I have an 85 350 tpi. Seems to be original. Starts right up, but runs very rough. Smokes black and will smoke you out of garage in less than a minute. car was sitting for years and I purchased from someone who already replaced the fuel cell and fuel pump. I took it to a garage to have it checked on an obd1 and the readings were varied. Fuel pressure was good at 40 something psi. Suspect TPS: replaced, no difference. Intake manifold temp read 370 degrees. Also o2 sensor was flat line, but the problem exists long before warm up. Got car back checked plugs out all 8 were wet. Oil smells like gas. Removed plenum and fuel rails with injectors assuming there may b a leak. Pressurized system with key on. No leaks. Removed 9th injector (someone said it may have been leaking). Ohm tested all injectors 16.4/5 All of them. Ready to put it back together, but believe problem will persist. Any advice/ suggestions would be appreciated

I would bet your primary injectors are shot. They more then likely lacquered up and that was that... Toss in the fact that they are 25 years old... yea...

Do this, before reassembly, remove the injectors and rails from the intake, leaving the injectors in the intake.

You may want help, or, a couple of strips of cardboard, but the idea is to watch the fuel spray pattern during startup.

Lay the cardboard under the tips of the injectors and then turn on the key, trying to start the car. Whilst starting, hold the rail above the cardboard. See where a helper comes in handy?

I would unplug the coil, you don't want spark around this process!

Watch for fuel pouring out, or, fuel coming out in trickles versus neat sprays. Then shut off and see which are still leaking.

Make sure the intake manifold is solid, too. If it has a large vacuum leak, the system will compensate by overloading fuel.

Also, the ohms are reading high, IIRC, they should be below 15 ohms.

If the above tests prove my theory out, you will want to get new injectors. FIC/Corvette Injectors, is the best place to go. They will get you the EXACTLY the best fitment and at the best price. www.corvetteinjectors.com - yes, they are a sponsor of the Guru, but I try to only cherry pick the best vendors with the best customer service.

I'm thinking possibly injectors or coolant temp sensor.

Ohm check on injectors only tells you if the coil is damaged. But they can still easily leak or be damaged and flow way too much under pressure. As andy said, you can check that by lifting rail and getting some paper (try blue shop paper towels) under the tips. Key on to pressurize system, to repeat, turn key off for ~10 seconds and back on. You will probably have to loosen the a/c compressor bracket in order to allow enough movement on the fuel lines to lift the fuel rail. Doing that requires removing the belt tensioner, and after you have the water pump bolts out, there's a hidden bolt just under the compressor pulley that requires an open end wrench or a torx (T30?) to loosen. You DO NOT have to remove the a/c clutch or the valve cover to loosen the a/c bracket+compressor to move it forward.

I've also installed the drivers side of the fuel rail upside down and cranked the engine (with distributor power (pink wire) unplugged or fuse pulled) to check the injector spray pattern for any obvious damaged or blocked injectors. yes the injectors will point up and spray into the air.

With that said, I've been told the 85 injectors (24 lb/hr) are pretty good units and worth getting rebuilt. Or for not much more you can get a brand new set, ~$200. Ford/Bosch blue tops are rated at 24 lb I believe.

I also mentioned the coolant temp sensor (CTS). This is on the front of the intake base. The CTS feeds the ecm and has a huge effect on how it runs. This does NOT feed the dash guage. There's a chart in the GM service manual that shows you how to measure the ohms and compare it to the dash guage temp.

Andy, I don't think it's possible to check injector spray pattern without flipping one side of the fuel rail upside down. the method you mentioned is really only good enough to pressurize the rail to look for weeping injectors. You simply can't get the fuel rail high enough with how the fuel lines are routed on the 85. I would not bother cranking the engine during this test.

I'd start with the coolant temp sensor. That sends a signal to ecm to enrich the fuel amount during cold starts, and a bad cts causes all kinds of problems.

Also, if the O2 sensor is bad, you need to replace that as well. If it senses a lean condition, it will add fuel.

One more question, did you pull any codes?

Matthew

Thanks, I was not sure about trying to start it. The fuel lines are too short to lift the fuel rails high enough to do this. ,However I did try two things. First, I bench tested the fuel rails with air pressure blocking off the return line with 50 lbs of air and nothing leaked. Next I connected the rails back the lines and put paper towels underneath the injectors and turned the key on on to pressurise the system. Also only the ninth injector block off plug leaked, but I already knew that and will replace. However, I know this is not my problem. I can disconnect coil and turn over, but was worried about shit falling in the injector/ intake ports, but I can get around that. I will try that tomorrow. I don't mind changing out the injectors, but would hate to do that if they are not the problem. Someone else mentioned coolant sensor. I there any way to check it? I will see if the mechanic I took the car to saved the codes, but I'm not too sure about what he knows. He told me he had a similar problem with a TPI before and never could fix it.

