kevnlou

hi, im a new member, and i am in need of help. i have a 1990 chevy g20 5.7 v8 with tbi, and cannot get it to tick over and run. i have changed, plugs, leads distributor, distributor cap , and rotor, and had the injectors serviced and cleaned.i have spark, and petrol going into the throttle body and injectors, any help would be greatly appreciated . thanks. ive also changed the fuel filter.

oldchevy

You may have fuel, but is it at the correct pressure. Do pressure check on the fuel. You can also spray some starting fluid down the throttle body and see if it runs for few seconds. If it does then you do not have enough pressure and will need to change the fuel pump.

canucklehead

So it cranks fine but will not fire?
If you have fuel going in from the injectors, and you are sure that you have spark, then it must be timing, or mixture. The tip from old chevy will confirm mixture, timing could be off if plug wires or on wrong. I would double check their order.

kevnlou

i double checked all leads and there in the correct order, also i noticed today that it does fire, but dies straight away, and it sounds like its sucking air. im not a mechanic, or even a diy mechanic, im trying to do it all by the manual. so any help is fastanstic, i just need it in lamans terms lol

canucklehead

I had worn spark plugs in my 95 g20, and the plug gaps were too wide. It made it hard to cold start. It would turn over, fire for a second then die and then not fire after that. I took out one plug and closed the gap and bit, and it fired right up. I changed to new plugs that evening.
Now if the plugs are fine, then Oldchevy's advice out fuel pressure might be the next step to check. If you hear the fuel pump running, and the filter is on correctly, and is the right one, then you should have pressure, but is it enough?
Try squirting some raw fuel down the throttle body. It should fire up and rev up to a high rpm then run out of gas and die....if it does that...you have a fuel delivery problem. You can have the pressure tested, but at this point i would have a shop look at it. (changing the fuel pump means dropping the fuel tank....not a diy project.)
Also, pick up a haynes repair manual. They are well worth the 25 bucks for some in depth know how info.
ps. i never asked you if this van ran fine before you changed all the stuff you mentioned in your first post....?

kevnlou

i think ive narrowed it down to the map sensor, as when i remove the pipe that goes into it, the engine will run, and when i replace it the engine cuts out. now my question is this, what is a map sensor for, and can they be repaired, cleaned, or do i just need a new one.

canucklehead

Manifold absolute pressure. It gauges the air pressure in the intake to tell the computer info that changes timing, fuel mixture, and other stuff. You need a new one it sounds like. I don't think they can be fixed. I believe you will have fault codes if its bad. I wonder why your engine light is not on.
After you replace the map sensor, I would get a shop to hook you up to a code reader.

kevnlou

i put a new one on, but still the same, take pipe of to it, engine runs, put it back on engine dies. i have no engine lights on, so i will check all fuses and relays. wiring in van is shocking, has had alot of bodge jobs done.

canucklehead

Clogged Air filter?

kevnlou

its a new air filter, ive just ordered a new iac valve, so ill see if that helps.