Weird hesitation
Thread Starter
7th Gear
Joined: Mar 2007
Posts: 7
Likes: 0
Weird hesitation
Howdy from San Jose, Ca
I just bough a 85' TPI automatic with a 52mm throttle body, headers, full exhuast(true duels)smog pump delete,no cats.
The problem that im having is very weird hesitation.
On a cold start it will idle fine but as soon as you give it allitle gas it will bog down ,pop up the intake and act very lean. If you floor it itll take off like a bat outta hell. But as soon as you get to the 1/4-1/2 throttle position again it bogs back down again,acting as if its gonna die.
When it warms up the hesitation gets less severe but changes sometimes too. Sometimes I can be driving and it runs PERFECT. But sometimes this weird thing happens. Lets say your cruising at 40mph in O/D. If I let off the gas then slowly apply it again it seems that it will not respond for the first second or two then itll kinda slowly respond back to life and cruise normal again. Also it kind of comes in and out of the hesitation as if its electrical,Kind of like itll hit a switch and run perfect again. Again if you floor it there is no hesitation and it takes off like a bat outta hell.
Has code 34,54 in computer
Fuel pressure is in specs throught all driving conditions(even when the hesitation is happening
TPS is set and is smooth the entire range(no drops)
Timing is set
CTS is withing specs throught the entire temp range
MAF has a good reading throught range (disconnecting MAF doesnt help the hesitation)
car does not have any vacuum leaks (I tested this the most)
egr is working properly
O2 sensor is very responsive (and new)
im beginning to think this is a computer problem due to the fact that itll run perfect sometimes then *blink* here is the hesitation again.
Thanks for any thoughts or help
pat
I just bough a 85' TPI automatic with a 52mm throttle body, headers, full exhuast(true duels)smog pump delete,no cats.
The problem that im having is very weird hesitation.
On a cold start it will idle fine but as soon as you give it allitle gas it will bog down ,pop up the intake and act very lean. If you floor it itll take off like a bat outta hell. But as soon as you get to the 1/4-1/2 throttle position again it bogs back down again,acting as if its gonna die.
When it warms up the hesitation gets less severe but changes sometimes too. Sometimes I can be driving and it runs PERFECT. But sometimes this weird thing happens. Lets say your cruising at 40mph in O/D. If I let off the gas then slowly apply it again it seems that it will not respond for the first second or two then itll kinda slowly respond back to life and cruise normal again. Also it kind of comes in and out of the hesitation as if its electrical,Kind of like itll hit a switch and run perfect again. Again if you floor it there is no hesitation and it takes off like a bat outta hell.
Has code 34,54 in computer
Fuel pressure is in specs throught all driving conditions(even when the hesitation is happening
TPS is set and is smooth the entire range(no drops)
Timing is set
CTS is withing specs throught the entire temp range
MAF has a good reading throught range (disconnecting MAF doesnt help the hesitation)
car does not have any vacuum leaks (I tested this the most)
egr is working properly
O2 sensor is very responsive (and new)
im beginning to think this is a computer problem due to the fact that itll run perfect sometimes then *blink* here is the hesitation again.
Thanks for any thoughts or help
pat
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Check the connections at the ECM for cleanliness and make sure they are firm and tight.
Check all the ground connections, make sure they are clean and tight.
Test the relays for the MAF, and check their connections.
Check for any shorts or weak connections on any of the sensor circuits.
Check the Air injection reaction system and make sure its not malfunctioning, and also check around the left hand exhaust manifold to make sure there is no air being sucked into the exhaust stream and being seen by the O2 sensor (could also be blown in from the AIR system).
The fact you say it goes hard everytime at WOT leads me to believe your fuel delivery is good, but ohm test the injectors just for the hell of it.
Check all the ground connections, make sure they are clean and tight.
Test the relays for the MAF, and check their connections.
Check for any shorts or weak connections on any of the sensor circuits.
Check the Air injection reaction system and make sure its not malfunctioning, and also check around the left hand exhaust manifold to make sure there is no air being sucked into the exhaust stream and being seen by the O2 sensor (could also be blown in from the AIR system).
The fact you say it goes hard everytime at WOT leads me to believe your fuel delivery is good, but ohm test the injectors just for the hell of it.
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
I think the CaseMan is on the case here........
Code 54??
Isn't Code 54 a 'voltage monitor' on the fuel pump B+ line ?
That may be a critical piece of data if it is.
Wonder if the pump is losing voltage because of an intermittent connection....
Have you driven around with a fuel pressure gage taped to your windshield?
There are some connections at the top of the tank you may want to check for integrity also.
Code 34?? Doesn't that have something to do with the signals from the MAF??
Check all the connectors associated with that.
Are you SURE the TPS doesn't have a dead spot in it..... can you ohm check it while you're slowly moving the throttle several times to make sure?? I've seen them have 'noisy' spots where the voltage sent to the ECM would fluctuate. It's just a carbon track in there the wiper runs on , just like the old time radio volume controls. You know how scratchy they would get sometimes.
Looks like you've been doing a good job chasing this down.
You'll find it.
Code 54??
Isn't Code 54 a 'voltage monitor' on the fuel pump B+ line ?
That may be a critical piece of data if it is.
Wonder if the pump is losing voltage because of an intermittent connection....
Have you driven around with a fuel pressure gage taped to your windshield?
There are some connections at the top of the tank you may want to check for integrity also.
Code 34?? Doesn't that have something to do with the signals from the MAF??
Check all the connectors associated with that.
Are you SURE the TPS doesn't have a dead spot in it..... can you ohm check it while you're slowly moving the throttle several times to make sure?? I've seen them have 'noisy' spots where the voltage sent to the ECM would fluctuate. It's just a carbon track in there the wiper runs on , just like the old time radio volume controls. You know how scratchy they would get sometimes.
Looks like you've been doing a good job chasing this down.
You'll find it.
Last edited by VetNutJim; Mar 9, 2007 at 12:56 PM.
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Cheers Jimmy, spot on with your codes there mate, i reckon its going to be "bad connection" related with something somewhere, since it comes and goes like it does.
Great to see he gave us a good full bodied report on what he had and hadnt done, makes it so much easier to help!!!
Great to see he gave us a good full bodied report on what he had and hadnt done, makes it so much easier to help!!!
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
Cheers Jimmy, spot on with your codes there mate, i reckon its going to be "bad connection" related with something somewhere, since it comes and goes like it does.
Great to see he gave us a good full bodied report on what he had and hadnt done, makes it so much easier to help!!!
Great to see he gave us a good full bodied report on what he had and hadnt done, makes it so much easier to help!!!
CFI-EFI would be proud!!!!
3rd Gear
Joined: Apr 2007
Posts: 3
Likes: 0
I just went thru the similar situation with my 85 vette. I thought it was all electronic but everything I checked seemed to be OK. I had back fire with hesitation at times. I found the plug wires were the problem. Replaced them and the engine ran like it was made too. It was a cheap fix for me.
