Greetings! I've been fighting some idle issues (bumpy, occasional miss/hickup) that have not improved no matter how much I mess with it. The problem is actually starting to grow into a miss while lugging up hills and sometimes under slight acceleration. Since everything else is in great health, (all new plugs, wires, cap, rotor, coil, fresh motor, valve seals, head gaskets, timing chain, yadda yadda) I'm beginning to think I may have a clogged injector. The idle has an occasional miss.

The motor is a 87 TPI 5.7, and it's stuffed into a 4300lbs 92 4x4 Chevy truck. I'm running a 730 ECM. It's a 100% stock motor and camshaft with an Edelbrock TES exhaust system piped into a Flowmaster American Thunder cat back system. No other mods, besides a 92 TPI serp belt swap so I could retain my factory truck accessories and locations.

My tune is very close with near 124-128 BLMs across the board and I have my timing tuned good enough to avoid knock counts with medium octane and higher fuel. My idle vacuum reads as about 35KPA. Is this considered a normal idle vacuum? Warm idle iac counts are about 15.

Anyway, I have on hand a nice clean set of 19lb "yellow top" Ford injectors from a 4.6 Lincoln that look clean enough (as far as I can tell by looking into the strainer screens and nozzles) to just drop in.

My question is, since this truck usually never sees much more then 4500 RPM, should it be safe to try the 19lbs? According to the Mustang stuff I read, the 19lb injectors support up to 350hp on the 5.0 cars. Obviously I'd adjust the injector constant and watch my tune closely. From what I read about these Bosch designed injectors, they're quieter then my old 87 Multec injectors (currently annoyingly loud) and are ultimately a better design.

Any suggestions?

 

really sounds like a lean miss. I had the same problems myself. I added 5% to the ve table pretty much across the board at that given rpm where I was having the miss. I think the 19 lbs will make the problem worse. I run 30lbs in my 383 with a mild cam and stock ported alu. vette heads. my numbers were the same at that time also 128 to 133 and 124 to 126 blm. try giving it some fuel aprox 5 to 8 % where you are having the problem. check the rpm and the kpa and change the values up and down one from there. hope it helps.
Joe

 

IIRC, Ford rates their MPFI injectors at 38 PSI. GM rates theirs at 43.5 PSI. The Ford 19 lb/hr injectors running at 43.5 PSI are actually closer to 20lb/hr.

 

It kind of sounds like a lean miss.

I have been running a stock TPI with MAF using 19#/hr injectors in a 350ci truck and rev only to 4500rpm since the year 2000. I have the pressure set to 53 PSI. It has worked fine since then but is starting to lean miss at idle. The injectors had 130K miles on them and now have 200K miles on them.
This is just an example. I can't say if it will work for you.

 

So everyone thinks it's a lean miss? Hmm.

When driving, I can feel the missing only during idle and PE, I think. But sitting still in neutral (it's a 5-speed) if I hold the motor to any RPM, I can still hear a slight breakup. My old TBI setup ran WAY better then this.

Assuming it is a lean miss during PE, since I don't have a WB I'll have to guess. Again, when not in PE my BLMs are about on the money (stock motor, _mostly_ stock AUJP VE tables) the only way I could be _that_ lean enough to cause a miss during idle and cruse non-PE is a bad O2 sensor. I do currently have a 1yr old Bosch 1-wire, but I have a new AFS-74 sitting on the desk waiting for time to install. I don't expect the results to be dramatically different.

Looking at a datalog from my drive home last night (Datamaster v3.5.1), during one PE example (RPM 1225, MAP 99.7, TPS 100%, Speed 46MPH) I see a commanded AFR of 11.7. My O2 volts were hanging around 850mv-950mv. Does that sound right? Or would 850-950 on the O2 indicate a leaner mixture?

Now, as far as the 19lb injectors, I thought it was proved a myth that Ford rated their injectors @ lower pressure? I would think the 19lbs would be fine since my current stock 22lbs normally never go past 40% DC anyway. And wouldn't slightly smaller injectors with a longer PW at idle actually possibly improve idle quality? I never understood why lots of folks love to though huge injectors at there motor when by looking at injector DC, it's usually not needed. I've only been tinkering w/EFI tuning for a few years, so perhaps I'm just wrong here.

