KDMatt

Hello, I've been lurking on the forums for a while to soak up info about my Crossfire EFI system, (there've been some really informative threads here!) but I've run into an impasse and could use some insight.

The backstory on my situation:

I'm the owner of an '82 Trans Am that came with Crossfire EFI. When I first bought the car I spent about a month learning what I could about the Crossfire system, checking/adjusting all of the sensors, replacing the IACV's and eventually had it dialed in and running smoothly. I haven't driven the car in almost 3 years after the original 305 overheated and lost compression.

Last year I rebuilt a 350 to go into it, but decided to keep the Crossfire EFI since I'd had such good luck with it previously (lol.) So I grabbed the corvette injectors and another crossfire intake (for good measure) and put it all together.

I'm the 2nd owner of the car, and it only has about 54k original miles. I elected to keep the Crossfire system to keep the car looking/running as original as possible. I thought the 350 would be a good way of increasing the performance of the car without making it outwardly too obvious that it had been modified.

The third-gen community seems to be a pretty mixed bag on Crossfire knowledge, and given that I'm now using a 350, it made sense to me to reach out to the Corvette folks, which is why I'm here.


The current problem:

I'm getting intermittent spray from the injectors during cranking. I confirmed that this is an electrical issue by attaching noid lights to the injector connectors, and the bulb is only blinking periodically, and dimly. (I can take a video of this if this description isn't enough.)

I have the 1982 Factory Service Manual, but the diagrams and references are really tough for me to follow... also my exact problem is absent (Intermittent/Weak spray.)

I spent a little time digging and thought I'd found the problem - The HEI reference pin for the ECU was reading full battery voltage during cranking, which allegedly meant that the HEI unit was faulty. I replaced that (and the coil for good measure), and didn't see any improvement in symptoms.

I'm still getting intermittent, weak spray, and it's definitely (as far as I can tell) a voltage issue at the injectors. I also don't get any spray just from turning the key to the "on" position (which is something I understand is supposed to happen) What am I missing? Is my ECU dying?

Thanks in advance for any advice.

84 4+3

Iirc you do not get spray at key on. You do get the fuel pump cycle. Check the injector signal at the ecm if you can find the pins in the fsm. That'll tell you if it is simply a wiring issue. Also how does the tach behave? I don't remember if the pulses reference the pickup coil but it could be on it's way out as well.

ex-x-fire

Check the fuel pressure.

billschroeder5842

Start there. I had a 82 C3 with the XFire. Lots of XFire problems can be solved with good fuel pressure.

You should have a minimum of 11. If you have any less you need a new pump (get a 85 to 89 vette pump as it will give you +15) and swap the fuel filter.

KDMatt

Thank you for the quick replies and the sage insight.

@ex-x-fire Checking fuel pressure was next on my list, I just have to finish building/inventing the T-fitting that goes between the TBI's so that I can hook up one of my gauges. I'll see if I can't get to that today or tomorrow.

I do still suspect that it's an electrical problem, since the noid light for the injectors blinks so dimly and intermittently.

@84 4+3 Can you tell me more about what you mean with regards to the tach? Are you suggesting that a bad pickup coil might be sending bad reference pulses to the ECU or something like that? I think it's a plausible theory. I'd have to sit with the schematics and really figure out which circuits are responsible for triggering the pulses.

Also @bill I know a lot of vette guys have upgraded their fuel pumps to the 85's and later C4 ones... and I also know that GM made a LOT of interchangeable pumps, but would a later 'vette pump work on my T/A? Also, in case you're not familiar, changing a third-gen f-body fuel pump is not for the feint of heart haha.

Thanks again everyone, I'll see what else I can find.

corvettenorway

you can use later type fuel pump .

C5 Diag

KDMatt

Holy cow!! Is that ERIC THE CAR GUY? (Edit: No it's not but it sure looks like him at first glance)


I just wanted to report back that I tested fuel pressure between the TBI's and have a solid 10 to 12 PSI, i.e. it hits 10 psi with Key on, and reaches 12 while cranking. Fuel pressure isn't my issue it would seem, confirming my early diagnosis that it's electrical.

Can you elaborate on this a bit please? This sounds super useful.

Thanks again!!

84 4+3

I believe that is just a regular test light/probe.

KDMatt

I'm re-reading, and I think what he's getting at (if I'm not mistaken) is checking for 12 volts at the injector harnesses with the key on.

Seems simple enough. I'll go try it.

KDMatt

I've got 12 volts at each injector.

I've checked all of my grounds, and I've got maybe only 1.5 to .9 ohms of resistance to any given point I check, so I don't think it's a grounding issue.

The thing sounds so close to wanting to fire. If I let it sit for a few hours I'll get a fire on the first crank, but it'll die almost immediately after that.

