So has anyone troubleshoot for a leaking injector, by pulling a spark plug and looking for a wet tip? Im talking about after a KO-EO, and watching for the pressure to bleed off. Mine goes down to ~10psi after a few minutes. First i pinched off the supply line, and it still bleeds down the same way. Then pinched off the return line, and it still bleeds down the same way. Shop manual points to leaking injectors, and to pull plugs and look for a wet tip.

I still have the original multecs, but they have been serviced 3 times, since i bought the car in 1992. Twice at Cruzin Performance, and the most recent in August of 2015 at FIC. Way back one was found to be a "dripper". Car runs great, no issues, sort of. The one main issue i have, is that i have long engine cranks, after a few hours, from hot engine shutdown. I can give it a little throttle, during long cranks, and it helps it to start right up. Cold engine starts are perfect. So i am leaning towards a flooded engine, creating long cranks, and giving it a little air helps.
Thoughts?

 

Replace the garbage multecs with some new Delphi's. No tuning required.

GD

 

I respect your advice, but it does not address my question. I will likely go with Bosch type III units, the 24lb'ers. I do my own chips, so i can set the FIC to whatever is correct for my fuel pressure. I know the early multecs were trouble, but i think in 88 they were better. I would just like to prove that they are leaking before i rip them all out. I have the Bosch III units in my '90 C4, and am quite happy with them.

 

You can't really "prove" it. You can pull plugs as you suggest and possibly get an idea from that. A lot of trouble to go to.... some intake valves may be closed so you will probably have to repeat that process multiple times. Time delay between pressurizing the rail and pulling plugs - which valves are closed? It's going to come down to a solid "maybe"...... to really "prove" it you pull the injectors out and put them in an injector test bench and see if they drip, etc. But really at that point just throw them over the nearest fence and swap in some new injectors that aren't going to potentially have a driver coil failure or start leaking down. Having an old injector randomly go lean is a great way to melt a piston.

The Bosch III's are great at being cheap, being loud, and being a pain to find offsets for. If that's what you want to spend your time doing then go for it. Me - I bill my time out at $99 an hour. I will spend more than a couple hours (the difference in price for the Dephi's) burning chips and screwing with latency tables on an ECM never designed to run those injectors. I've got a set of them in my daily driver and honesty they aren't worth the trouble. They run fine after adjusting everything and actually TESTING the voltage latencys.... And the infernal NOISE of those things being batch fired is enough to drive a man insane. IMO you get what you pay for with the Bosch III's. I still get people asking about my "bad lifter"....... it's super annoying.

It all adds up to a BIG FAT waste of time. Yank them, toss them in the nearest round file, put in some QUALITY DIRECT REPLACEMENTS, and then focus on other things that will actually take you forward not sideways.

GD

 

Well said!

 

don't waste time, money, energy, and yer car, do what this man says....

 

Well now, that is interesting. Didnt think Bosch made cheap automotive parts........I have had the Bosch III units in my C4 for like 6 years now, and no issues. And i havent changed any injector offsets, just the FIC for the FP i am running. As far as being noisey, mine arent. When any engine is running, its gonna make noise........just saying. Car runs great. The Delphi units are more than 2x the cost of the Bosch III units. (they look like re-designed Multecs) If my memory is any good, the yellow 22 lb units were the ones to avoid.

The other test i could do, is to lift the rail up, with everything still connected, and hit the key on to run the pump. And watch for drippers. That test could get messy, have to come up with some catch-cans for the fuel. I dont mind spending $$ on my IROC, just not for the heck of it........

 

If you checked out BLM's on the C4 you would likely find that more tuning is required for the DIII's. Injector voltage compensation and also they generally don't run correctly at the advertised flow rate due to how the ECM handles them. And they are VERY loud in the TPI cars, They click when opening and when batch fired in the TPI cars, all 8 of them open at the same time. Makes them quite loud and it sounds like a bad lifter in operation. If you can't hear that then I can only guess that the engine is noisy in some other way that masks it. Everything else on mine is quiet (except the exhaust which is at the other end of the car out of pure necessity).

