c4_4ya

Background:

Car starts, runs and can drive, sometimes a short distance, sometimes an hour or two, then suddenly dies. Usually it will start back up, sometimes it doesn't. It can usually idle for a long time no problems, but now it will idle for 15 minutes and will die, but will start back up.
Since the problem started, I've replaced the fuel pump, filter, HEI module, MAF, cap, and rotor.

OK, so I've been troubleshooting my 85 the last day or two (after it sitting since labor day). I hooked up a fuel pressure gage and here is what I understand:

- Car turned to ON, but engine off, fuel pump runs for 2 seconds and should give at least 40.5 lbs of pressure, which should hold steady, only dropping slightly and slowly. Mine reads right around 40, but then drops very rapidly down to 10 or less when the pump stops.

- With car running, pressure should read between 35-39 lbs, mine is around 30.

The possibilites are: bad fuel pressure regulator, bad fuel pump, clogged fuel filter, water in gas, clogged fuel lines, or bad fuel pump.

I recently replaced the fuel pump and filter, no change in the problem. I also added 2 bottles of the valvoline gas cleaner (supposed to remove water from gas) in a half tank of gas. I have ordered a new fuel pressure regulator and will put it in tomorrow and recheck pressure.

I tested all injectors with ohm-meter, every one of them measured 16 or 17, which is normal.

My question is this: if the problem persists after the new regulator is installed, I would think it would be a leaky injector. If I unplug the suspect injector, will it still leak or not, and what effect if any will it have on my fuel pressure? Also, will a leaking injector still read 16 or 17 on the ohmmeter?

I had one injector die on a Z28 I had with TPI and the car completely died, but when I unplugged the bad injector, car started and ran fine off 7 cylinders.

Also, if I need a new set of injectors, are the Accel 24# injectors good, or are they crap that need to be avoided?

Sorry if this is long-winded, but I tried to give as much detail as possible, I'm all but pulling my hair out over this one, and wanted to see what the more experienced mechanics in this group think!!

65Z01

You could check the regulator for leakage by putting a clamp on the return line near the tank filler.

Assuming the regulator does not fix the leakdown problem, pull the injectors and send the set (including the cold start injector) to Rich at Cruzin Performance (link on my site). He will clean, leak test and flow test them for around $100 or so plus shipping. Ship time is 48hrs from receipt of the injectors.

I had him reconditon and flow match the injectors in my '88 about 4yrs ago and a leakdown test a week ago showed they still hold rock steady.

c4_4ya

Thanks for the reply, but where exactly is the return line? All the fuel lines leading into the TPI are metal.

How do the 24# accel injectors stack up? Not that I don't like your advice, but the car has over 170K on it, and $300 bucks for a new set of 24# (instead of the stock 19#) injectors would seem to be a sound investment if they are good quality.

65Z01

When you remove the fuel filler door and the rubber boot you will see two lines going to the right and one to the left.

One of the lines to the right is the supply and the other the return; each line has a section of rubber tubing coupling the line to the fuel pump.

Clamp one of the right side lines, turn on the key while watching the fuel pressure gauge.
If there is not pressure increase, move the clamp to the other line.
If the pressure goes up and then drops as before, the problem is not with the FPR.

I understand your reasoning on the injectors; some of the guys here have used the 24# Ford injectors with good success but I think I've heard bad things about the Accel units.

c4_4ya

OK, here's an update:

Crimped the fuel feed line, no change, still close but not quite 40.5 psi.

Crimped the fuel return line and ran the pump, pressure shot up to about 75, then dropped back down to 10 or less in a few seconds. Why would it spike up that high if not a faulty FPR?

I will replace the FPR in the AM, if it's not that, it has to be a leaky injector. Anyone else wanna confirm or discredit my analysis? Any other suggestions? I appreciate any and all input!

BTW, thanks 65Z01!!

65Z01

The fuel pump delivers a constant volume of fuel; when pressure rises to the setpoint the regulator allows fuel to return to the tank so pressure is maintained at the setpoint.

When you block the return line pressure rises to the stall point of the pump.

Since the pressure dropped like a stone to 10psi after the pump shut off the regulator is ok and you have leaking injectors.

c4_4ya

I was kinda thinking that, but if that's the case, then here's my Q:

If I unplugged the injector, would it not leak anymore, thus causing the pressure to return to normal? Or is the idea that if it's leaking, it leaks no matter what? Also, would or would not the resistance read outside of the 16-17 range?

http://www.chevythunder.com/fuel_system_diagnosis.htm

According to this flowchart, here are my answers starting from upper left corner:

Not OK, pressure below 40.5 (maybe around 35-38 psi) (go to next chart)

Block fuel return line=pressure above 47 psi, leads to FPR

This sucks because my pressure is below 40.5, and does not hold.

