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Discussion Starter #1
So I recently reinstalled my s/c and was getting very lean AFRs. I bumped the fuel pressure from 50psi to 80psi and it got much better. Previously it was running great at 50psi. I measured voltage at the battery, fuel injectors and cigarette lighter. The battery and cigarette lighter socket were 14.1V however the injectors were only getting 12.7V. I've checked the positive/ground junctions on the firewall and the battery terminals and the ECU connection. I also checked to make sure the wiring harness didn't get pinched by the intake/supercharger after reinstallation.

Has anyone else experienced this or does anybody have any suggestions on anything else to check? :shrug:
 

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re: voltage at injectors

80psi is too high for the injectors and the fuel pump, at least it is on the ragged edge, if all is stock.

When you measure the voltage at the injectors, they are pulsing, so a regular voltmeter on DC setting would not give you the right reading. If you are getting 12.7V, it seems OK.

The only way to properly check the injector is with a scope and observe the actual wave-form in operation.

How much boost are you running? What is the device used to add more fuel with boost? Is it a stock S/C from Lotus? with the correct ECU? did you connect the MAP reference line to the fuel pressure regulator correctly? Maybe it is time for new bigger injectors and fuel pump?

Anton


So I recently reinstalled my s/c and was getting very lean AFRs. I bumped the fuel pressure from 50psi to 80psi and it got much better. Previously it was running great at 50psi. I measured voltage at the battery, fuel injectors and cigarette lighter. The battery and cigarette lighter socket were 14.1V however the injectors were only getting 12.7V. I've checked the positive/ground junctions on the firewall and the battery terminals and the ECU connection. I also checked to make sure the wiring harness didn't get pinched by the intake/supercharger after reinstallation.

Has anyone else experienced this or does anybody have any suggestions on anything else to check? :shrug:
 

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Discussion Starter #3
The injectors are bigger as is the fuel pump. Everything was sorted and running fine at 50psi. I replaced the s/c (with the same model) and then wasn't getting enough fuel. Turning up the fuel pressure proved this as it ran much better (able to take throttle). A friend (thanks Randy) tested the voltage on his Elise at the injectors with a volt meter like I did but was getting 14+ volts. Hence I think the problem is not getting enough voltage to the injectors. I just have no idea why? :shrug:
 

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Have you check'ed V in the fuse boxes?

The low injector V is 99% chance why you're running lean now and need the extra pressure as the bandaid... Just need to figure out where you're getting the V drop...

FWIW- the stock harness is known for being problematic. It's not a very good part... You could try jumpering a direct lead from known good power source to the green power loop that drives the injectors and see if that solves the issue... If it does, you could fashion a more permanent jumper to avoid having to replace the whole harness (assuming the issue is in the harness obviously-- which it probably is)...
 

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how does one increase the fuel pressure? I was under the impression that it was fixed and was dependent on the fuel pump (& injector combo).
 

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how does one increase the fuel pressure? I was under the impression that it was fixed and was dependent on the fuel pump (& injector combo).
Some people installed F.P regulators
 

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To the OP,
I would trust the guy that happens to use the right units on the Voltage, which is further evidence that he knows something.


and here he is:

...
When you measure the voltage at the injectors, they are pulsing, so a regular voltmeter on DC setting would not give you the right reading. If you are getting 12.7V, it seems OK.

The only way to properly check the injector is with a scope and observe the actual wave-form in operation.
...
 

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Yea injectors are actually current controlled devices interestingly enough. So as long as the voltage on the common wire is reasonable and solid when driving IMO you are barking up the wrong tree. In terms of checking voltage at the injectors just make sure you are checking the correct wire and a regular multimeter should work fine. Also be sure you pick a good ground to measure against ;)

Honestly I doubt the wiring magically went bad when you swapped blowers.

MAF is installed properly and clean? Are you sure you tightened all of the piping (particularly pre blower)? Also throttle body to blower gaskets are good as well as bolts are tightened properly?
 

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re: Fuel pressue

The fuel pressure is controlled by an fuel pressure regulator that bleeds excess pressure from the fuel line back into the tank. Hence, the fuel return line. The regulator is indexed to the intake manifold so as to maintain a constant pressure drop across the injector. The standard is 43psi or 3Bar. This is accomplished with a some kind of spring acting against a diaphragm against which manifold pressure is applied and a needle valve.

