Larry Dunlap

My son's 1990 firebird, 6cylinder car took a dump yesterday. It started running really rough and showed a check engine light, which turned out to be a code 33. The book shows this as a MAP low vacuum problem I believe. By the time I got home and looked at is it would not start at all. When you try to start it, it seems to start, runs roughly for a few seconds, then dies. If you try to give it gas it dies immediately.

We changed the MAP sensor, I didn't think it would do anything, and it didn't. Im not sure what to try next. A few years ago it did something similar and I changed the ECM, worked perfect.

What should I try, IAC, TPS. Ive checked the vacuum lines and do not see anything obvious.

????

OldCelica

Your code 33 is probably caused by the rough running condition.

Before just throwing money at the issue I would troubleshoot it out. I would start with fuel pressure. Then spark and go from there.

Larry Dunlap

Sounds good. I know how to check the fuel pressure. What is the best way to check for spark?

OldCelica

the easiest way (And the way I start if I think I have a spark issue) is to hook a timing light up to each plug wire and see if the light is triggered. If it doesn't then you are not getting a signal to that wire. You can do this for the coil wire too. This doesn't test the strength of the spark, just the presence.

the BEST way to check for spark is to purchase something like this:
http://www.arizonatools.com/tools/ig...n=productfeeds

A tool like this will allow you to check the strength of your spark too. You just ground the clip and hook your wires one by one and adjust the gap to test the strength.

I don't know how strong your spark should be. I have never actually used a tool like this. I just usually use a spark plug touching it to ground.

Larry Dunlap

Checked all spark wires with the timing light and they seemed okay, Checked fuel pressure and it was also okay. Might this be an issue related to the ECM?

OldCelica

Possible, but I really doubt it in this case. The next thing I would do is hook a vacuum gauge up to manifold vacuum and see if it is in spec. If that is then I would pull all the spark plugs out and inspect them. Look at the color of the insulator on each plug. Your book should have what the plugs may look like and what each one means. Hayne's manuals have a nice color page I think on the back cover.

Also, while you have the plugs out might as well do a compression test on all cylinders as well. Instructions for this should be in your book as well.

Larry Dunlap

The car went from running fine, to running rough, to not starting at all in the same day, matter of hours. Now it seems like it wants to start, runs for about 5 seconds, then dies. If you give it gas it dies immediately. I cant see it being something major like low compression in the cylinders. We tested the TPS and is seemed bad, but I bought a new one and there was no difference. I don't have time to work on it right now so I taking it to the shop today. Will let you know.
thanks

OldCelica

My guess is that you have an injector that is either open or shorted. Let me know what the issue was for sure. I'm curious to see if I'm right.

Larry Dunlap

Good guess. My son is handling the repairs but he told me the shop told him that the wiring harness "broke" and shorte out one or more injectors, also fried the ECM. We are going to see if they can repair the harness and replace any shorted injectors. If it is more than one injector I think we are going to replace all with Accel or Ford injectors. I see where guys think the Ford ones are better but I may not be able to get them as fast as the Accel. I priced a rebuilt ECM the other day at Oreilly Auto parts and it is like $60 plus a $40 core charge. IF they can repair the wiring harness, even if we buy a whole set of injectors it should be like less than $300 in parts plus labor. There is not that much labor in changing injectors and ECM so Im hoping we still have some money for Christmas left

Larry Dunlap

$900 + including towing, repairing the wiring harness, one GM injector (thats all we could find locally fast), rebuilt ecm, plenum gasket plus labor. Geez, ridiculous, I could have done it easy myself except for repairing the wiring harness. Sometimes I hate cars, then again....

draco

Sorry for digging up an old thread, but I'm having an identical issue. Did the shop tell you which section of harness they repaired?

OrangeBird

iTrader: (1)

Hi draco ,

When I was having issues with wiring , it turned out that GM saw fit to run the biggest engine harness right next to the right hand exhaust manifold . When the manifold to head bolt broke and fell out on it's own (seems to be a common failure on our engines) it let hot exhaust gas get blown directly onto the harness and melted it into a short circuited mess ! Yep , fire , being blown onto the wires , how flippin lovely !!! .... Anyway , the fix was , of course , to insulate all the now bare wires , replace the broken bolt , and relocate the harness to be far away from the manifold .

In your situation , we can't be sure it IS wires till you inspect the harness , looking for the kinds of things I found ... The Previous owner of my car $pent considerable $$$ replacing sensors and everything else , except fixing the wiring ! Once I fixed that , it runs like a brand new engine (and it should , with all the new parts )..........

And now , because a picture truly IS worth 10,000 words , here is the section of harness that got fried on my car . I hope your problem is as easy to diagnose !!!!!