I just rebuilt a 350 for my 90 chevy pickup.  The engine was bored .030 and at the suggestion of my machine shop I put a different cam and lifters in it to increase gas mileage.  Timming has changed from TBC to 5 before TDC.  I ran it through the break in for the cam (2000 rmp for 20 min).  But then I started to get codes.  It has coded 32, 33, 45 and the last one was 15.  I have changed the egr, tried a different MAP (but got the same result so I went back to the orginal) and I changed the O2 sensor.  The O2 was the last thing I changed and it was very black from carbon.  I can see gas pouring in from the injectors (very wet spray pattern).

I was thinking the cam may be causing the problem but I'm not sure what to do to fix it.  When I checked the vac at the manifold it was just about 17 with a small rapid fluctuation.

Any suggestions??
Dan  

first disconnect neg bat cable for 1 minuet to clear codes and drive your truck at hwy speeds for several miles and see if it sets another code. you may have just loaded it up and set false codes. if have any other questions just ask.

thanks
Lee  

If the cam you installed is different enough from stock, you might need to get an aftermarket chip for the computer. I've got a '92 Silverado, had to do the same thing.

That being said, follow the advice above first, but also include a plug change. Also make sure your TPS hasn't gone bad, and the fuel pressure regulator in the TBI unit.  

Lee, I cleared the codes and and took it for a spin (about 24 miles @ 70mph).  It ran rough when I started it, but ran good a hwy speed.  When I stopped to turn around it wanted to die, so I made it quick and got back home.  When I pulled into the yard it died.  I cranked it and it ran very rough, I looked in the TBI and I could see alot of gas running (very wet spray).  While it was running it set a 33 code.  I had just checked the TPS and the MAP before I left and both checked out good electricly.  (they showed what the book said they should as far a voltages)  I also checked the harness voltage coming to those two items and it was correct (per the book).

55 Guy, is there any easy way to check the fuel pressure regulator (short of buying the tool to do so)?  

hey guy, sorry it took so long to get back check your temp sensor for the ecm {It's located at the thermostat housing} it my be reading -34 degrees which will set it in full rich mode.

Thanks
Lee  

Thanks Lee, I'm going to changed it and see what happens.  

Well, still no luck.  I changed the temp sensor and spark plugs (because they were fouled).  It cranks up and misses badddd.  I can just keep it running, sounds like it hits about 5 cylinders and then misses the next 3 and does it all again.  No way to set the timming with it missing so bad.  Still looks like its running rich and it set a 33 code again.  

Code 33 is the MAP sensor, code 15 is coolant sensor, code 32 is EGR, and code 45 is rich exhaust,(What a shock!) Sounds like your manifold absolute pressure sensor crapped out. By the way, what are the specs. on the cam? I think it was 55Guy who said how great this TBI was. Would have never had this problem with a carb!  

Did you test vaccum on the hose to the MAP. sensor? Also check your connection at the ECM.  

Hi there,

Same problem here --- I have a 91 motorhome with a TBI 454 with 80K on it. Starts great and idles and runs perfectly for 5 minutes, then the injectors start dumping fuel into the engine and it starts running rich - real rich, and pretty poorly. Have replaced the fuel pressure regulator diaphram, cleaned injectors, replaced ECM, spark plugs, and checked fuel lines / sending unit for irregularity.

I thought that it may be a thermostat problem that is failing when it comes to temperature? Perhaps an oxygen sensor?

Why is it starting fine and idling fine for several minutes - then racing like a bat outta hell?

Thanks,

Adam.  

Connection is good at the ecm, I checked to vac. on the other side of the TBI.  I'll have to go back and check the hose to the map and the vac at that port on the TBI.  I had a working MAP and changed it a while back (several sensors ago) but nothing changed, so I switched back to the orginal.

Adamstarr - try to unplug the temp sensor when the engine starts to flood and see if it corrects the problem.  The sensor may be stuck.

The cam is a mild perfornace Speed Pro FMP CS1014R Hydraulic Camshaft 420/443
> Int. Duration .050" :204
> Exh Duration  .050" :214
> Int lift 420
> exh lift 443
> Lobe separation 112


Dan  

Ok try this on for size, I tested the map voltage and all is good.  I checked the vac from the TBI at the MAP and it was high at idle (low 20's) and dropped down to about 5 while I was revving the engine to keep it running.  So i capped the vac source from the TBI and put my vac hand pump on the MAP, I put about 17 lbs. vac on it and it ran alot smoother, pumped it to 22 and it still ran better (not great).  I dropped to vac and it flooded and died very quickly.  To me that seems like the MAP is good.  What do you think?  

While I've been working on this I found the ECM chip code is
Serv. no  16144288
>> 86 ATUR
>> K 302690996
>>
>> It has two chips under the cover, one in a plastic carrier, its info is;
>>
>> Silver tag - ATUR
>> .7179
>>
>> On the under side of the chip it has this;
>> JT8(G)/J61P
>> LFI0D249
>> AD09
I've been told this in for a 6cyl, not a 350 v8.  I wonder if that is causing the problems.  The engine ran good when I first completed the rebuild, so I don't know how the chip could be causing all the problems now.

Still Walking
Dan  

That cam should work fine in your set-up without any fuel calibration change. When you said it worked fine in the beginning, did that mean before the rebuild? If so, what is different now besides the cam? Possibly a vaccum line hooked up ported instead of manifold, or vice versa? I do know that the map sensor converts vaccum information, to a voltage output and sends it to the ECM. Such info. is used to control fuel delivery and ign. timing. Have you tried a timing gun to see if anything is not right with the timing? You had said that the timing was changed from 0 to 5 BTDC. What was the reason for the change? you already dealt with the TPS and the coolant sensor, map sensor checks out. Only three other things that I can think of are, restriction in the fuel return line (would cause high fuel pressure), a injector(s) not seating, or welding on the truck without disconnecting the battery. Welding will play hell on ECM and other curcuitry. Does it run fuel out the injectors when key is on, but not started? I run carbs. so I dont get much involved with this computer crap. I have one of those junkers on a spare 454. I will take a look at it and see if I can come up with anything else.  

JW, the engine ran good when I 1st started after the rebuild.  When I got the truck it had a blown head gasket and a bent rod.  The new cam changed the timming to 5 BTDC ( that is where the alignment marks meet).  I timmed it with a gun at 1st but now it won't run smooth enough to time.  OH how I wish this was a carb!

Dan  

If the computer's telling you the MAP is bad, try swapping in a new MAP sensor (they're not expensive) and seeing what happens. Just because it's reading correct voltage doesn't mean there's nothing wrong. Also, check the vacuum line going from the TBI to the MAP sensor for any problems.

Yeah, I said TBI units are great JW454, and I still say that. (smart a**) As with anything that's almost 20 years old (carb equipped or FI equipped) things are going to wear out and need replacing. Look across this board and you'll see plenty of posts with guys having carb troubles and can't figure out what's wrong.