There are variations on this scheme. There are :

1. Adjustable FP's used in turbo and supercharged applications where you can turn a set-screw to adjust the pressure on the spring. So,if you run 5psi bbost, the fuel pressure is 48 psi, 7 psi would be 50 and so forth. A variation on that scheme is a rising-rate fp where the fuel pressure is incresed more than manifold pressure thus providing a very crude method of fuel enrichment under boost without changing the ECU. i.e. 5psi would lead to 50 and 10 to 60.

2. Fixed regulators are used by OEM's. They can be indexed to atmospheric pressure or just have no set-screw or can be just pre-set to a constan pressure since the intake manifold pressure variatio from idle to full throttle is only 15 psi.

3. Return-less fp systems are used in more modern cars, as they allow the manufacturer to save the expense of a return line. There are 2 types. One is using a regulator as a restrictor the other uses the ECU to precisely control the voltage to the pump to deliver just the right fuel pressure.

In all of the cases above, except the very last, the fuel pump is running at full speed. With the restrictor-type FP regulator, the pump is actually over-worked. The idea of controlling the FP voltage seems a very attractive one as it seems to put less stress on the pump. It has been used by Weldon for people that use really large pumps but still want to have reasonable fp at idle. The problem is the transition, if full throttle is applied suddenly, for the pump to speed up to where it needs to be required to over-voltage the pump and that wrecks it so much quicker :).

Injectors do not automize well at lower pressure, they also have trouble opening at higher pressure. Most are designed to operate at between 30 and 80 psi. There are different injector designs. I refer to Kinsler.com for a very detailed description of a good fuel system and detailed description of injectors and fuel pressure regulation.

All stock injectors are what is known as high impedence or peak and hold.

There are many fuel pumps. All of them deliver much less fuel as the required pressure goes up. Some of them cannot operate past 70 psi. The Walboro pumps are very good low volume high-pressure pumps, but at 80 psi none of them (and there are about 5 models) deliver enough gas for 200hp. Bosch -044 is good for 600hp at 70 psi and is used in most professional race cars. Weldon makes all kinds of nice high-volume pumps.

Anton

how does one increase the fuel pressure? I was under the impression that it was fixed and was dependent on the fuel pump (& injector combo).
 

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Injector diagnosis

I would run a simple diagnostic.

1. There should be a common wire running to all the injectors. It will be the same color to all. I believe, it is the common ground. With the ignition switch on but the engine not running, measure the voltage to the common wire against a good positive source e.g. + battery terminal. It should be whatever it is at the battery at all injectors. Repeat against a good ground for the other wires. Again you should get a good high reading. All readings should be the same at all injectors. If they are not, you have a wiring problem to that injector. If all the readings are the same, but the voltage is bad, check the common ground and then the ECU ground and power connections. This is a static test and it should check out very well. This test should indicate any gross wiring problem.

2. Now run the car and take the same measurements as in (1) by back-probing the injector connections. Again you should get a good reading on the common wire, just like in (2), if not you have a ground problem. You should get an even reading across the other wires, if one injector is not the same as the others, then its wiring or the injector is the problem. Next look at the reading from individual wires. The value of that reading would be hard to interpret, as it is a short DC pulse from the ECU. An even but low reading here can still indicate a wiring problem to he injectors or the ECU. the ECU supplies power to the injectors with high-powered transistors on the ECU board, so it needs good power source for them. If you suspect the wiring to the ECU you can try to measure the injector voltage at the ECU connector, it should be the same as at the injector.

If you are having a problem with all the injectors, then it should be the common ground wire or the power to the ECU. It would be very hard to blow up all the injector drivers at the same time. If you are manage to detect a problem with a single injector, you have an injector or an ECU problem. In either case, the faulty component would have to be replaced.

Anton

The injectors are bigger as is the fuel pump. Everything was sorted and running fine at 50psi. I replaced the s/c (with the same model) and then wasn't getting enough fuel. Turning up the fuel pressure proved this as it ran much better (able to take throttle). A friend (thanks Randy) tested the voltage on his Elise at the injectors with a volt meter like I did but was getting 14+ volts. Hence I think the problem is not getting enough voltage to the injectors. I just have no idea why? :shrug:
 

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Hmmmm

You guys are missing it.