It's not that they are "cheap parts" per-se. It's that they are old - what you are buying is a used injector that's been "reconditioned" - which means cleaned and flow tested. That's why they are "cheap" to buy. They aren't particularly cheaply manufactured. They are old, I don't believe they are manufactured anymore (Bosch makes EV6/EV14's now for the most part), and they are LOUD A.F. The price reflects the used nature of the parts. And they are good injectors - reliable, and much better performing than the Multec's.... when used in their correct original applications. They are loud in a batch fire environment, and require tuning for TPI applications to perform at their best.

The price of the Delphi's is because they are NOT reconditioned. They are new injectors designed to be direct replacements for the Multec's. The price reflects that you are buying a new part not a used one, and supply/demand for these is lower so that's also reflected in the price.

GD

 

^ Preach

 

Could still leak back from the FPR. Suck/smell the vac line going to it.

 

Appreciate GD's and SouthBay's posts and respect their opinions. But I have FIC BIIIs (B3s) so will weigh in. Yes, B3s are louder than Multecs and most other injectors, but can only hear them with head under hood--not in car. The FIC dual O-ring at the manifold side appears to absorb the noise. Delphi's also VG but at a cost some may not wish to pay.

Another comment. To say that no tuning will be required when replacing Multecs with B3s or others is debatable, even when a #-for-# flow rate change is made. It's widely accepted when replacing Multecs with B3s that the low PW Table Table (essentially the injector idle area), be zeroed. Why? Because the B3s provide more fuel. The code-commanded pulse width (injector open time) does not change, but the amount of fuel during that time does due the superiority of the injectors. That means VE/MAF changes may be required to correct a rich condition. Ditto for above-idle. It would follow that the superior spray pattern of X# flow rate B3s, combined with the fact that the Multecs are 25+ years old and likely not flowing at X#, will cause more fuel to also be delivered during the above-idle open-time.

I just completed a #-for-# flow rate SD TPI Multec to B3 conversion and my experience was just that. Had to lean VE tables everywhere, especially at idle.

B3s, Delphis, etc. Maybe that's why there's both chocolate and vanilla ice cream.

And to the OP's question, my bet is that the fuel pump is not holding pressure. At one point, I had same problem you described. Cold start OK, hot took a while. Installed one way check valve on supply line and all is good (Russell 650603). Russell a little more expensive than others but has a 304 stainless check system as opposed to a rubber flapper.

One trick that helps in a pressure bleed-off situation is to start cranking while the pump is priming which is the point of maximum pressure unless significant fuel system issues. If you wait until it primes and shuts off and you have a major pressure drop, you may have less than required fuel pressure until the ECM detects enough reference pulses to turn on the pump again while cranking. See also: https://www.thirdgen.org/forums/tpi/...ml#post4573239

 

The modern turbine pumps do not have check valves, and are not positive displacement so pressure bleeds off when they aren't running. That's normal for them and at least one manufacturer (AEM) suggests adding a check valve on older vehicles that expect a positive displacement roller-vane type of pump.

GD

 

With how fast the line pressurizes, its usually not an issue with the lack of a check valve; lots of people misdiagnose it as leaky injectors and its just how new pumps work (as you state). Mainly just saying that for posterity's sake.

I do agree with the above sentiment to crank it while its priming for best result.

 

GD, I currently have a Deatschwerks turbine pump with a check valve. Works great. The only issue was the modification I had to make to the sending unit to hang the pump because it's slightly different than the factory Delco, but nothing major. This is a company that is under the radar with great products and outstanding customer service.

 

Oh yeah we use the DW200 and DW300 pumps quite often. I have one in my 86 Trans Am. I just ordered 42lb EV14 injectors from them for my FIRST manifold.

GD

 

Good info there. I did the Bosch III units in my C4 6 years ago, and i'm quite sure i did some ECM tuning. Since it is a SD car, i think it is easier to tune than a MAF car. I have an Excel sheet, that takes my datalogged BLMs and modifies the VE table accordingly. Its pretty cool. I am trying to keep my C4 mostly stock, so the tune doesnt need much tweaking. Havent done anything with it in a while. I know they are batch fired, but there are 2 injector drivers, so i think they hit 4 at a time in opposite banks, but i could be wrong. certainly not ideal, as compared to sequential firing. I really enjoy ECM tuning, just dont have the time anymore for test and tune. I have way more time on my Camaro than the C4.