I think the next thing I should do is verify fuel pressure. My fuel pressure tester doesn’t have the right fitting for my fuel rail, so I haven’t been able to double check it. I’ve been assuming it’s OK since I have a 1yr old pump and filter. The stock 87 FPR is still there though.

Also, what is a normal vacuum (in KPA) at idle for a stock 5.7 TPI?

 

I think you might be calculating duty cycle wrong (maybe you're forgetting that in batch fire mode, the cylinder gets 2 pulses of the same amount, per intake stroke, or something like that). Max duty cycle occurs near/between peak hp and redline.

Probably not lean miss during PE without it showing up in the O2 (do you see small dips in the O2 voltage?? BTW, high (>450) O2 millivolts is rich, as it's supposed to be when in PE). Check for burnt wires, bad ignition module, pickup coil, heck a fubar TPS can do this too. Get under the hood in completely complete darkness and look for blue flickering under the hood as well. Could be some EFI wire that's burnt or rubbing on something as well.

 

TTS Datamaster calculates and shows injector DC right next to BPW. Full throttle @ 1225 RPM netted about 20% DC & 9.92 BPW. Perhaps TTS is wrong? I’m aware max DC isn’t reached until near readline/high load. That’s why I was wondering if 19lb injectors would be fine in my truck since it never sees redline. It’s a heavy, big tire, low RPM, stump pulling, 4x4 that just cruses to work and back every day. All I want is lots of <4500 RPM torque.

As for leanness in PE, in the same WOT data I posted above, my O2 volts hover between 850-925mv. That sounds too low to me. Shouldn’t 11.7:1 AFR (the AFR my ECM is calling for in PE) show at least 1000mv? I know it’s only a NB sensor, but 11.7 should be off-scale rich?

Since I did the tuned port swap into the truck myself, EVERYTHING has been gone over. If I had a bad TPS, I’d have seen it in my hours and hours of data logs by now. I’ve done the darkness test, the only flashing I see are the plugs themselves glowing. I’ve even swapped in a friends brand new distributor as a test. No change. I’m on my second set of wires trying to clear this problem up too. And an MSD coil.

I started this thread thinking I had a bad injector, never even considering a lean condition in PE since my cruse BLMs are dead on and it’s a stock motor. But after everyone suggested I look there, I did and found what I believe to be low O2 volts during PE.

So, what NB O2 volts should I expect to see during a commanded 11.7:1 AFR PE pull? Greater then 850-925mv?

 

Reading further into NB volts and my 850-930mv range sounds like it may be correct, since apparently that voltage depends on the temperature of the sensor. The AFS-74 gets installed tonight, so I'll know for certain soon enough.

Regardless, it's not lean in PE, that's for sure. So the miss I'm feeling must be something else. I've pretty much ruled out the entire ignition system, so I'm back to the dirty/bad injector being a possible cause.

 

Um, a dirty/bad injector causes a lean miss. I gave you an example of it with the info that I posted. Again, it sounds like you have a lean miss.

I don't pick up lean miss with a NBO2, but can see it with the WBO2.

 

junkcltr: Right on, sorry I skimmed over your 19lb injector part and forgot about it after reading the other posts.

I'm going to get some new injector o-rings and pop those 19lb Ford parts in this weekend if I can find the time. I'll stick with the stock FP for now since I don't have an AFPR and just change the injector constant. Hopefully I don't need to touch the VE table much/at and get by with just tweeking the injector constant.

I'll follow-up and hopefully report a smooth idle and no more lean miss under load after the swap.