I was told that the o2 sensor has no effect until the computer goes into a closed loop or until the engine warms up.I may be wrong, but this is what I was told. Can the coolant sensor be checked somehow?

Welcome aboard. Where are you located? The codes are easy to pull on an 85. short pin A and B I believe. Read the codes on the drivers information panel in the center of the dash. The check engine lite I believe. Another good purchase would be a factory service manual.

I'm in south west Michigan. Also have a red 4+3 85. I planned on getting a book soon. The only vette I have and the only TPI so all this is new to me. Carbureted engines, no problem, but this is an entirely different animal to me. Please fill me in on gathering the codes if you don't mind.

Quote:

Right, O2 sensor is used once the car goes into closed loop. Factors for closed loop according to FSM are over 400 rpm, coolant temp sensor over a certain degree, and O2 sensor has warmed up enough to give readings.

So you can ask yourself, when is my car going in to closed loop? And you can't answer that - you need to datalog somehow. If your CTS is bad I think it could send the car into closed loop too soon.

You can test the coolant temp sensor by pulling the pigtail off and using a DVOM to check the resistance of the sensor itself. There is a chart of values in the FSM, but I don't have it in front of me. I'll check it later.

Matthew

Quote:
I'm not sure how you attained/read this value, but this is suspect. It sounds like intake temp (Manifold Air Temp.) not coolant temp. that you are reading. I would start there by checking if it set the code for mat sensor.

Good eye, Mick! I totally missed that detail... reread it and duh...

I have an 85 4+3. It was running super rich to the point of barely idling and smoking thick black smoke. Not drivable. Before I messed with it I pulled these codes. 12, 22, 33, 43, 45. After resetting the battery replacing the fuel press reg wit adjustable one, replacing the plugs and wires, CTS, MAF, 9th Injector sensor and putting everything back together. I started it and it ran exactly the same, Exactly. While running I disconnected the MAF and it ran a little better, cut way down on the smoke, but still missed. I also disconnected the TPS and it ran about the same. The injectors were tested under pressure , FP is 42lbs and did not leak. Injectors all ohmed out at about 16 Ohms. The new codes are 12, 22 and 33. I replaced the tps and set it to 5.4 volts. I really don't know what else to check nor how to proceed. Please help

raimunelar -

I merged this in with your original post. This is a continuation of the same problem, so it's best to keep it together.

I would say your MAF is bad, if it made a change.

If it is still missing, it could be fouled plugs, or a bad cap/rotor. I would inspect the cap/rotor before going to much farther.

33 is a MAF code, 22 is a TPS code.

You can buy a reman MAF from autozone and try it out. If it has no effect return it. They do returns generally speaking if the product is still sellable. Ask the clerk beforehand though.

Thanks, I will check the cap and rotor, but I suspect it is not the MAf. I have 2 of them. When I plug either in the problem is the same. Don't 85's have a burn off unit that is supposed to burn crud off the maf on cold starts? I Don't think there is a code for that. Already replaced the TPS and set voltage to .54 v. I will buy another maf if I can return it, but doubt that will rectify the problem. Another issue is that the cooling fan goes on when I jump the A/B plug to get codes. Is this normal?

I defer to Central Coaster, he is much more familier with the behaviour of the early L98 than I am.

However, if you are getting a code... well, where there is smoke... I would chase that harness back. I had an issue with my wifes 87 where the wiring at the weatherpack was so bunged up that it was causing deadshorts.

Also, are you sure that both MAF's are good? Just say'n...

I'd run some scans via an ALDL cable and laptop. That will tell you what your coolant temp sensor is sending to the computer.

Yes it's normal for the fan to come on in diagnostic mode.

And yeah, a code for the maf circuit could mean any number of things, including the burn off module. And never assume a replacement part is good. The first replacement maf I bought was defective out of the box.

