Fuel pressure question

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Jun 5, 2005 | 10:10 PM

hyperbaja

Thread Starter

Intermediate

Joined: Dec 2003

Posts: 28

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From: Lewis Center Ohio

Fuel pressure question

1988, 59k miles

gets bad mileage (22 best ever), doesn't like starting when warm, all the signs of bad injectors.

Hooked the fuel pressure gauge to it today.
Idle pressure- 38psi
1000RPM-35psi
engine off-44 psi
5 minutes after engine was shut off-40 psi
10 minutes after engine was shut off-32psi

Starts great when cold, but if you drive it somewhere, get out, come back 15 min later it cranks for a while, then when it starts runs very rich. O2 sensor was replaced 200 miles ago.

Also-Engine will idle at 600rpm, and then surge to 700/800.

What should the temperature be? Normally runs 220 deg.

Jun 5, 2005 | 10:49 PM

bmalec

Racer

Joined: Aug 2004

Posts: 379

Likes: 170

From: Buffalo Grove IL

Fuel pressure looks good. Have you checked the resistance of your injectors yet? I bet you'll find some bad ones--they should be around 15-16 ohms.

Temp sounds a bit high, is that the temp you get while just cruising down the highway? 220 is typical in stop-and-go driving with the stock fan settings-they kick in around 225-228 degrees.

Good luck!

Ben

Jun 6, 2005 | 12:37 AM

hippy

Le Mans Master

Joined: May 2000

Posts: 7,033

Likes: 12

If you have 32 psi 10 minutes after the engine is off I wouldn't look at the injectors as having a leak down problem.

Jun 6, 2005 | 12:52 AM

65Z01

Team Owner

Joined: Dec 2000

Posts: 90,675

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From: SE NY

Cruise-In II Veteran

Use a paper clip to jumper the ALDL pins A & B (upper right) and start the engine while you observe the SES flashes.

After a minute or so the flashes will slow from 2Hz to 1Hz as the ECM goes into closed loop mode. Once the ECM is in closed loop the flashes should have equal On/Off duration, indicating that the ECM is maintaining stoch A/F ratio. If not, the problem is either with the O2 sensor or the coolant temp switch in the front of the intake base under the TB.

A problem with this coolant temp sensor could account for hard warm starting as well as rich running if the ECM is always seeing too cold of a condition.

If idle is surging you might check for a vacuum leak (inlcuding a leaking EGR diaphram) or a dirty TB or IAC (right side of the TB).

Last edited by 65Z01; Jun 6, 2005 at 12:55 AM.

Jun 6, 2005 | 10:42 AM

tjwong

Le Mans Master

Joined: Jan 2003

Posts: 8,596

Likes: 19

From: Portland Oregon

Quote:

Originally Posted by hyperbaja

Do you have access to a scan tool? If you do drive it and see where the fuel trims are hanging. If the trims are near 108 I would be willing to bet that you do have some injector problems. It could even be a MAF issue telling the ECM that there is more air flowing into the engnie than there really is which would cause a rich condition and the O2 sensor is telling the ECM to cut back on fuel. Another problem could be with the engine coolant temp sensor having resistance in the connection. This would cause a lower than actual temperature which in turn would cause more fuel to be added based on what the ECM sees. If the temp sensor was totally open circuit the ECM would see -40 degrees C and would pour fuel into the engine.

When you say its "rich" when it starts after a prolonged cranking, does it actually blow out black smoke? Or does it just smell rich? Have you checked the ignition system? Worn plugs will also cause a prolonged cranking, as will a weak coil. Coils will often act up when then underhood temperatures are high.

Jun 12, 2005 | 09:29 PM