Poor Idle, High Map (long)
 

I've searched through the archives and can't solve this problem. The car was running fine until yesterday. Suddenly my map is 70-80 at idle when it's normally at 45. It's now running way rich blms are around 100 and my sparkplugs are fuel soaked. The only thing wrong that I could see was that the line going from the evap canister to the return fuel line was off. I hooked it back up but it didn't help.

I have a speed density 5.7tpi, 5speed with zz4 cam. Custom prom. I don't think it's prom or ecm, as car was fine before yesterday. I made no changes to car. I may have small header gasket leak, but I would think that would cause a lean condition. The valves look like their working OK. I took off a couple spark plug wires and there was very little change in idle.

I'm leaning toward weak spark. Could the sparkplugs have gotten ruined in 10 minutes of over-rich condition? MAP is working and I couldn't find any vacuum leaks. This is my third engine in 3 years, I hoping that this isn't something internal & expensive.

Just remembered, IAC was at 160 steps at idle, it goes lower while I'm driving. Also no codes are being set.

Replaced plugs, checked wires, rotor, cap, iac, tps. Fuel pressure is at 40-43, same as when it was running good. Any ideas?

High MAP = low vacuum, have you checked for leaks? loose hoses to the plenum and so on...

IAC steps, I have around 10 at idle..........

/N.

Check to see if there is fuel in the vacuum hose to the fuel pressure regulator, sounds like the diaphram is torn & fuel is passing through to the vacuum side. This will cause low map, fouled plugs, & high IAC.

That diaphram idea sounded real good. But I checked this morning and there was no gas smell and nothing leaked out of the regulator. I took into a mechanic and they can't figure it out either.

Any other ideas?

Tough one! I would have to say the ecm is still in control of fuel delivery ie; blm=100 (ecm subtracting fuel), IAC 160 (ecm trying to improve idle) MAP 70-80 (ecm sees that intake vacuum is low) so knowing that I would say ecm is in control of a poorly running engine, IMO. Now you need to find out where all this extra fuel is coming from. We know it is not the fuel pres reg, look at vaccum hoses to evap canister at the throttle body, possibly it is pulling fuel from canister. The other thought lingering in the back of my head is a blown head gasket between cylinders or stuck intake valve or buned valve,seat causing exhaust to revert into intake manifold during operation, this will always cause low intake vacuum (high MAP). If you cannot find a fuel source entering the engine other than the injectors, do a compression check, if that looks good, I'll bang my head against the wall harder.

I know you're not supposed to throw money at a problem, but I'm having the fuel pump changed out. It still had the original pump in it, so I figure it's going to go one of these days. Also the fuel pressure gauge is now reading 18lbs. Either I messed up the Holley AFPR when I opened it up and put it back together (everything looked fine), or the pump maybe bad.

Can a pump if it's going bad, first put out too much pressure then not enough? The engine still sounds pretty smooth once it's going at a higher rpm. Map values come down to the 40's and 50's.

I'm getting ready to park it downtown Cleveland and let it get stolen.

18lbs is not good. To eliminate poss fuel pump, pinch off return hose at rubber line & read pressure gauge. You should see the maximium pressure the pump is capable of. I would expect 60 psi. I was assuming that had been checked by the mechanic. The fuel pump is a major job in a third gen. That is gonna set you back some $$$ if you can't do it yourself. Check fuel pressure as I described, if pump can't make the pressure, then change it. If the pump can make the pressure, recheck the AFPR assembly because something is wrong with it. Low pressure indeed will cause these type of problems, what is your injector base pulse width in milliseconds?

I'll check on the pressure, but I'll still probably get the pump changed. It's the original pump which is 13 years old. It will be $150 labor and I supply the pump. That price didn't sound too bad.

The afpr only had 3 parts inside, diaphram, spring, top button. I can usually screw anything up, but I think I got this right.

You sure I have rubber return lines. I can only recall the metal lines. I'll take a look tomorrow, the car is at the shop.

Thanks,

JJ

If this board ever goes down, I'll have to sell car, not too many shops will even bother with these cars anymore.

The rubber lines are at the left front inner fender by the alternator.

I went Sunday to the shop and changed sparkplugs. I figured they were fouled again again. Well they were mostly fouled except for #5 which looked brand new and #8 that fuel on half the plug while the half was untouched. So the #5 injector isn't firing and the #8 is weak. I'm going to remove the fuel rail and have them cleaned. I know a shop that will do this for $15. Added bonus is that we can see the how the injectors are firing.

I've decided to go ahead and have the fuel pump changed out anyway. It's over 12 years old and specific to the 305 engine. Unless it's a magic pump, it's probably on it's last legs anyway. I got a rate of $150 to replace pump and that sounded cheap. Plus with my new 350, it wouldn't hurt to have a larger volume pump. I bought a Walbro 190. That should give more than enough fuel.

I'll post results later this week. Thanks for everyones help.

Had injectors cleaned, 4 were leaking and the #5 was only working intermittently. Replaced injectors with SVO's. Had the fuel pump changed out anyway. Car is running right again.

Thanks everyone,

JJ

JJ

Having a similar problem and about to buy injectors. I too have a 350, mine's stock. What lb/hr did you purchase? Thanks

I ordered the svo 24lb. They fit perfectly. I just started working on a new prom so I couldn't tell you if the svo's run richer than advertised.