I have installed a 1990 350 and 700R4 in place of a 4.3 and 200 metric. I am using the computer from the 1990 350 but the car is not running very well. It idles great but when you get on it, it just dies out. I'm thinking it may be the computer. Anyone have any thoughts or experience with this type of problem that could help me out?

Is the 1990 350 also a TBI? If it's not, and you have individual injectors, you'll need a high pressure pump to keep fuel to your engine. It will idle fine, but die as you accelerate.

Hi Orfunauto,
Thanks for the reply. Yes the 1990 is TBI also. Over the past couple of weeks it has taken longer and longer to start. Yesterday after I put my driveshaft and trans fluid in and tried to start it, it wouldn't start. So I don't know it this is part of the same problem or not but I fugured I'd mention it in case that would help your diagnosis.

I doubt the problem is your computer. On multiple occasions, I have had to replace my computer because it failed. When the engine finally did start, it would backfire and run very rough when idling. It was impossible to accelerate at all. I think my problem was the failure of the computer to control the timing.

Your problem sounds like a carb or lack of fuel problem to me.

Hello: what is the no# of your ECm 1227747?? or something else?. Make sure fuel pressure is ok, need a min of approx 15 pounds. Adj TPS so it is correct. Do you have a MAP or MAF sensor on your set up. Where is the O2 sensor located, Heated or unheated. Does the engine run ok when in Ign bypass. What kind of dist, HEI external coil or In cap coil HEI. I assume it is a full EST distributor??
Tell me a little more, possibly can help
thanks
Darryl dgilbert78@juno.com

1978elky,
Yes the number you quoted (1227747) is the service number of my computer for the 1990. The number for the 86 is 1227137.

I am using the 1990 computer with the original (1986) wiring. The original wiring has a map sensor that is only hooked up electically, no where to put the vacuum hoses at this point because the 1990 manifold does not incorporate the same vacuum ports and connectors.

The 02 sensor is located on the drivers side exhaust manifold.

It's and HEI ignition with an external coil.

I don't know what an EST distributer is.

The fuel pressure seems to be ok not sure what it is exactly, don't have the equipment to check.

I did have to extend some of the wires so they would reach their destination but I don't think that should be a problem. I did ensure each wire was properly connected and re-checked them.

Thanks a million for your help.

At this time the engine will not run with either computer. It seems to be getting plenty of fuel. I am going to pull the plugs and ensure it is not just flooded (check the simple stuff first).

When you extended the wires, did you solder the connections? If you used any other method in the computer wiring circuits, you will not get accurate data to the computer. All connections, except the soldered type, create a high resistance at the connection which is critical because much of the data is in milivolts and just the smallest resistance is HUGE in such a circuit.

I still do not think you have a computer (ECM) problem.

Hey Spoonplugger,
No I did not solder the connections. The car was at least running before I extended the wires. I am off from work until Monday so I will go back and chech and solder all my connections and see it the car will at least start. If it does then I can start on the other problem of it not running well. I do know that the V-8 cannot run on the original ECM which was designed for the V-6 so I figure I have more than one problem. I appreciate yours and everyone elses input and help. I think this is a great site and I believe with all the assistance from the members we'll get this thing licked.
I'll be back as soon as I get those wires taken care of.

Hey guys,
Part of the problem solved. Put some gas in the TBI and the car started; that narrowed down the problem. Re-connected all my splices with solder, but the car still would not start on it's own. Started looking for electrical issues because I had no juice going to the injectors. Found a blown fuse for the ECM; that did it, it started right up.

Installed the original computer; it runs better but still not the way it should. Doesn't die out when you push the throttle; however I know I have to do more with the computer because it is for the V-6. Can I just replace the prom with one for a V-8? Is that a good place to start?

Thanks again for starting me in the right direction.

Sorry, I do not know the answer to your question about differences in an ECM for a V-6 and V-8. However, I do think the only possible difference is the distributor and timing issues. The M/C solenoid, TPS, O2 Sensor, lock-up torque converter,etc, etc. are not dependent on the number of cylinders and would not be different.

I suggest you go to www.autozone.com and search their site for parts. List one vehicle as a V-6 and search for the part number. Then list the second vehicle as a V-8 and repeat the search. Compare the two numbers to see if they are different. Or, just call them and ask if their system lists two different ECM's.

First the OEM for 86 will not work with TBI . The map sensor hooks to frt. of TBI and set on bracken to the right of TBI view from steering wheel. the 90 model use smaller type dist. DO you see being spray when crank and no started? Check and make sure you have inj. pulse and fuel presse
the fuel pump use a relay to turn on the pump for 2 seconds just a enough to get started and then runs off oil pressur switch. The proper psi for TBI is 9 to 13 psi. Check for spark also Gm exsternal coils have know to bad. :?