I do understand the Bosch III units a re-conditioned, but they are tested and matched, and i cant hear them firing. The Delphis would be a good choice for a stock R&R, without tuning, copy that. My Camaro is far from stock, have owned the car since '92, and consider it my "test car". I like to experiment with it. Changed many things on it, some things work and some dont. I'm thinking new injectors over this winter, as i want to keep driving it. I thought you could still get new Bosch injectors, seen them for sale somewhere, but whatever.

 

More good stuff here. That injector offset table, has values way under 1.0mS, like 0.275mS or less. Does it really make a difference? As far as my fuel pressure bleeding down, i just followed the flowchart in FSM, first pinched off the supply line, and it still bleeds down, then pinched off the return line, and same bleed-off. Result: replace leaking injectors. My FP regulator has been replaced, but not the fuel pump, so who knows what is going on there. And yes, my original multecs are 31+ years old, time to get rid of them.

I usually hit the key on for a second or less, to prime the rail, then hit the starter. As you know, the FP will only run for 2 seconds, and if no oil pressure will shut off. Not sure what your method has to do with the fuel bleed off. If the fuel is leaking down into the cylinders, after a few hours, you will have long engine cranks. Always starts sooner or later, and giving it a little throttle seems to help it fire.

 

Yes voltage offsets are needed in the off idle area. See: https://www.thirdgen.org/forums/diy-...injectors.html

If you are rapidly loosing pressure regardless of reason, when the pump shuts off after 2 sec. there will be less than needed pressure at the rail. If you start cranking after pump off pressure bleed occurs and it takes a few seconds to either get 4psi oil pressure or get enough DRPs to start the pump. All that time = no start. Crank before 2 sec prime ends and will have more (needed) pressure. Put a gauge on rail and can see it.

 

You could set up a bench test on the injectors to see if they leak down if you really wanted to know for sure. But since I see about 10 posts a month on things that turn out to be leaking or stuck injectors, I think the life span is over for any of the originals.

My car after I did the LS swap was hard to start and I was rapidly (and I mean almost instantly) loosing pressure after shut down. Replaced the fuel pump and bucket (4th gen tank) and solve the issue. I'm 99% it was the check valve but I guess it could of been the integrated regulator.

 

The values at 14.5v are more like 0.650ms to 0.850ms or so. The idle and cruise PW is usually around 2-3ms (with the offset). So yes the voltage offsets make a HUGE difference at idle and cruise. Drop much below the actual open time on that table and watch your BLM and INT rocket up into the lean area (>128).

I just bought some new EV14's for my next engine and they came with published offsets - 14.5v is 0.660ms and these are brand new injectors designed for LS1/LS6 fitment. They are a little faster than the old stuff but not much.

GD

 

Been tuning and using Bosch 3s in these cars since the mid 90s. They work fine.

 

I don't beleive anyone disputes that they work.... with tuning. They are just loud and there are better options with known published offsets. Bosch won't even help with giving out the information - they claim it's proprietary and they "can't release it" - it's a crock is what it is. And they have been discontinued since 2016 so now all you have is reconditioned used injectors out there.

I just bought a set of 42lb EV14's for $380 - flow matched, brand new, and with detailed offsets at any pressure you like. And they came with EV14 to EV1 adapters already installed.

GD

 

I was talking about the other offset table, the injector PW low offset vs base pulse width. From 2.44mS on up, the usec added is Zero!

FYI, i have 793.5us at 12.8 and 549.32us at 14.4 in my other table. Never changed them from day1, after the B3s installed. I will be soon tho!

 

No test bench for me. What i might try, is lift the rail up, with the injectors still connected, and pressurize the system, and see what i can. Might be messy. I did pull a few plugs, but couldnt see any wet ones. Otherwise agree, time for replacements!