If this is a leaking injector, is there an easy way to pinpoint which exact one? They all were in the 16-17 resistance range.

c4_4ya

Oh yeah,

If an injector was leaking bad enough to cause that kind of fuel pressure drop, wouldn't the car run minus that cylinder? When it runs, it runs fine and seems to have normal power, it just randomly dies and sometimes makes me tow it home.

65Z01

When you found that all injectors had resistance in the normal range that showed that the solenoid windings within the injectors were in good condition.

However, another failure mode is when an injector becomes clogged or worn and sticks slightly open. This is what leads to that rapid leakdown you see.

If only one injector is leaking badly you may be able to detect it by pulling and inspecting the plugs.

If that is not conclusive turn the ignition on/off several times with a 1minute dealy between switch cycles. If you cannot then smell fuel from one of the plug holes, remove the dist power wire and the two injector fuses (for an L98), crank the engine and recheck for fuel smell at a plug hole.

Some guys have unpluged the injector fuses, lifted the fuel rail enough to see the bottoms of the injectors and then turned the ignition On to prime the fuel rail and watch for a leaking injector.

There may be another issue that is causing the no start condition, but that can be adressed once you get fuel pressure to hold.

c4_4ya

Just got the new FPR, and I don't see how in the world it's supposed to replace the old one- I removed the black cover and there's a big spring mechanism inside... the new one is one piece and the directions say to discard the old cover but retain the screws and bracket (I assume the round disk with the 6 screw holes in it) and put it in, but the bracket is way bigger than the new FPR assembly... a little help here???

VetNutJim

Unplugging the injectors during this test will have no affect at all.

The injectors are only pulsed when the engine is turning.
They are just sitting there static until then.

During the 2 seconds of prime there is +12 volts to one connector on each injector.
The injector is turned on when the ECM Injector Driver circuit brings the other side close to ground.
Thus if you test the voltage on EACH side of the injector with the engine NOT running there will be +12 volts on each terminal because the driver circuit is not active.

The injector pintles are in their 'closed' position until the engine starts turning which turns the distributor which supplies the pulses to the ECM to allow it to 'fire' the injectors.

Did that make any sense? I think I confusededed myself.

When your engine cranks is it hard to start, smell like gass and blow black smoke out the exhaust? It it does you probably have a leaky injector (hope not).

I have NO experience with the Accell injectors but there are a lot of post with guys having problems with them.
Look for a set of FMS (Ford MotorSports) 24 lb injectors. A lot of us run those. They're CHEAPER too.

c4_4ya

Thanks for the explanation, it makes sense.

The car starts right up without any black smoke, but the blue smoke that's a sign of the notorious valve guide seals (when it sits a few days).

Would a leaking injector cause the car to run fine then just die with no stumbling, missing, or bucking first?

I think I'm just going to order the FMS 24# injectors and a crane adjustable FPR from summit- might as well do it all while I'm in there. My engine is stock (plans later down the road to up it a bit), are there any issues with the 24# FMS injectors?

c4_4ya

OK, so I have replaced all injectors with the ford 24#ers and new adjustable FPR, and new diaphram. Fuel pressure after switching the key on builds very slowly to 20 and maintains. After a few more cycles it gets up to about 42 or 43 then drops. It drops much slower than it did before, but still drops, eventually to zero.

Crimped the fuel feed line, no change. Crimped the fuel return line, no change.

Now the weird thing is, I started the car and the pressure steadily rose. I cut the engine off when it got to 70 psi, and it continued to rise to about 80, then dropped back down, eventually to zero.

I disconnected the fuel return line hose at the tank, and cycled the key to on several times to run the pump, and no fuel ever came out of it. (Don't know if any was supposed to either)

Little help?

want2drivemy85

Just for info..24# injectors came stock on 85 models. also, i had a fuel problem before also, i bought a replacement ac delco pump (pep boys) put it on and had the same problems...not enough fuel. long story short was that the new pump i bought was defective, and i replaced it with yet another one and all worked out fine. the ford injectors seem to work fine, there are quite a few people running them.

c4_4ya

OK backed the AFPR screw out and now fuel comes out of the return fuel line.

If I get the fuel pressure,with the car running, to maintain around 42 will everything be OK? This is driving me up the friggin wall!

Idling, fuel pressure holds steady at 42 psi. Car not running and trying to check the fuel pressure, remains very low and drops rapidly. Crimping the fuel feed or return makes no difference on the pressure.

Now getting codes 23 and 43, and car will die after a while of idling.

Any ideas???