 

as far as the kpas I checked a truck 90 gmc van 5.7 and it idled with 35 at 750 rpm. If you look at your ve tables yhou will see that they are higest at peak torque which should be around 3200 for your stock bin(I think). Your lean problem will be worse with the injectors. if it was a lt1 I would say give it a try but being the spider of a intake that it is it would really stink to install the ford injectors and find out what I am saying is true. that is alot of work to have the problem get worse. I guess you could always bump up the fuel pressure to compensate if it turns out to be worse. I have done that in the past to make up for haveing too small of an injector but it will screw with other driving conditions. 870 to 930 is good for wot. I just think you are opening a can of worms with the smaller injectors. 24s would be perfect for your combo. keep me posted I am curious to see what ends up working for you.

 

Try a cylinder drop test. Pull one injector connector at a time, and see if there's one that doesn't make much difference. might want to disconnect the IAC as well, to help prevent it from compensating and making it hard to tell one way or the other.

 

UPDATE!

The 19lb Ford injectors went in Saturday morning. The swap went without a hitch, took maybe 90 minutes start to finish. Since I don’t have an AFPR yet, I just changed the injector constant and reburned my memcal and fired it up. BLMs are still spot on and the idle feels much better. The old 1987 injectors must have been causing the idle problems because it’s almost dead smooth now. However, I still have the same (ever so slight) occasional miss when climbing hills in 4th or 5th gear. The O2 volts are still in the 850mv range, so it’s not leaning out. So I’m still having issue there. I have a spare dizzy from the 92 TBI motor that has a newer pickup design then the old 87 TPI one I’m using now. I’m going to drop in and see if it makes a difference. Guess I’ll have to swap the drive gear since the TBI motor wasn’t roller.

As far as the 19lb injectors keeping up with a 350, at stock 44lbs pressure, if I WOT up to 4500RPM my injectors will go run to 85% DC now, and I can watch the O2 volts drop to the 700mv range. So the 19lbs are indeed too small at stock fuel pressure for a 350. Since I almost never need to drive the truck that way, I’m going to leave them alone for now and try an AFPR soon. For everyday driving, the 19lbs work just fine for now. A DC of 40 seems to be the most they ever see when I drive normally. I like the quieter Bosch disk design II model injectors too. .

I’ll probably get a new set of 24lb Ford injectors eventually. I’m yanking the 5-speed and putting a 700R4 in the truck in a couple weeks and need to save the money to put towards having the trans and transfer case rebuilt before it goes in since it came out of a high mileage truck. We’re taking it down to the Outer Banks in late June for a week to play on the beach and I’d like for my wife to be able to drive it so I can sleep some of the way. Plus I’m tired of shifting the big old 5-speed cast iron NV4500 everyday to and from work. What can I say, I guess I’m a wuss.

 

yeah, clogged injectors mess up the idle. The 19#/hr seem to work good at 53PSI on a 218/218@.050" cammed 350ci w/ TPI that I run. It was cheaper to go AFPR than 24#/hr at the time.

One of GMs biggest mistakes was not putting the TPI 350ci in the trucks. It is the best engine they ever designed for a pick-up truck.

The mis-fire under a load could just be a bad spark plug and/or wire. I would re-check the plugs, boot connections, arcing, etc. before swapping distributors.

 

Well since I have a stock cam, and the extra pressure worked for you, I guess I better order an AFPR today.

This afternoon I'll spend some time looking around for wire that might have rubbed through. I changed the wires and plugs, cap and rotor, and swapped in an MSD coil chasing the miss just a few months ago and no change.

Maybe it's time to go take my spare 4-bolt main high nickel roller truck block to the machine shop and order a 383 kit.

 

Hang on a sec....

You see the plugs glowing? Better describe this a bit more, I've never seen spark plugs "glow", even after dark....

 

I should have described it as flashing. The porcelain flashes with the combustion in the cylinder. If it's idling away, and it's totally dark outside with all the lights out, you can see every plug flashing away. It's pretty cool. LOL

Don't tell me I'm the only one who has seen this?

 

UH, I've never seen anything like that, maybe I've not looked close enough? Or maybe you've got a plug or ignition problem? What kind of plugs are you using? If you tell me they are the Accel's (or any other brand with the screw on top piece), I'm gonna tell you to pull some plug wires and see it any of those stupid screw on ends has come loose like they ALWAYS have any time I tried using the Accel shorty header plugs....

