C-lab

This is going to be a ridiculously long post, but I want to clearly state the problem and what I've done so far to try and fix it so y'all can help me as good as possible. I've read thirdgen off and on for awhile now and this is the first time I've started a thread because most problems can be answered with a google search but that hasn't worked for this one yet.

A couple years ago I swapped in a TBI 350/4L60E combo out of a 93 Suburban into my 76 K5 Blazer. It was my first fuel injected swap into an older chassis like this but it was pretty straight forward and I was a tech at the local Chevy dealer at the time. After I put the setup in, I thinned out the wiring harness of all the stuff i didn't need and soldered everything in place with the harness routed how I wanted. I can't remember exactly when the problem first started, but sometime right after I swapped it I developed a long crank especially when cold. I also developed a drive ability issue where with the throttle barely open the engine ran like total crap. Also it began to stall out occasionally. It's been this way for a couple years now and I'm embarrassed to say that it still has all of these exact problems and I haven't figured them out yet.

What I do know after a bunch of testing is that I don't have any injector pulse until I have oil pressure. I've verified this with a noid light and with the oil pressure sender/switched unhooked I get no injector pulse, thus it won't run. My fuel pump relay is good, the pump runs and I have good fuel pressure (I checked it with a gauge multiple times before I figured out for sure it was no injector pulse, not a pressure problem), and the valve that keeps the fuel from running back in the tank is good (I checked this while I had the pump out making sure the hose that I put in between the pump and sending unit was still in good shape and attached securely). I have spark without the oil pressure switch, but no injector pulse. I just bought a used PCM off of eBay to rule that question out and I will install that this weekend as a test. I'm guessing that I screwed up something in the harness when I thinned it down but I'm not sure if that's really what's going on or what exactly I screwed up with it. I have the factory GM wiring schematic for a 95 model but they aren't identical and I'm not sure what I'm looking for exactly.

Is it for sure supposed to run without the oil pressure switch hooked up as long as the fuel pump relay is good? I have checked my brother's 88 TBI K5 and it runs without it but I'm not 100% mine is supposed to be the same way. What should I look for as a connection between the oil pressure switch and injector pulse? Could this long crank be related to my other drive ability symptoms? I've checked the wiring between the pick up coil and PCM with a multimeter and all of the wiring is good. I've also replaced the entire distributor with a junkyard unit because I bent mine while swapping the trans out. I also have installed a new GM ignition module because that broke along with the dizzy.

I'm an OTR truck driver and won't be able to work on it till this weekend but I really want to fix it so I figured I would post up here and see what help I could get. Give me anything I should look for when I'm trying to diagnose it this weekend and ask any questions about stuff I left out.

Thanks in advance. I hope someone knows what I've got going on because this is one weird problem and I have no idea what I screwed up.

-Caleb

Ron U.S.M.C.

This is kind of interesting = http://autorepair.about.com/library/a/1/bl526.htm

C-lab

Thanks for trying to help but the only part that mentioned injector pulse was talking about Chrysler and I'm not working on a Chrysler. I'm working on GM and the only thing it discussed about GM was fuel pump related which I've already ruled out because I originally thought it was my problem. I'm trying to figure out the connection between the oil pressure switch and injector pulse, and whatever I either screwed up in the swap, or which part is faulty and causing my problem.

Thanks, and please keep the info coming. I'm hoping one of you TBI gurus will know what I've got going on.

Schurkey

Misread original post.

C-lab

I've tried to be clear but maybe I have not. The fuel pump primes exactly as it should. The fuel pump has good pressure. I tried it multiple times with different gauges before I found the real problem- no injector pulse. I have great fuel pressure but the injectors won't pulse until the engine builds oil pressure. If I disconnect the oil pressure switch the injectors never start to pulse and thus it won't run. I'm testing this with a noid light. I have spark with or without the pressure switch hooked up, but no injector pulse unless it is hooked up.

Bottom line: fuel pump and fuel pressure good but no signal to the injectors getting them to fire without oil pressure. I don't think this is normal operation and want to get it fixed.

Schurkey

Do you have power to the injectors before building oil pressure? Since the ECM fires the injectors by supplying ground, the injectors should be powered with the key on, engine off.

jokerZ71

Is the wiring harness,ecm,& all from the same vehicle?Had this exact same problem in an S10 swap.Installing a 2000 engine & components into a 99 S10.We swapped engine,fuel system,wiring harness'everything into the 99.All plugs plugged up.All wire color matched,but,injectors would not pulse.Even tho everything plugged up & matched,the same wires from 99 to 2000 had different functions.We ended up having to swap fuel rails,injectors,& everything else back to the 99 components & harness.