Regarding the coolant sensor:

210F = 185 ohm
160F = 450 ohm
100F = 1.8kohm
70F = 3.4k ohm
40F = 7.5k ohm
20F = 13.5k ohm
0F = 25k ohm
-40F = 100.7k ohm

Quote:

Do the MAF diagnostics
http://www.batee.com/corvette/codes/index.htm

Ok, Paid for and ordered a new MAF
fromk Advance Auto, they will take it back ( AS LONG AS i DO NOT INSTALL IT) hmmm.. Pulled the dash top and saw that the burn off module wiring has been poked and prodded at to test for voltages. Car starts and runs much better without either maf hooked up. As soon as I try either one, I get smoked out. Brown wire from Burn off module under dash was cut and disconnected. I reconnected and swapped the module with another just to see what would happen. No difference. I swapped ECM with another ( exact same one) No difference. Still the same. I noticed that knock sensor has no wire or plug going to it? This is important, No? There are two cut wires in the vicinity , but no plug, One black, one blue.. Any idea which one should go to sensor? Also need the right type of plug now as well. Back to the junk yard tomorrow. Thanks for all the help so far from everyone, I have been learning a lot, but I still prefer carburated engines.

Ok... You really need to get a copy of the Helm Factory Service Manual.

You are getting in over your head without it. It will have all the wiring diagrams you will need.

It is obvious that the harness is buggered up, no question about it and you will need to resolve it. Sure, we can help. but for us to help you, you must help yourself. In this case, that means buying the service manual.

The harnesses for the pre-1990 Corvette are junk, at best. They wear, chaffe, crack, shrink... you name it, they do it... and you may be in for a major rewiring.

Off the top of my head, a disconnected knock sensor won't cause this, but it will cause other performance issues. Cold and at idle, it shouldn't do this.

Get the manual, you will thank me later.

Thanks, I am waiting for a factory service manual which I purchased. I am continuing with diagnostics though. A senior guru sent me a link with MAf schematics, but they are for 86 on up using burn off relays. I would like to see one for 85 which would use the module. I do not have any voltage in the purple wire to the maf and wanted to know if there a was a fusible link for that?I don't mind doing all this because it simply makes me understand the system better. I believe the plug for the knock sensor is thee, but is melted. I would need to find another and slice it in. Before I purchased and entire harness, I would like to find my problem.
Thanks again

The entire harness isn't as easy as it sounds.

Much of the engine harness goes into the dash, without the benefit of a connector. So you have a bunch of wires going all over the place. Ick-poo, trust me.

I don't see you getting any farther until the book arrives.

Well, finally got a service manual and followed the procedures to the T. However first problem is first. With everything connected the car starts and runs so rich it will barely stay running. I try to keep it running for several minutes so the check engine light would come on, but it never does. The oil pressure gauge shows a constant 80lbs and 40lbs before I even start it. After shutting off the only code it throws is a 12 and sometimes a 45. I already know this. With the maf sensor ( I now have 3) disconnected the car starts and does not smoke, runs a little rough but not that bad. while running and in diag mode engine light flashes quickly. I presume open loop. Of course after I shut it off it throws a code 33, not surprisingly since the MAF is disconnected.. Today it threw a 13 for the O2 sensor. Its like all over the road. I will post this and go back out and continue diags, but am getting pretty frustrated at this point. The service manual has not really helped me much at this point.

checked for 12 volts at burn off module connections A and B. A was Ok, B: nothing. Wire looks purple /blk stripe crk 39, but book says its pnk/bl. runs to ignition and egr? should have 12 volts when key is on. any ideas anyone? Also have two relays right next to wiper tranny. all wires look burnt and badly frayed on one. Are these fuel pump relays at that location?

You are running into the problem of all problems with early C4s. The wiring harness is garbage.

The wires will crack, shrink, short, break, chaffe... you name it.

The next step is to start isolating potential problems with the harness. You will need to use the service manual and start toning out various circuits.

Take the time to learn the manuals a bit, too. Don't be impatient with this process. Take your time, one circuit at a time and fix it and move to the next. The payoff will be a good running car at the end, it just may take some time to get there.

Review the schematics; review the troubleshooting.

Start with the schematic and using as many different coloured highlighters as you can find, trace the wires you are first concerned with. I would consider getting several copies made of the schematic pages so you can isolate circuits.

I must reinforce this reality: THERE MAY BE NO EASY FIX!!! It will require a step-by-step, methodical approach to this. A guess won't do it.

When these harnesses fail, you can easily get the case of ground "A" shorting out circuit "2", circuit "1", which uses ground "A" could throw the code.

Also be ready to replace the various bad connector ends. GM and Rock Auto both sell them at reasonable prices. Unfortunetly, there isn't an aftermarket source for a new harness...and you wouldn't want to do that. The engine harness goes into the firewall and integrates with the IP harness. This means there is no quick disconnect between the two. Pin by pin... and the disassembly of the dash.

Thanks, I finally got it, but it took hours and hours.. and it was wiring issues.For now it is running fantastically well.