The ECU completes grounds. It does not distribute power so it's not bad power to the ecu. There are common power wires for engine function. There is not a controlled positive supply to the injectors. It's just common 14.1 when car is running.

The ecu assumes if you will, the injectors are receiving the same voltage it is. there is a map in the ecu to compensate for low voltage. Well if the injectors are running lower voltage than the ecu it won't know to compensate for this.

There's something not right here.
 

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re: injectors

The logic above is still valid. Then the common wire should have positive voltage on it all the time. It should be the same as battery voltage.

Saying that ECU does some kind of analog voltage compensation to the injectors is not correct. Injectors are binary devices. They are on or off. The ECU drivers that drive them are composed of MOSFETS. They are very binary in nature also. So they are mostly on or off.

Then when the ignition is on but the engine is not running, the drivers would 'pull up' the individual wire voltage to +'ve battery voltage (to keep the injectors positively shut). This can be measured to make sure that there is a good connection to the ECU from all injectors. Also, if the drivers in the ECU are going bad, then they may leak and this test would show that as low voltage. So, that when the ECU grounds the injector (when engine is running), it would be ground well. The ground and power to the ECU is still important as any DC offset at that point would have a very strange effect on injector voltage.

ECU compensates for current electrical system voltage not by adjusting the voltage itself to the injector, but by lengthening the injector pulse duration. So at 10V battery voltage ECU would hold the injector open longer than at 14V. The ECU does a special calculation for that all the time.

Herein is the problem with measuring injector voltage when the car is running. They are being pulsed. On a DC setting the Voltmeter will measure some average value. The right way to measure would be to use the AC setting, but since there is a large DC component, it would probably blow up the rectifier in the voltmeter... If my initial static test does not show a problem, then a scope would be required to truly have a good diagnosis.

Again, we do not know what is even measure here. Static or dynamic voltage at the injector? All we know is some voltage is low and there is not enough fuel.

I had a similar problem and it took me a day to chase it down, although it was right in front of me. The car would start but not run. It had fuel, spark, but would just shut down. It was a bad MAP sensor, although it was brand new. The ECU thinks, no MAP, so no air, then engine does not need any fuel:) No power to injectors, and engien shuts down. It would start because during cranking the fuel and ignition is in static mode and ECU does the same thing all the time. I changed the MAP and the car started and ran great. I should have paid more attention to the tuning display when it was reporting too much vacuum :) So perhaps, check the MAF and connection here also.

Anton
 

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The ecu compensates Pw via ground signal for voltage.

He is unplugging the injectors one by one checking for voltage. The common positive is reading low.

There are several components on that common hot. The should all be checked of course.
 

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Hmmmm

You guys are missing it.

The ECU completes grounds. It does not distribute power so it's not bad power to the ecu. There are common power wires for engine function. There is not a controlled positive supply to the injectors. It's just common 14.1 when car is running.

The ecu assumes if you will, the injectors are receiving the same voltage it is. there is a map in the ecu to compensate for low voltage. Well if the injectors are running lower voltage than the ecu it won't know to compensate for this.

There's something not right here.
The table you are talking about is the injector offset table and dominates at idle and low speed cruises. At wot (where the op is having issues) a small 2v difference is the injector offset table is a moot point.

Again op before you even think about back probing and doing all this diagnosis on the injectors wiring please verify the pipes pre throttle body, and leaks around the throttle body and check the maf.
 

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Yes, I'm quite familiar with injector offset, but I disagree about only an issue at idle and part throttle. But you may be right in that it's not a voltage problem...

However, assuming he has checked the obvious stuff, and talking to him on the phone, he has.... The fact is that there's a 1.25ms injector offset from 14 to 12 volts on the EV-14 bosch injectors that he has. He's probably running 10ish ms at WOT. So if he's running 1-2 volts shy at the injectors from what the ECU sees, then using round numbers he's 5-10% short on injector PW since there's no applied injector offset by the ECU... Makes sense that bumping up the FP on his surge tank helps to bandaid this. It would take a MASSIVE air leak to create this kind of shortage. An air leak that would prevent the car from idling correctly, but the car runs fine in closed loop. It falls apart in open loop.