C-lab

I don't know the answer because I hadn't thought to check and see which was missing yet-power or ground. This is the first thing I will check this weekend and will report back. I should be able to check and report back by Friday.

C-lab

Everything came from the same year so I'm thinking I hooked up something wrong in the wiring. Thanks for sharing though, it's good to hear someone else has had this problem and overcome it! Haha, I know that it's fixable just like any other problem but this one has plagued me for awhile now and I was starting to feel like I'd never get it fixed. I'm feeling more confident now though.

Thanks for the help guys.

morgsie

iTrader: (1)

My guess is you don't have a "HOT WHILE CRANKING" wired to the ECU. You most likely have IGN voltage wired to it, which means when the key is in the "crank" position no voltage is supplied. Get a wiring diagram and a voltmeter, you missed something when doing your swap.

one92rs

iTrader: (5)

longer cranking times when cold is nature of the beast with the tbi engine. check the CRK fuse to make sure it is getting power during cranking. mine will take a few turn overs when cold to crank. when it is warm it starts a lot quicker. how does it crank when hot? if it is still long then there is an issue. what is the fuel pressure when the key is on for three seconds? what is the fuel pressure when running?

as for the tip in bog search for just that.

C-lab

This sounds very likely. Thanks for the insight.

C-lab

It cranks up fast when hot. But I always have to press the throttle once I hear it start to hit for it to fire up, hot or cold. Can't remember what the fuel psi was off the top of my head but both were in the 9-14 range when I checked them last. I will check the CRK fuse. I don't actually have the TBI fuse box, but I'll check the fuse where that wire is run to. It takes mine longer than any TBI I've heard to fire up cold. I spin it over until the SES light goes off, then turn the key off and try again. On the second try the oil PSI jumps up, I hear it try to hit, stab the throttle and it fires up. If I keep spinning on the first try with the SES light off it will never fire up. I'm not sure if that's normal or not.

RBob

iTrader: (1)

I'm with morgsie on this one. The accessories terminal on the ignition switch goes cold during cranking. This is why the radio will turn off then. Need a tap that is hot during both key-on and cranking. Do this for the ECM IGN power, coil/distributor power, and the injector power.

The reason the second attempt gets it started, is that at the end of the first crank attempt the injectors spritz a little fuel in.

I used this to my advantage many moons ago, on a carb engine with a points distributor. There was so much initial advance that it wouldn't hot crank (it kicked back). So I moved the coil power feed to an accessory position in the fuse block.

I'd crank the engine and it would catch and run once I let off the key.

RBob.

C-lab

Update: I put in the used computer and it seems to have fixed the long crank. I thought for sure I had the wiring wrong but maybe I'm vindicated. It will crank up and run without the oil pressure switch plugged up now.

I also installed an AC Delco EP381 fuel pump that is recommended by Brian Harris from TBI Chips. It's a stock Vortec 350 but he recommends this pump for both TBI and TPI upgrades. I'm swapping to TPI later on so this was part of that eventual upgrade. The fueling needed to be adjusted in the chip of course, so my brother burned me a new tune. When I put it in with the moates equipment, my long crank was back immediately. The chip turned out to be a dud and put me in limp home mode. I haven't figured this part out yet and will keep you posted. Thanks again for the help.

C-lab

Another update: I put a good chip in the new PCM with the moates adapter and its running good but the long crank is back. I'm confused at this point. I'm glad that my drive ability concern is gone but now I need to get the long crank fixed. When I worked on the truck last weekend I spent most of the time on the pump. Then when it seemed that the new PCM fixed the long crank, I didn't check out my wiring to see if it was in fact that I ran something to an accessory wire that isn't hot while cranking. I could've easily done that.

I won't be able to check this for two more weeks at least but I will check at some point. When I figure it out I will post the answer here. Thanks for all of the help so far.

C-lab

Ok, so it took me forever to look at my wiring to the fuse block. I finally did it and y'all were right. Thank you to morgsie RBob and others. I had 4 wires going to blade terminals under the dash. 2 of them stayed hot while cranking, 2 did not. Now all 4 are hooked to the 2 that stay hot while cranking and it fires right up (as fast as any TBI at least) with no throttle input. I still have a drive ability issue under light throttle that I need to diagnose but I'm happy for now.

The reason it took me so long to look at this is because I have an LT1 sitting in my shop that I planned on putting in my S10 but I think I'm going to stick that in the K5 and if I wire everything correctly my drive ability issues should be fixed.

Thanks again for the help. Sorry it took me so long to follow through on the direction you gave me.

Cam_RS

I have a 91 camaro TBI, it doesnt have power on injector connectors and no ground on ecm while car is on. Any idea whats wrong with it?

C-lab

I would check the injector A and B fuses. I'm not the expert though. If the experts don't check in on this thread post up your own thread with the question.