I'm going to keep looking at my circuit diagrams to see if there's anything else that pops out at me.

EDIT:

I've got continuity so far from the EST/Spark circuit to the ECU

I also spent a bunch of time checking the coolant temp sensor circuit, since when I probed the connector it showed no continuity/open. According to my FSM this isn't right... The coolant temp sensor shares a ground with the TPS and MAP. I traced the circuit all the way around. The connector from the Coolant temp sensor to the ECU (yellow) is good. The ground connector from the CTS to the TPS is good, and from the TPS to MAP and ECU is also good.


Given all of that checks out, I then decided to check the TPS itself... This is where it gets a little interesting...

The FSM says to probe ports B & C on the TPS harness, and that the voltage with the key-on in the ignition should read .525 volts, give or take .75.

The voltage I'm getting is well over 4 volts, oscillating a bit as I move the sensor up and down, but still in the neighborhood of 4.3 to 4.6 volts, depending on where I situate the sensor. Would that mean that my TPS failed? Could this be my smoking gun?

I'm not sure how the TPS really works, but I'm wondering if something inside of it has potentially broken the circuit through it to the CTS.

C5 Diag

jseremba

Is the oil pressure switch working. Remember the car has a sensor. If it has less that 10 psi it will not run. The car should run for 2 seconds and then the ECM should kick in. Just my two cents. I hope it helps.

84 4+3

is B and C the top two wires? If so it could be foobar. Iirc around 4 volts it registers as wide open and I believe that is clear flood. At least on newer gms... basically meaning it won't fire off.

KDMatt

Good morning! Thanks for the replies!

@rwobs777 I understood later what you meant. I checked the voltage at the injectors and had 12 volts. Also checked fuel pressure, which is between 10 and 12 PSI, and on a Crossfire EFI system that's well within spec (9 to 13.) I said on my noid light that all was NOT good. That the pulses I'm getting from the ECU are very weak and intermittent.

I also watched all of the videos you linked. Holy heck that guy is thorough. Great series!!

@jseremba Thank you for the suggestion! Is there a "quick and dirty" way to check the oil switch? I'm not convinced it's playing a role in my problem (yet) but I'm trying to remain open to every possibility.

@84 4+3 Yes, B and C are the two top wires. It's not so much that I'm concerned about it sending a WOT signal/flood - it's that I believe the continuity is broken within the TPS itself -- and without that continuity the CTS doesn't get a ground, hence the circuit reads open.

I'm not positive how the Crossfire system registers engine temperature, but is it possible that with the CTS wiring running as an open/broken circuit, and with the TPS as an open/broken circuit, the thing is just leaning itself out into oblivion? Hence why I'm getting such tiny tiny pulses from the injectors?

Frankly, this doesn't seem right to me on paper... but I'm willing to try a new TPS. The blessing of these things is that theses sorts of parts aren't too expensive or hard to find, lol.

The only other EFI system I've troubleshot this extensively is the Bosch L-Jetronic on my 280z, and when a sensor or circuit fails in that car it almost inevitably ends up going pig rich.

Any other thoughts on the TPS? GM's EFI is pretty new to me overall.

Ahnenerbe

You could be on to something with the TPS, I would buy a new one and set it properly.

64Scout

The oil pressure switch is a redundant backup to the fuel pump relay. You could jumper those two to get your fuel pump to run non-stop.

The TPS... I converted an International Harvester motor to tbi, and had the wrong connector for the tps. It still started ok, but would lean out when you revved it fast. I would try unplugging it for a test.

One other thing, a timing light makes it real easy to see the injector spray.

KDMatt

Ah ok, so the oil-pressure switch is just a backup for the fuel pump? Then I've already effectively "tested" that then. I tried cranking the car with the fuel pump connection jumped so that it would run constantly and my symptoms stayed the same.

I hadn't considered unplugging the TPS altogether. Not sure what would happen if I did that, given that it might already just be an open circuit at the moment. Good suggestion all the same.

I'd shine a light on my injectors if there WERE any spray. Right now what I'm getting is super super minimal. I remember being able to see them spray with the naked eye before.

Hot Rod Roy

Per '84 FSM: "If the TPS is sticking or binding in the wide open throttle position, the ECM will be in the 'clear flood' mode. The air/fuel ratio will be 18-20:1, and this may be too lean to start a cold engine."

"Caution: Do not apply a continuous 12 v. to the injector terminals. The injector coil will be destroyed in 5 sec."

Normal spray pattern (viewed with strobe light):

KDMatt

Oh, "CLEAR FLOOD"

Well shucks that makes a whole heap of sense then. You're saying it's acting like it think it's flooded and deliberately leaning out like crazy to compensate.

Also, caution appreciated, but don't worry I'm not applying 12 volts to the injectors - I was just checking continuity on the positive leads.