Can't deny that there's a problem in the electrical system if we're seeing this kind of resistance in such a short run of wire. IMO, until this all checks out correctly, there's a problem that needs to be resolved...

I have no illusions that I'm not the forum's best electrical trouble shooter, so please keep chiming in. I'm certain Jeff is looking for all the help he can get! As it relates to this ECU, just in this one thread there's a fair amount of wrong information, whether it be how ECU's control components or the way our car meters air. For instance, he doesn't have a MAP sensor and every EMS I know of for the Lotus completes grounds, MOTEC, EFI, stock, AEM, etc... In this case, it's a stock ECU that is MAF based, not speed density, for viewers at home...

Cheers,

Phil
 

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Yes, I'm quite familiar with injector offset, but I disagree about only an issue at idle and part throttle. But you may be right in that it's not a voltage problem...
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It would be pretty easy to run a big fat wire from the battery to the injectors to rule the voltage out.
That would require hacking something up.

But an oscilloscope would probably make more sense for figuring out the issues. If all the injectors are firing and all the plugs look about the same, then it makes sense to check elsewhere.

Modifying the tune with fuel pressure is less accurate than using a proper ECU. But no one wants to spend on an ECU when they could buy a bigger SC.
 

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FWIW- He has a "correct" tune that worked fine before the recent blower service...

Modifying the tune is a possibility, but you hate to do that when you know there's an existing problem...
 

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Yes, I'm quite familiar with injector offset, but I disagree about only an issue at idle and part throttle. But you may be right in that it's not a voltage problem...

However, assuming he has checked the obvious stuff, and talking to him on the phone, he has.... The fact is that there's a 1.25ms injector offset from 14 to 12 volts on the EV-14 bosch injectors that he has. He's probably running 10ish ms at WOT. So if he's running 1-2 volts shy at the injectors from what the ECU sees, then using round numbers he's 5-10% short on injector PW since there's no applied injector offset by the ECU... Makes sense that bumping up the FP on his surge tank helps to bandaid this. It would take a MASSIVE air leak to create this kind of shortage. An air leak that would prevent the car from idling correctly, but the car runs fine in closed loop. It falls apart in open loop.

Can't deny that there's a problem in the electrical system if we're seeing this kind of resistance in such a short run of wire. IMO, until this all checks out correctly, there's a problem that needs to be resolved...

I have no illusions that I'm not the forum's best electrical trouble shooter, so please keep chiming in. I'm certain Jeff is looking for all the help he can get! As it relates to this ECU, just in this one thread there's a fair amount of wrong information, whether it be how ECU's control components or the way our car meters air. For instance, he doesn't have a MAP sensor and every EMS I know of for the Lotus completes grounds, MOTEC, EFI, stock, AEM, etc... In this case, it's a stock ECU that is MAF based, not speed density, for viewers at home...

Cheers,

Phil
Hold on to your calculators people!

First things first the difference between 14.1 and 12.7 is about 1.4 volts.
And at those voltage levels we are talking about a difference of maybe 200us (that would be 0.2ms) of injector offset.

So at a pulsewidth of 10ms that is:
0.2/10 = 2%

Like I said moot point.

Also fwiw I've been telling him to check his MAF (not map) and also check for leaks between the maf and tb
 

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I know YOU didn't say MAP;)

Not seeing the 2%. If 2 volts is 1.25ms, which it is on those injectors, how is 1.4 discrepancy only .2ms? It's not a perfectly linear scale, but it's close enough for forum work...

Regardless there's a problem with the electrical system there... He has checked the MAF...

I'm not trying to be a closed book on it, I just don't see how/why we're dismissing a 1.4volt drop in current in ~4 feet of wiring...
 

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I know YOU didn't say MAP;)

Not seeing the 2%. If 2 volts is 1.25ms, which it is on those injectors, how is 1.4 discrepancy only .2ms? It's not a perfectly linear scale, but it's close enough for forum work...

Regardless there's a problem with the electrical system there... He has checked the MAF...

I'm not trying to be a closed book on it, I just don't see how/why we're dismissing a 1.4volt drop in current in ~4 feet of wiring...
You need to double check your injector latency data.

There may be a TOTAL of 1.25ms (which BTW is questionable) at say 14 volts. But no way is it 2.5ms (a delta of 1.25ms like you are claiming) at 12.7v
 
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