I have the correct ECM, MAP sensor, ESC, and fuel relay. Found out the ECM had a bad PROM. fried the fuel relay connections which fried my new PROM. I am looking for a wiring schematic for the 1990 engine so I can see where the differences are. It is somewhere in the fuel relay wiring; I think. Everything else seems to match up well. I was wondering why the fuel relay wiring was connected to the oil pressure switch. The original 86 already had TBI that is why I stayed with it and located a newer setup.
So I have the 1990 set up with the 86 wire harness. I think that's where the problem lies. If I can locate the schematic I can figure that out.

I see no reason why the engine should be a problem. Your fuel pump should run for approx two seconds when the ign switch is turned on, then should stop. If that does not work, start troubleshooting there. The oil pressure switch is also wired into the fuel pump circuit. This supplies a parallel ckt to the fuel pump once about 4 pounds of oil pressure is built up. I think this in case the primary pump circuit fails in the ECM. If you crank the engine enough to get at least 4 pounds of oil pressure the pump should be running. You will need however a prom from a V8 engine. Probably a 87 chev pickup prom I would say that had a 5.7 engine. so hows it going so far
Darryl dgilbert78@juno.com

I have the correct ECM and PROM, however I believe the wiring harnes from the 86 is slightly different from the 90, therefore I need to look at and compare the diagrams before I spend money on another PROM. The fuel pump and relay and oil pressure switch work as designed. I have good fuel pressure but something caused the connection to fry. It may be just a loose connection. I just want to be sure before I spend more unnecessary money that I can't afford at this point. I have spent way more than I budgeted when I started this.

Hello: If you have an 86 harnass I assume you are using the 1227747 ECM. I have an 85 using a 1227747 ECM with the 85 harnass, do not know how close the 86 harnass is to the 85 harnass. The fuel pump is run by the ECM, so you don't want to have bad or wrong connections here, for sure. Exactly which connector did you fry?? The one that plugs on to the fuel relay that is mounted on top of the pass fender well?? At the ECM by the pass kick panel is where the ECM lies. See if there is a harnass number taped to the harnass in that area. Should be about where all the wires bundle together close to the ECM. I will check against my number to see if the same as an 85 harnass
good luck
Darryl... dgilbert78@juno.com

Hi,
You are correct in both of your assumptions. I am using the 122747 with the 86 harness and I fried the connector at the fuel pump relay on the fender well.
I intially assumed since the connectors at the ECM were interchangable that the wiring should be the same. I still think that I may have had a loose connection at the fuel relay which caused my problems. However I don't want to chance blowing another $100 bucks if I don't have to. I have located an after market harness that will work but it is $325. I'd rather spend $25 on a manual and compare the diagrams and harnesses.
Now, if you know of a better way of finding the problem, I am open to suggestions.
Thanks for you reply; looking forward to your suggestions - I am fresh out of ideas at this point.
I am actually focusing on hurrican Rita and making preparations to "get out of Dogde". It is coming entirely too close for comfort. So as soon as I get time I will look at the #'s on the harness at the ECM.

Hello: I have been where you are going, no need to reinvent the wheel. I have everything you will need. If the 86 and 85 harnass are the same I will have the info and you will be in fine shape. I currently have a 350 TBI installed and running in a 1985. Used the 85 harnass with no problem. I did however have to lengthen a few wires because the harnass is for a V6. Some of the wires will no longer be used. I did not use any of the transmission wires (installed a manual trans) I did not use any of the AIR diverter wires, Threw them away. Did not use any EGR, disabled all that crap in the ECM ( can send you a chip if you like for a V8, no problem) Hopefully Rita will not get you, I hate those things. Being in Tampa they get to close for me sometimes. Let me know on the harnass and I can help. I would guess they are about the same. I had a 4.3 V6 with a metric 200 trans. Now have a 1978 355 with a 1987 TBI intake manifold. It works just fine
good luck
Darry........

Well,
We made it through Rita. Headed northwest for about 250 miles and sat tight until Sunday morning. Had no damage at the house, just a few downed branches. So we were blessed this time.
Sounds like you have been through the same thing I am going through now. Only difference is my donor vehicle was a 1990; but if we're running the same computer (1227747) and chip/PROM (16139566) that should not make a difference. I am running the same MAP sensor also; which one are you using? So, yes I do need another PROM.
I have the instructions including all the part numbers for a conversion. If you are interested/curious I can e-mail them to you if you would like. I just need your e-mail address.

I haven't done anything lately as I wanted to be sure I have everything in order before I start replacing parts again. So any information you have I will be forever grateful. My e-mail address is "njpilot@sbcglobal.net" without the quotes.