken...I'm new at this and still have "the fear" of screwing something up & not being able to bring it back, doing long term damage or just generally wasting my time on changing/working on something that won't make a difference.

As soon (if?) the weather breaks here & it stops raining, I'll pull the car into the driveway and start TUNING!

 

I played around with the pressure a bit today. I was surprised, the numbers I got today were different than yesterday. With everything hooked up, the pressure was 39-40 PSI at idle, when holding the RPM's up it would drop to about 36. Seemed low to me.

I adjusted it to 42 PSI, with the vacuum line hooked back up it was still at around 39-40 and again was dropping to around 36. Took the car for a ride, no noticeable difference. Adjusted it again to 45 PSI, which vacuum hooked back up it was at 42 at idle and 40 at higher RPM. That's when the rain/thunder/lightning hit, so I didn't get a chance to take it for a spin. I'll do that tomorrow. Two questions:

1) Am I going to hurt anything if push the pressure higher and test it? If I took it all the way up to 50 PSI without vacuum - am I going to kill the regulator or injectors or anything like that?

2) Is there any benefit to doing a test drive with the vacuum line disconnected?

Thanks.

 

No you will not hurt anything.

Adjust it and see what happens.

If it "drops", "changes", isn't "the same as yesterday", "surprised", is "different" but you don't know why, fix all that first. Get it to where you KNOW from minute to minute that you made X change and got Y results, and you can duplicate it reliably. Not a lot of point in attempting to "tune" something that changes randomly apart from whatever adjustments you deliberately apply to it.

No, no benefit to driving it with the vac line disconnected; unless you just want to see what it will act like with about 7 - 10 psi too much fuel pressure at all times EXCEPT when you're at WOT. I guess that might give you a hint as to whether you have too much, or too little, FP; if it gets better you don't have enough, if it gets worse you have too much.

This is JUST NOT THAT HARD. Make a change, understand what that change REALLY results in, evaluate the results, go from there.

 

Good point about the changes, etc.

Agree that in general, this isn't (or shouldn't be) difficult; the problem is, I sort of feel like I'm chasing my tail or going in circles.

I spoke to the company that did the chip tuning, they said that they want the fuel pressure and timing set to stock. From what I can find, stock fuel pressure is 43.5 PSI with the vacuum line unhooked. I was at about 40, so that's where the tune was done.

Of course, I can adjust/drive/adjust, but suppose I get done and I'm at 46. Do I leave it? Or do I datalog & get the chip tuned again at 46? Or do I set it at stock now, get a chip tune and then drive/adjust until it's maximized? Seems like I could go around and around. Not sure how much a chip tune changes between 40 and 43.5 PSI, either - I might be talking about nothing.

 

You should leave it wherever it runs the best. If that is within the "reasonable" range for injector performance, then the fact that it's slightly different from "stock", doesn't necessitate chip changes. Other things might; but that, by itself, doesn't.

Keep in mind, all injectors have a tolerance, as do all gauges. Whoever burned your chip might have assumed your injectors flow 22 lbs/hr, but maybe they only flow 21.5. And/or, maybe your gauge is a few % off; when it says 43, it's REALLY 44.5. Who knows?

Now if you discover that you have to set the FP to 36 or 52 or something on the fringe like that, then maybe you'd want to do some chip work; or, maybe just change the injectors.

Flow changes roughly with the square of changes in FP. I.e. if the FP is 10% higher, the flow will be near 21% greater. (1.1 × 1.1 = 1.21)

Tuning that sort of thing is a little like working out at the gym: you design a situation where the car's behavior is the most sensitive to the one thing you're working on at the moment, with as few as possible inputs from anything else, and you tune that one thing. Just like "isolating" a muscle at the gym. Then once that ONE THING is optimized, you "isolate" the next characteristic, and tune that one. Since in a crude old batch-fire system like TPI the pulse width is fixed at WOT, it's best to FIRST tune the FP at WOT (for best mph in the ¼ usually) and then see where it lands, which will then tell you if the injectors are the right size; then look at BLMs and such to see whether the rest of the tune is within reason.

 

Take it to a drag strip or find a shop with a chassis dyno. This way you can really tune it or have it tuned.

On the driveway and street is not tuning because "seat of the pants" is not real data.

You are getting hung up on fuel pressure... which is not tuning.. Set the fuel pressure to specs once in a certain range this will not make or break the car.

Tuning is fuel curve and ignition timing.

If you are timid or unsure about tuning find a shop with a chassis dyno
and they can help dial-in the tune on the dyno. At least give you real data to work with (HP, TQ, MPH, RPM, A/F ratio)

if you have a factory ECM a baseline tune should get you close because the factory ECM has some "self tuning" ability, I think you just need to drive the car.

The problem with the stock ECM is you cannot tune on the fly with a laptop... the chip needs to be recalibrated.

 

I re-read OP post

if you have data logs... then you need to look at

A/F (O2 READINGS) .8 at WOT , 1 at idle / part throttle since you have a narrow band O2 .8 has a very broad range... so you could fatten or lean the fuel map to a degrees and still be showing .8 reading which is ok... but anything less than .8 is way too rich... .7 .6 .5 means you need to pull fuel out of IV map

IV (injection volume or fuel map) I don't know your cam, head specs...
but you can make judgement based on O2 readings and MPH at the drag strip. tune for best MPH. if you are "rich" pull out some fuel if the car speeds up pull out a little more... keep doing this until MPH slows down. if you slow down go back to previous setting this will be best "jetting" aka fuel curve aka fuel map aka IV for your WOT.