 

Ok, understand what you are saying there. What i do, is just a very short pause, from key ON, to key cranking. Way less than 2 secs, i just dont do the engine starting with the key in all one motion, just a short pause in there. Car starts perfect when cold. And yes, i have a mini-FP gage installed permanently on the rail. Just cannot see the gage while cranking, so i will need a helper. A FP gage is the most important tool for working on fuel injected engines, IMO!

Also, i have seen your post, mentioned above, before you even added it here!! Good stuff there, i need to read it over a few times. And i will comment on that one as well.Thanks!

 

That's exactly what I was referring to.

Been there, done that. Assuming pump is holding pressure with your tests, a leaking injector(s) when hot will result in more fuel in the engine than needed to crank. Hot engines don't need nearly the cranking fuel as cold engines. So with the good cold starts you know you're getting proper fuel and pressure. When hot if leaking injectors, you have 2 certain issues and a 3rd possible issue working against you:

1. Excess fuel, compensated for by opening the throttle to get more air, albeit not 85% to get "Clear Flood Mode"
2. Loss of pressure with the leaks, and possibly greater leaks when hot than cold which is not uncommon
3. It's entirely possible that the pump may not be acting the same way when other than cold. Returned fuel heats the fuel in the tank and pump. While the pump may test OK cold, it may not operate or hold pressure the same way when not

I'd bite the bullet and replace the injectors which will likely solve the problem. If not, then the check valve, and if no solution, then the pump. There isn't anything else fuel related!

 

Yup, that is the way i am heading. Just not sure if i want to wait and make it a winter project, or just go after it now. Time is not something i have extra right now, and i still want to drive it for a while. What i really want to do, is try and lift the rail up, all intact, and see if i can find a dripper, with it pressurized. I have had my TPI apart many times, so nothing i cant tackle for sure. On the other hand, i am anxious to figure out this problem.....

 

Update to my issue. This week i proved my injectors were leaking down. Pulled the rail up, all intact, and pressurized. Watched for dripping injectors. Pressure did go down, and the injector tips were wet. Slow drippers, about 7 of 8 injectors. Pinched off both fuel lines, separately, and the issue was still there. Today, installed a set of Bosch III 24lbers, and once it was locked down, pressurized it up. No leaks, and pressure held, like really held tight!
Got the B3s from FIC, and yes, they gave me the battery correction offsets for this model. Values were in 0.5v increments, so i just graphed it and extrapolated the curve, to get some values for my bin table values. Still gotta finish putting it all back togethor, but i will be sleeping well tonight, for sure!

 

Glad you got it fixed. So many problems caused by leaking injectors that many refuse to believe.

 

What offsets did you end up with? I have test data for the 24's

GD

 

Yes, thanks. Worked on it today, but had set backs, so i didnt get it finished. Should have it back togethor tommorrow. I am just really stoked at how the pressure is holding.
Today, when i went back out to shop and work on it, still had like 25psi, nearly 20 hours after i run the pump!
Check out my post in the TPI forum, shows a picture of one of my injectors. I shoulda changed these out 5 years ago!
Mike

 

Here they are, as given from FIC directly:
4.5 7.285745
5 7.169087
5.5 6.218478
6 3.962941
6.5 2.573279
7 1.939834
7.5 1.574168
8 1.309082
8.5 1.114422
9 0.954994
9.5 0.827989
10 0.725101
10.5 0.646214
11 0.573173
11.5 0.500671
12 0.435207
12.5 0.386359
13 0.339858
13.5 0.292894
14 0.24897
14.5 0.212892
15 0.176967
15.5 0.141236
16 0.108773
16.5 0.080887
17 0.054694
17.5 0.029539
18 0.011423

 

These are the Bosch III 24's that are black? If they are the same as the one's I got from Southbay, those offsets aren't going to work. Watch your AFR with a wideband, and unplug the alternator. If the AFR changes considerably when you change the voltage supply then the offsets aren't right.

GD

 

No. These are blue-ish/grey units, 24 lb rebuilds from FIC. They gave me the offsets, so i have to go with them. And yes, they are considerable smaller than what i was using. Does this help?......im sure these are very common replacement injectors......