91 Brougham still backfiring

[JerRita]

Hi all I hate to bother y'all again but one our 91 broughams has a 5.7 and runs great UNTIL sometimes it backfires, bucks and smells of gas. It happens with no warning and 2 pro mechanics have not been able to get the car to do it at the shop I can drive it 15-20 minutes at highway speeds and then it does it When it stalls it will not start for another 30-45 minutes So by the time a tow truck comes it starts and drives fine It does not do it all the time so we cannot determine if it is a ignition or fuel issue I checked all the items some of you mentioned earlier The service light came on once and gave the MAP sensor code other than that no codes Could it be a bad computer? I have another 91 w/ 5.0 so the computers won't be compatible right? Thanks again for your help I am afraid to drive it Thanks JeRita 50 miles east of NYC 

[Dave Shepherd]

50 miles e of NYC, I used to live in North Bellmore.  Anyway, you need to find a way to see if you have spark when this happens, also take starting fluid with you and spray some into the intake if it fires you have a fuel delivery issue, only way to pin down which system is at fault here.

[TJ Hopland]

Its a TBI so removing the air cleaner lid / housing you will be able to see the fuel leaving the injectors.    Have a look at it when its running normally so you know what amount of fuel is 'normal'. 

I would guess the map code was likely the result of the back fire, not the cause.  I dont remember MAPs being a common failure item on this design.  This was basically the 87-95 truck motor and EFI system.  I do remember if the base timing and idle was set wrong they would run like total crap but again since this was not an unusual drive train and its not that outdated I would hope your mechanics are familiar with it.  I have bought things with this engine that were not running right and there was usually a MAP sensor and ignition module in the glove box.  All I had to do was set the timing and base idle properly and they settled down.

I cant remember, I think these still had the pickup in the distributor IE not a crank trigger?   I think the module was in the distributor and then the coil was sitting on the intake?

[Roger Zimmermann]

You may have a bad engine ground; the symptoms you are describing are similar to problems I saw here in Switzerland on 4.1 and 4.5 Cad engines. There was a stud near the starter motor which had to be removed, the threads in the block cleaned.
You engine is cast iron but who knows, bad ground can happens also on this type of engine.

[JerRita]

Thanks TJ and Roger No work was done to thew car prior to the problem I have driven trucks with this engine for many years and when the ignition module crapped out they would not start at all Maybe mine is shorting or as Roger said has a bad ground Has anyone else on the forum ever had a similar problem? Thanks JeRita