Timing: should be no more than 36 degrees total with a 383
what is your timing curve like? how much timing at idle ?
idle & part throttle should be between 16-19 degrees.
Total timing should be all in by 3000 RPM.
again you can dial in timing by tuning for best MPH.


trusting a mail order tuner is a bad deal they will only help you so much...
to say it's the best they can do is any easy way out for them.


I used to play with a 383 in my car with 465 HP. I hade Projection 4Di system, I don't now how radical of a cam or heads you have... but fuel is fuel... I could look to see if I have my old fuel maps. I switched to CARB on my new setup.

OR try Contacting Arizona Speed and Marine they were vey good back in the day. they may help you via email..

If this is way too much for you find a shop with a chassis dyno that knows how to tune. Even if you have to trailer the car there and spend the day it will be well worth the effort. otherwise the tune will never be right.

 

I would love to try to find someone local to help me, but (surprisingly) I have yet to find a shop that can do a dyno tune on my car. There isn't a lot of places around to begin with and the ones I've called only work on newer models.

When I get home, I'll review the data logs. If the weather holds, I'm also going to take the car for a spin now that I've upped the pressure a little bit.

Thanks for the response & all of the information.

 

They want to work on newer models only because of the OBDII connection

 

Yep. My brother owns a repair shop (no dyno), he has a Snap-On scanner that can hook to my car & read the data but it's not very in-depth...in fact, I think there is less info on that than there is in my datalog. On the newer cars, it can read everything.

 

I keep meaning to ask this & I forget. Based on what I'm seeing, does it appear my fuel pressure regulator is working okay?

Once adjusted, the fuel pressure (at idle) drops about 3-4 PSI once the vacuum is hooked back up; at partial throttle or when revving it up, the pressure drops another 3-4 PSI. Is this normal for the regulator? There is so much information regarding this, some people have posted less of a drop, more of a drop, etc. Just want to make sure the regulator itself is doing it's job correctly before proceeding with adjustments/tuning.

 

Yes that is normal.

The amount that the pressure changes, depends on the vacuum at that moment; the more vacuum, the lower the pressure.

Remember, the flow through the injector is proportional to the pressure difference across its valve - that is, to the difference between the absolute fuel pressure and the pressure inside the manifold - which if you have, say 15" of vacuum, then that's about 7½ psi lower than atmospheric (1 atm being just under 15 psi, and 30" of mercury); and the purpose of the vac ctrld FPR is to back the FP off by that exact amount (or close to it) so that the absolute pressure difference across the injector is always about the same.

 

That being said if you have data logging software and can re-burn the chip then all you need is shop with a chassis dyno that can interpret your data logs and dial-in your tune.

Besides this a dyno-jet will have a wideband O2 sensor so they take out your narrow band sensor to get actual WOT A/F readings..

Did you explain this to the shop owners you contacted? that you have the datalogging and chip burning equipment?

A true tuner with a dyno will not turn away work.


Otherwise do it yourself at the dragstrip tune for best MPH.. as described before. if you have a knock sensor you don't even have to waste time reading spark plugs. since detonation should not be an issue...

If you a looking for "street" driveability a chassis dyno is better since they can hold the rpm to tune part & mid-throttle, not just idle & WOT. you could do this on the street but unsafe unless you have a co-pilot.

Don't get geeked out on fuel pressure you have more important items to sort out.

 

Thanks for the response. No, I don't think I explained to shops that I had the data logging and chip burning capability. However, I usually didn't even get that far. Once they heard "85 Camaro", it was no dice. I might try again, though.

Yes, I do have the knock sensor.

I think my fuel pressure is fine. I played around with it today, I took it really high (the car ran bad in general) and pretty low (same), but right around 43-44 with no vacuum it seemed to run the best. However, my hesitation is still there.

I'm not sure if this is the best place to post this, or if this should be a new thread, but I also checked my vacuum and timing today. The vacuum seems fine, about 15 in. at idle and goes up to 17-18 at higher RPM. At idle, it bounced a little (maybe between 14-16) but at high RPM was very steady.

My timing, on the other hand...no idea what to make of this, I just don't enough about timing to know if this is normal. Back when I set it when the engine was first installed, I started the car, disconnected the timing plug (remember, this is the wiring harness & ECM out of a 1990) and set the timing to 8. Plugged the timing connector back in and away I went - I wasn't smart enough to check the timing after that.

So today, I check the timing with the connector plugged in - it's at 28. I disconnected the plug and checked it, it's between 9 or 10. Plugged the connector back in, it stayed at 9 or 10 and my engine light was on. Shut the car off & restarted, light was off and timing was back to 28. I then held the idle up and checked it, I don't know exactly what RPM I was at because I was doing this by myself from under the hood but I kept creeping higher and higher until the timing stopped changing. Based on the sound, I'm guessing I was around 3,000 or 3,500 RPM. Anyway, at that point my timing was at 52 or 53. Is this normal?

One more question, going back to my hesitation. I was paying more attention today and noticed that my two issues may be two separate things (or one thing causing two different symptoms). The two symptoms:

1) When pulling away from a dead stop slowly and the car bogs down/hesitates, the tach doesn't move - if I'm at 2,000 RPM, the car will start to sputter and jump a little but the tach stays right at 2,000 RPM. Does this point to anything?

2) While driving, if I'm going 35 or whatever and give it just a little gas to maintain speed, the RPM will start to jump up and down, like from 1,400 to 1,700 then back to 1,400, back to 1,700, etc. You can hear and feel this, too. When this happens, if you give it more gas it immediately goes and the jumping goes away.