 

All my Chevy v8s have done it. My fatty cammed 11:1 355 powered 1968 C10 truck, a 454 in my 78 K10 truck, the old stock TBI 350 in my current truck, and this current TPI motor.

I'm running AD-Delco R43TS plugs. This is correct for a stock TPI 5.7, right?

BTW: AC-Delcos are the only plugs I use.

 

Guess I'll have to try checking that out. Never seen that. Either that, or.... You aren't related to Clark Kent are you?

 

like I said they arfe really too small for your engine and I still think it is a lean miss you are feeling rather than a ignition problem. You use more fuel at peak torque than at peak hp on that stock motor so if you are coming up lean at wot you are really lean at peak torque. try bumping up your tables 5% where you miss occurs. I have 3 or 4 sets of used low miles 24lbs lt1 take outs laying around. If you want to cover the shipping you can have a set. no point in continuing to patch the problem. I guess I should have offered it up before the change but I thought I (and others) would talk you out of putting in the smaller injector. pm me if you want them.
Joe

 

lt1z350:

Actually I think the miss is gone. The hill I climb on the way home from work every day is not the smoothest and I think I may have just been feeling that. I took the truck on a 45 minute drive each way tonight as a long test drive to log some data and visit some family, which is quite hilly and I didn't feel a thing, even really lugging it in 5th gear. Sorry for dragging this on longer then it needed to be!!

Anyway, the injectors just BARELY touch 85% DC by the time I hit 4700RPM. Under 4500 RPM, they're still OK.

As for the VE adjustments, since my problems only seemed to turn up in PE mode (even at 1800-2500 RPM where the smaller injectors are still PLENTY large enough) and I had no lean missing out of PE, I don't see how increasing VE could help. I could adjust those areas of the VE table, but my ECM would just lean them out when I touch them outside of PE mode anyway.

I think my miss was caused by a clogged injector. Under cruse I couldn't tell, but as soon as the motor was lugged enough, one cylinder was starving for fuel and would miss. Now with the nice clean Ford injectors, I'm getting more consistant fuel to every cylinder and the miss seems to have cleared up.

Unless I'm completely missunderstanding this stuff. I'm still kinda new at it.

Thanks for the injector offer! Actually I have a set of 24lbs from a 94 LT1 caprice I was going to use. But I've read plenty about the old Rochester Multec design injectors going bad after sitting because of a poor coil insulating design. It seems any moisture sitting in them causes the coil to corrode and break down. Since mine appeared to have been sitting in a junk yard for a while, I decided not to use them. I was going to send them to Cruzin Performance for cleaning but he suggest I just get a better set of injectors to start with rather then risk the cleaning service fee just to find they were too old and no good. I'd rather have slightly smaller injectors that are more reliable then a set larger injectors that were no better then my old 1987 ones. What year are your injectors? If they're not Multecs (two-tone body that looks sorta like a pill with a big shower head nozzle) I may take you up on your offer!

 

I've never not seen it.. be it autolite, or ac-delco, whatever.

 

OK, I stand corrected. Just seems strange that I've never noticed that before. Will have to try and see that tonight or tomorrow night....

 

Never seen a spark plug light up on a good ignition system. I knew of a Suzuki 2-stroke 125cc that used to make the NGK plug light up blueish color at night. It also fouled plugs after about 1-2 hours of ride time. This was due to a bad coil/ignition system.

 

I have seen this on brand new plugs in the 454 in my 77 C10(it was in a really dark spot out in the woods). It is completely normal. That is a lot of fire behind those plugs. Only seems to be AC Delco plugs I have noticed, but then again I never had anything without them

 

All of my plugs flash too! Good to see which cylinder is not firing when you've got a miss at an idle

lt1z350: I've got 19 lb/hr Ford injectors in my mildly cammed 355 as well. If you'd be willing to extend the same offer to me, I'd love to get a set of 24 lb/hr injectors for my 3/4 ton 4x4 truck before I start getting it all tuned up on the 19 lb/hr injectors